lcd and tv repair guide

8/20/2019 Lcd and Tv Repair Guide

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Troubleshooting and

Repairing LCD TVs

By John Preher

www.preher-tech.com

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http://www.preher-tech.com/http://www.preher-tech.com/


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Copyright

No part of this publication may be reproduced, stored in a retrieval system or transmittedin any form or by any means, electronic, mechanical, photocopying, recording, scanning or

otherwise, except as permitted under Sections 107 or 108 of the 197 !nited States "opyright#ct, without the prior written permission of the publisher or author$

Limit of Liability/Disclaimer of Warranty

%he publisher and the author ma&e no representationsor warranties with respect to the accuracy or completeness of the contents of this wor& and specifically disclaim all warranties, including without limitation warrantiesof fitness for a particular purpose$ No warranty may be created or extended by sales or

promotional materials$ %he advice and strategies contained herein may not be suitable for every situation$ %his wor& is sold with the understanding that the publisher is not engagedin rendering legal, accounting, or other professional services$ 'f professional assistance isre(uired, the services of a competent professional person should be sought$ Neither the publisher nor the author shall be liable for damages arising here from$ %he fact that anorgani)ation or *ebsite is referred to in this wor& as a citation and+or a potential source of further information does not mean that the author or the publisher endorses the informationthe organi)ation or *ebsite may provide or recommendations it may ma&e$ urther,readers should be aware that 'nternet *ebsites listed in this wor& may have changed or disappeared between when this wor& was written and when it is read$

or general in!ormation on our other products and ser"ices or to obtain technical support#

please email our "ustomer "are -epartment contactus.preher/tech$com

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mailto:[email protected]:[email protected]


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Dedication

This book is dedicated to my wife Lindsay , my daughter Alana and my son Kobin. With outthe support of my wonderful family this book would have never been possible.

would also like to dedicate this book to !estine "ong, Author and electronics technician.Thank you for all your support and inspiration.

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Contents

Li$uid %rystals....&Li$uid %rystal 'isplays....()

The *ower +upply oard....(-The nverter oard....22The ain oard....2&The %ontroller/T0%on oard....#1The L%' 'river oard....#-The +tandby %ircuit....#&The Li$uid %rystal 'isplay n 'epth....#Tools....1(

Test 3$uipment....-)+chematic 'iagrams....-45nderstanding and Testing 6esistors....-75nderstanding and Testing %apacitors....5nderstanding and Testing nductors....#5nderstanding and Testing Transistors....5nderstanding and Testing 'iodes....7)5nderstanding and Testing ridge 6ectifiers....()#5nderstanding and Testing L3's....(()5nderstanding and Testing +witching Transformers....((#5nderstanding and Testing 8pto0solators....((5nderstanding and Testing 9oltage 6egulators....(2#5nderstanding and Testing +witches....(2&5nderstanding and Testing :uses....(24+ome Testing Tips....(#(5seful :ormulas....(#2;ow To 'isassemble An L%' T9....(##

9oltage Test *oints....(#&The Tap Test....(11:ree


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nverter oard :ailures....(-4ain oard :ailures....(?o 9ideo....(&7?o Audio....((8+'/enu :ailure....(2White +creen....(#6ainbow +creen....(-+creen :lashes Then T9 +huts 'own....(&?o ack light....(Lines n *icture....(4%racked *anel....(7L%' T9 6epair %ase ;istories....(4)+afety....(4&

%onclusion....(7):urther 6eading....(7(Websites....(71*arts 'istributors....(7-

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Liquid Crystals

Li$uid crystals are a type of matter that posses properties between those ofstandard li$uid and those that are more like solid crystal. Li$uid crystalmay flow like a li$uid but at the molecular level it is oriented in a way thatnormally represents a solid crystal.

Li$uid crystals molecules are rod like and can be aligned when electricityis applied to them.

Liquid Crystals

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3ach sub0pi@el or cell of an L%' panel is made up of li$uid crystalmolecules suspended between two transparent electrodes and twopolari


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efore an electrical current is applied the molecules are in a rela@edBstate. When voltage is applied the molecules align themselves with theelectrodes. The electrodes are treated in a manner that causes the crystalsto align in a helical structure. This type is called Twisted ?ematic =T?> andis one of the most common types in L%' T9s.

Twisted nematic =T?>

Twisted nematic displays contain li$uid crystal elements which twist anduntwist at varying degrees allowing light to pass through. When novoltage is applied to a T? li$uid crystal cell, the light is polari


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Light passing through an L%' panels first polari


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Liquid Crystal Displays

A li$uid crystal display contains a light source/back lighting, a li$uidcrystal panel and circuits that drive the panel.

LCD Display

(ack lihtin The light source is found at the very rear of the display and it contains agroup of thin %%:Ls or %old %athode :luorescent Lamps.

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(ack liht found in LCD T)

CC'Ls used in LCD T) back lihtin

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)arious CC'Ls

The light from the back light passes through diffusers to make sure thatthe light distribution across the display is uniform. ?ote that some newerT9s use L3' back or side lighting and do not have a large bulky back lightand do not re$uire an inverter board. ?e@t the light passes through theL%' panel which is made up of millions of cells. As stated earlier the cells

will control the flow of light through the display to create full colorimages.

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The LCD Panel

The L%' *anel %ontains ultiple Layers. :irst a polari


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As we Dust said the L%' panel contains millions of cells = depending on thescreen si and three cells make up a pi@el. 3ach cell is colored either redgreen or blue. A complete pi@el is made up of one green, one red and oneblue cell. 3ach cell is controlled by a T:T or Thin :ilm Transistor thatprovides accurate control of each cell and makes for a clear picture.

Close look at pi*els and cells !sub-pi*els$

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The "ower #upply (oard

Typical LCD TV P$% &Power $upply %nit'

"- %2s !se a switching type power supply also &nown as an S34S or Switch3ode 4ower Supply$ %he power supply converts the mains #" supply into -"5-irect "urrent6 voltages that can be used by the circuits within the "- %2$

#" 5#lternating "urrent6 at the mains voltage 5usually 110/102 in !S#6 entersthe 4S! and first passes through 3' 5lectromagnetic 'nterference6 filtering, inrush current limiting and 4" 54ower actor "orrection6 circuits$ %hen the #"voltage is rectified by the bridge rectifier$ Note if #ctive 4" is used, the active4" circuit will be located after the bridge rectifier and before the reservoircapacitor$

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Passi"e PC Described

%he simplest way to control harmonic current is to use a filter, filters are designedthat pass current only at line fre(uency 50) or 0 )6$ %his filter reduces theharmonic current, which means that the non/linear device now loo&s li&e a linear

load$ #t this point the power factor can be brought to near unity516, usingcapacitors or inductors as re(uired$ %his filter re(uires large value high currentinductors, which are bul&y and expensive$ 4assive 4" needs an inductor largerthan the inductor in an active 4", but costs less$

(cti"e PC Described

#ctive power factor correction 5active 4"6 uses a more complex electronic

circuit to control the amount of power drawn by a load in order to obtain a powerfactor as close as possible to unity516$ !sually the active 4" circuit controls theinput current of the load so that the current waveform is proportional to the mainsvoltage waveform 5a sine wave6$ %he purpose of ma&ing the power factor as closeto unity516 as possible is to ma&e the circuit that is power factor corrected appear

purely resistive$ 'n this case the voltage and current are in phase and the reactive power consumption is )ero$ %his allows the most efficient delivery of electrical power from the power company to the consumer$ Some types of active 4" are:oost,:uc& and :uc&/boost$ #ctive power factor correction circuits can be single

stage or multistage$ 'n the case of a S34S, a boost converter is inserted betweenthe bridge rectifier and the main input capacitors$ %he boost converter attempts tomaintain a constant -" bus voltage on its output while drawing a current that isconstantly in phase with and at the same fre(uency as the line voltage$

%he #" voltage 's now ;ectified , output from the :ridge rectifier is a pulsed -"voltage which is then s tal& about the power 3?S%+s$ 'n "- %2s you will commonly findtwo power 3?S%s in the typical half bridge topology$

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Basic )al! Bridge Topology

%he 3?S% is a switch in the S34S, it is turned on by the power '" that sends as(uare wave pulsed voltage to the gates of the power 3?S%s in the half bridge,turning them on and off alternately at a high fre(uency$ *hen the first of the

power 3?S%s5@16 is turned on it allows the smoothed -" voltage to flowthrough the primary winding of the switching transformer to the center of thevoltage divider formed by "1 and " $ *hen this 3?S% switches off thesecond 3?S%5@6 is switched on and the flow of current reverses, going fromthe center of the voltage divider to ground through the second 3?S% and then

the process repeats$ %his action induces a voltage in the secondary windings of theswitching transformer, which steps down the voltage in this case, to #" voltageswhich are then again rectified by either ultra fast recovery or schott&y diodes, thenfiltered by secondary side filter capacitors and inductors also called cho&es

because they inhibit or


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:ottom o! P$% showing $*D power +C,hal! bridge dri"er

P$% with acti"e PC18


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%he output of the 4S! is &ept stable by utili)ing feedbac&$ #t least one of thesecondary voltages must be monitored, this is done by a few circuits$ irst thesampling circuit which is normally made up of a few resistors$ %he voltage fromthe sampling circuit is then ta&en to an adAustable shunt regulator '", this is the

error detection circuit which monitors the sampled voltage ta&en from thesampling circuit and then drives an opto/isolator which has an output signal that isamplified and then ta&en to the power '"s feedbac& pin so that the power '" canthen alter the mar& to space ratio of the s(uare wave signal to the 3?S%+scausing a regulation of the output voltage increasing or decreasing the output oreven shutting down the %2 depending on the signal received from the opto/isolator$ %his process is called 4ulse *idth 3odulation or 4*3$ %he power '" issometimes referred to as the 4*354ulse *idth 3odulator6$ 'f the load on the

power supply causes the secondary voltages to drop then the power '" increases

the 3?S%+s drive signals duty cycle or you could say the ratio of mar&s tospaces increases$

*ar to space ratio

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P*

Some 4S!s will use a different type of feed bac& implementing a secondarywinding on the primary side that is used for feedbac&, still the over all principle isthe same and the process is still 4*3$

Basic $*P$ Bloc Diagram

%o go completely 'n depth into the wor&ings of the S34S is beyond the scope ofthis boo&, but you should now have a good idea of how an S34S in an "- %2wor&s$

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' do suggest you read more on S34S and how to repair them because it willdefinitely speed up your troubleshooting time$ *e will go over the S34S muchmore in this boo& but ' would still li&e to recommend you read


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The +n"erter Board

%he inverter board is responsible for stepping up the low -" voltage supplied byone of the outputs from the S34S into a high voltage, roughly 1002/18002 #"for stri&ing5start up6 and 002/10002 #" to run the "" lamps that provide the

bac& lighting for the "- panel$

or many years designers have used a buc&+royer inverter topology to stri&e and

supply power to the ""s$ %his topology is basically a combination of a stepdown buc& regulator, a royer oscillator and a step up transformer$


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Buc Royer circuit simpli!ied

%he buc& regulator is made up of a power transistor, buc& cho&e, buc& diode, buc&coil, power inductor, a 4*3 or inverter '" and a capacitor$

$impli!ied Buc Con"erter

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%he royer oscillator consists of two transistors, capacitor, 2% 5igh 2oltage%ransformer6 and a capacitor in series with the lamp called the ballast capacitor$%he buc& royer inverter supplies a high voltage #" to drive the "" lamps$

' don>t thin& you will come across to many "- %2s with the :uc&+;oyer style

inverter circuit but it is still good to understand how different circuits wor& as youwill see similar circuits employed in different parts of the %2 and other electronicsdevices you decide to repair$ %he maAority of inverter circuits you will encounterin "- %2s will implement 4*3 type inverters such as the direct drive topology$

Direct dri"e topology

%he direct drive inverter uses a simple topology that optimi)es performance, has areduced cost and lowers component count by eliminating the buc& cho&e, buc&diode, resonant capacitors and transistors found in a :uc&+;oyer oscillator$ %hedirect drive topology uses a 4ower '" to drive a pair of 3?S%s connected to a2% primary winding, switching the 3?S%S on and off at separate times,allowing current to flow through the primary windings center tap and bac& andforth through the primary winding and one of the 3?S%s to hot ground$ %hetype of direct drive inverter we Aust discussed may also be referred to as a push

pull circuit$

#nother common type of inverter you will see is the full bridge inverter$

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ull bridge topology

%he full bridge inverter is li&e the direct drive inverter ' showed you earlier onlythe center tapped primary is no longer re(uired$ %he 3?S%s are in a classical/:ridge topology that is used to reverse the current flow through the primarywinding of the high voltage transformer$ Cou will commonly find this type ofinverter in today>s "- %2s$ Note that some %2s you will encounter will have the4S! and the inverter integrated into one board$ Cou may also encounter some

other inverter topologies li&e the half bridge inverter$


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The *ain Board

#s the Name implies the main board has many functions within the "- %2$Cou may also hear this board referred to as the #+- board, logic board, digital

board and also the scaler board$ %he purpose of the main board is to ta&e the inputvideo and audio signals convert the analogue video signal into a digital signal thatthe controller board can use to drive the %%s in the panel and control the picture$%he audio is ta&en to the audio processor than an audio amplifier which thendrives the spea&ers$ Sometimes all of the video and audio inputs will be found onthe main board and sometimes they will be found on a separate board called the

Aac& pac&, which connects to the main board via a ribbon cable or " 5latlexible "able6$ %his board may also house the audio processor and audioamplifier '"s and corresponding circuits$


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LCD TV /ac pac,+nput or signal board

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Next we will discuss important components found on the main board$

VP%&Video Processing %nit'

%he video processing unit is a highly integrated circuit that includes a"4!5"entral 4rocessing !nit6, -5igh -ef$6+S-5Standard -ef$6 video and audiodecoder, N%S" video decoder,?S-5?n Screen -isplay6comb filter a video scalerand de/interlacer$ %o fully explain the 24! is beyond the scope of this boo& and 'suggest you do further studying if you want o understand the 24! better$ %hemain thing for you to understand is it converts video information into digitalsignals that can be sent by the 2-S '" to the controller+%/"on board$

VP% on LCD TV main board

*C%&*icro Controller %nit'

# micro controller is a small computer made up in a single integrated circuitconsisting of a fairly simple "4!5"entral 4rocessing !nit6 along with supportfunctions li&e crystal oscillator, timers, watchdog timer, serial and analog '+? etc$4rogram memory li&e N?; flash or ?%4 ;?3 can be included on chip as well assmall amounts of ;#3$ %he 3"! carries out small dedicated tas&s within the"- %2$

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*C% on LCD TV main board

00PR1*&0lectronically 0rasable Programmable Read 1nly *emory'

4;?3s are a type of non/volatile memory used in electronic devices$ Bust asthe name implies an 4;?3 can be erased and programmed with electricalsignals$ 4;?3s are used to store information such as user adAustable settingsand preferences among other things$ *hen you ma&e for instance a brightnessadAustment the 3"! may store this information in an external 4;?3$

00PR1*$ on LCD TV main board

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Voltage Regulator +Cs

2oltage regulator '"s provide a constant stable voltage for the '"s and othercircuits found on the main board$

lash *emory

lash memory is non/volatile and it is a specific type of 4;?3 that is erasedand programmed in large bloc&s$ lash memory costs much less than byte/

programmable memory 4;?3 and so is dominant wherever a large amount ofnon/volatile memory is needed$ %he "- %2 software is usually stored on flashmemory and this software can sometimes be upgraded through a !S: port ormemory card reader on your %2$

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(udio Processor

%he audio processor receives digital and analogue audio signals input to the %2and converts them into a signal that can be used by the audio amplifier to drive thespea&ers and also to decode and send audio to peripheral devices$

(udio (mpli!ier

%he audio amplifier as the name implies is responsible for receiving the signalfrom the output of the audio processor which is small in amplitude and using it todrive a signal with larger amplitude but the same modulations through the %2spea&ers$

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LVD$&Low Voltage Di!!erential $ignaling'+C

%he 2-S '" uses low voltage differential signaling to send the video signal from

the main board to the %/"on+"- controller board $ 2-S is a differentialsignaling system, meaning that it transmits two different voltages that arecompared at the receiving end$ 2-S uses this difference in voltage to encode thevideo signal$

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Crystals

%he function of the crystal is in combination with other components to create anelectrical signal with a very precise fre(uency$ %his fre(uency is used to provide astable cloc& signal for an '"$ %he most common type you will see in the "- %2

is the (uart) crystal oscillator$

#gain remember that not all "- %2S are the same$ 'n this boo& ' am giving youexamples of what is commonly seen in "- %2s on the mar&et today$ Cou willfind that some %2s will incorporate different technologies on their main boards$ 'tis up to you to do further studying as needed li&e reading the service manual andgoing over the schematics for the %2 you are wor&ing on if possible, but always

be learning about electronics and electronics circuits so can (uic&ly identify themwhen you see them and troubleshoot them (uic&ly as you &now how they operate$

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The LCD Controller Board

%he "- "ontroller or %/"on 4": receives the 2-S signal from the 3ain:oard which it processes into %% -rive Signals and then through the

driver board controls the "- 4anel driver '"s$?n the %/con 4": you will find-ynamic ;am '"Fs which are igh Speed Storage -evices used to store data untilit is time to be addressed$12 is usually supplied to the %/con :oard through thecable from the main board to the %/con board$ %his voltage is easily measured atthe picofuse on the %/con board$

LCD controller board

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The LCD Dri"er Board

%he "- driver board is directly bonded to the "- panel by flexible printedcircuit board54":6$ %he driver board directs the signal from the "- controller

to the driver '"s which are mounted directly to the 4": that bonds the driver board to the "- panel and on 4": down the side of the panel$ Sometimes youwill see different configurations li&e the %/"on+"- controller board and driver

board can be integrated into one board$

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The $tandby Circuit

%he standby circuit is used to supply power to the 3"! and other components in

the "- %2 when the %2 is off, this is why it is called standby mode$ ;eally the%2 is not off completely unless it is unplugged$ %his is how you are able to turnthe %2 on when the %2 is in standby mode$ *hen you push the power button onthe remote control or on the &eyboard located on the %2 a signal is sent to the3"! that tells the 3"! to send a start up signal to the power '" to start drivingthe power 3?S%s which causes the %2 to turn on$ %he standby circuit is foundon the S34S board and is easily located by it>s small switching transformer$ %heusual standby voltage is 2 -"$ %he standby power supply is an S34S usuallywith the 4*3 and 3?S% integrated into a single standby power '", small

switching transformer, secondary diode, filter capacitors, feedbac& circuit etc$ 't isa fully functional S34S only really small, an S34S within and S34S$

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The Li2uid Crystal Display +n Depth

#s we stated before the i(uid "rystal -isplay contains many layers$ # bac& light, polari)ing filters, color filters, %% layer and li(uid crystal$ %he very bac& of the

panel is a bac& light which contains multiple "" lamps$ Some newer %2s use-s for bac& lighting or edge lighting with a light guide, allowing light to evenlyilluminate the entire picture even though the light source is around the edge andnot directly behind$ %he light passes through the actual "- panel that contains allthe tiny red, green and blue cells that ma&e up the pixels allowing the picture thedisplay produces to be illuminated and seen$

Panel Types

Passi"e *atri3/4assive matrix panels use a simple grid to address a particular pixel in the display$#s the number of pixels and the corresponding columns and rows of the gridincrease this type of display becomes infeasible$ Slow response times and badcontrast are typical with this type of display$

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(cti"e *atri3-

3odern "- %2s use the active matrix structure$ %he matrix is made up with %%5%hin ilm %ransistors6$ ach cell within a pixel has its own dedicated transistor$%his allows each cell to be activated individually$

#ctive matrix addressed displays are brighter, sharper and generally have betterresponse times not to mention producing better images than passive matrixaddressed displays of the same si)e$

Response Time

;esponse time is the amount of time it ta&es for a li(uid crystal cell to changefrom activated or white to inactive or blac& and then return to white$ :asically itrefers to the speed of the li(uid crystal cells and how fast they can change fromone state to another and so how fast the images can be refreshed on the screen$ %hefaster the response time the better$ %his reduces the effect of trailing or ghostingthat can be caused by slow response times$ %ypical response times are from Ems/1ms$

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Contrast Ratio

"ontrast ratio is the ratio o the %2s brightest white it can display in comparison to

it>s dar&est blac&$

Viewing (ngle

the viewing angle of the %2 is literally the angle at which it is best viewed from$!sually the hori)ontal and vertical viewing angles will be listed in the usersmanual$ 'deally a %2 would have a viewing angle of 180 degrees both hori)ontallyand vertically, which would mean it could be viewed even if you were standing atthe very side or loo&ing at it from the very top or bottom$ 3odern "- %2s havea wide viewing angle, usually around 170 degrees hori)ontally , vertical viewing

angle can vary$ *hen a %2 has a small viewing angle you will notice the picturefade and the colors distort as you move up and down or side to side relative to the%2$

Resolution

%he resolution of an "- %2 is the number of distinct pixels it can display$ 't issimply the physical number of columns and rows of pixels creating the display$"- %2s commonly display the following resolutions$

S-%25Standard -efinition %26G E80i-%25nhanced -efinition %26G E80p570 x E806-%25igh -efinition %26G 70p5180 x 706-%2G 1080i 5190 x 10806-%2G 1080p 5190 x 10806

%he i stands for interlaced scan$ %his means for each frame you have two


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%he p stands for progressive scan$ %his is when the scan starts at the top of the panel and drives every necessary cell all the way down the screen completing anentire frame in one sweep as appose to two$

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Tools

et>s discuss some tools that are necessary for repairing "- %2s and some thatwill ma&e repairing "- %2s much easier and reduce your troubleshooting time$

Long 4ose Pliers

ong nose pliers come are great for all sorts of things including helping to removeE1


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and place+mount components in places that our fingers can>t fit$

Diagonal Cutters

-iagonal cutters really come in handy$ Hood for cutting of a strip of solder wic&and always being used to clip off components leads after soldering them in place$

4ut Dri"er

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$crew Dri"ers

Twee5ers

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%wee)ers come in handy, especially when you are removing or replacing S3-components$

$oldering 6it

Cou will want to put together a soldering &it that includes such things as solder,solder wic&, solder tip tinner+cleaner, heat sin& compound, a solder suc&er somedental pic&s and a 7solder aid &it=$

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1ptical Visor ith Light

#n optical visor is something ' Aust could not do without, ' use them to find badsolder connections on 4":s and ' basically wear them the whole time ' amwor&ing, when soldering and to loo& at part values for instance on S3-components, it would be very difficult to wor& with out these and it is importantthat they have a light so you can &eep your hands free for things li&e a solderingiron and solder etc$ *ithout proper lighting and magnification it would not be

possible to even see a lot of the connection problems ' have found while ' waswearing them$

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03ample o! solder cracs that you might not see without a light and magni!ier

Variable temperature soldering station with L0D display

# good variable temperature soldering station is an essential if you plan on doingcomponent level repairs on "- %2s$ ' recommend spending the money to get anice station with variable temperature li&e the one in the above photo$ 't willsurely pay for itself in Aust a few repairs$

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$older Tip Cleaner

$*D rewor station

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#n S3- rewor& station is not a must for doing "- %2 repair, but if you decideto ta&e on lot>s of S3- level repair within the "- %2 this will surely ma&e yourlife much easier$

Chip 8uic $*D remo"al it

"hip @uic& is one of my favorite products$ %his is what ' choose to use over anS3- rewor& station for the amount of S3- wor& ' find myself doing$ ' have evenremoved and replaced tsop 5thin small/outline pac&age6 flash '"s with 0 pinswith this stuff and other products form their website, it is ama)ing$

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Complete 0lectronics Tool 6it

#ll the tools listed are Aust some of the most important tools needed, but ' personally feel the more tools the better and ' am &nown for carrying a largeamount with me most of the time$ Cou may want to thin& about purchasing one of

the complete electronics tool &its li&e in the photo above$ Cou can purchase these&its from various electronics distributors online$

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Test 02uipment

D**&Digital *ultimeter'-

-33s in general have less effect on the circuit being tested than an analoguemeter and few circuits are effected by having this type of meter connected to them$3ost -33s have a constant input resistance of 103 ohms or more$

Digital *ultimeter

%he -33 is probably the piece of test e(uipment you will find yourself usingmost as it has so many features$ 3any -33s include settings for resistance, -"and #" voltage, fre(uency and duty cycle, -" and #" current, capacitance,continuity, transistor h, temperature, diode testing and more$ 4urchasing a

(uality -33 is definitely a wise investment$

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(nalogue *eter-

%he analogue meter is also a very useful tool for the electronics technician$ %hevoltages used by the meter for testing are larger than with a -33 and so they can


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The 0$R *eter-

%he S; meter is an important tool for the electronics technician or hobbyist$lectrolytic capacitors that have increases in S; are often the reason electronicdevices fail$ :ad electrolytic filter capacitors in the S34S can cause all sorts of

problems in "- %2s including no or dim display, flic&ering display, no powernor audio etc$ %here is also lot>s of electrolytic capacitors on the main board whichcan also cause many problems li&e loss of ?S-, artifacts+glitches in the picture no

video etc$ when the capacitors fail$S; stands for (uivalent Series ;esistance and is and effective resistance that isused to describe the resistive aspect of the impedance of certain electricalcomponents$ %he theoretical treatment of capacitors assumes they are perfectcomponents contributing only capacitance to a circuit, but all physical devices areconstructed of material with some resistance to electricity$ %his means a capacitorhas a resistance as well as a capacitance$ "apacitors also exhibit reactance whichwe will not discuss now$3ost electrolytic capacitors have a low S; to begin with, depending on a

specific capacitor and the average S; can usually be found on the spec$ sheet fora certain capacitor if you can find one$ 3ost li&ely you will refer to the chart ofcommon S; values that will come with your S; meter or you can also findthem listed on the internet$ Normally with a bad electrolytic capacitor the S; is(uite higher than the common range$ # capacitor S; rises over time as they areexposed to and or dissipate heat, because they contain a li(uid electrolyte when


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they get hot the li(uid expands and is vented out of the capacitor and also theelectrolyte can brea& down and go through chemical changes over time andexposure to heat also causing the S; to increase$%he S; meter is so valuable because it allows you to (uic&ly chec& the manyelectrolytic capacitors found in "- %2s and other electronic devices and very

often you can test them in circuit all though if you ever doubt the reading it neverhurts to test the capacitors out of circuit and this is a good practice with allcomponents or at least to unsolder and lift one of the components leads from thecircuit$

The Ring Tester-

%he ring tester is an inexpensive and effective way to test any high @ inductivecomponent$ 'n "- %2 repair the ring tester is very useful for testing switching

transformers in the S34S and 2 transformers on the inverter board$%he components in many circuit li&e the S34S and inverter board contain lowloss5high @6 resonant circuits$ %he ring test got its name from the fact that when avery fast pulse of current is sent through a high @ circuit the tuned nature of thecircuit will produce a decaying #" voltage of several cycles or more$ %he morerings the higher the @$ ittle or no rings indicates low @ and a problem$

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The 1scilloscope-

%he oscilloscope or


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Digital Capacitance *eter-

# digital capacitance meter with a large range is a good tool for testing capacitorscapacitance value$


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Lea $eeer-

%his is a great tool for hunting down difficult to find shorted componentsespecially circuits with lot>s of S3- components$ Simply touch ea&See&er>sgold/plated probe on any solder pad along the suspicious trace and ea&See&erautomatically calibrates itself to the resistance of the defect, within a E milli/ohmJwindowJ$ :ecause the test voltage is a current/limited eight volts, it will powerthrough good diodes to activate shorted components beyond$ %ouch a pad in onedirection or the other and ea&See&er beeps higher or lower and lights the -distance scale to indicate that you>re getting closer or further from the defect$ %heE milli/ohm window allows about to D inches of 4": trace to be chec&ed, thenautomatically re/calibrates itself to a new window as you get closer to the short$:ecause ea&See&er has a range of )ero to 10 ohms, it can locate not Austshorted, but lea&y parts as well$ #nd unli&e your -23, ea&See&er>s uni(ueJfloating referenceJ circuitry doesn>t give up resolution at these higher lea&age

values$ ?nce you>re in the general area of the defect, switch from the #!%? to the?"K position, igh -efinition mode$ %his loc&s the JwindowJ and increasesresolution to 0$1 milli/ohm, so you can pinpoint the location of the defect within a(uarter of an inch, even on multilayer boards with a power plane instead ofindividual traces$ %he currently available ea&See&er 8: - has indicators forJstandard resolutionJ #!%? and Jhigh definitionJ ?"K$%he solder pad where the beep is highest is the location of the defect$


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$mart Twee5ers-

Smart %wee)ers is an ";5'nductance,"apacitance,;esistance6 meter in a set oftwee)ers$ Smart %wee)ers features a uni(ue patented mechanical and electronicdesign that integrates a highly accurate digital multimeter with a built/in high

precision S3- probes and a display$ %his light weight device can be easily held by one hand$ 't is designed for component evaluation on a 4": or a productionline, component testing and sorting of S3- components$ Smart %wee)ersdramatically reduces time necessary to troubleshoot or debug a complex 4":significantly simplifying process of locating a faulty component$

$ome Precautions-

:e careful with your test e(uipment, don>t store meters in extreme conditions5e$g$xtreme hot or cold storage6$ -on>t slam or seriously vibrate the meter, especiallyanalogue meters which have delicate parts inside$

;ead the manuals that come with your different meters$

#void ma&ing measurements that exceed the ma&ers recommendation in any particular setting$

#void ma&ing voltage or current measurements with the meter switched to theresistance setting$

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$chematic Diagrams

Schematic diagrams can really ma&e troubleshooting "- %2s much easier andcan often be found online in service manuals available for download$ 3any times

though, the service manuals will not have that much info and have only partial orno schematics at all$ %his is why it is so important to further your electronics&nowledge and to be constantly studying$ %he more you &now about electronicsand common circuits, the easier it will be for you to recogni)e the circuits in the%2 you are wor&ing on and to (uic&ly see how they wor& and have a good idea ofto start troubleshooting the %2 regardless of whether or not you have a schematicdiagram$ 'f you have a strong understanding of electronics you will be able toanaly)e, troubleshoot and repair any circuit$ 't still never hurts to see whatinformation you can find as the internet has made so much available to the

technician and hobbyist repairer that was not available to us in past so easily$

Bloc Diagrams-

ere is a typical "- %2 bloc& -iagram to help give you an idea of how theywor& from a to )$

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%nderstanding and Testing Resistors

Resistors +n (n LCD TV Power $upply

# resistor opposes the flow of electrical current$ ;esistance is measured in ohms$%he main characteristics of a resistor are it>s resistance value in ohms and it>s

power rating in watts$ Never replace a resistor with a lower power rating than theone removed from the circuit, it is ?K to use one with a larger rating but neverlower$ ;esistor resistance values add normally when connected in series, but addin reciprocal when connected in parallel$

;esistor Schematic Symbols

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Reading Resistors-

;esistors are mar&ed with colored bands to indicate the resistance value$ ;eadingfrom left to right, the first band is the first digit of the resistance value the second

band is the second digit of the resistance value$ %he third band is the the multiplier

and determines how many )eros follow the first two digits, the fourth band isanother important value and that is the tolerance$

%he tolerance is the percent plus or minus that the value of resistance can varyfrom the value calculated from the color bands$ xample, a resistor with bandsfrom left to right of red, brown, yellow and gold would be 10,000 ohms or 10&ohms with a tolerance of L$ Sometimes you will see resistors with five bands, inthis case the first three bands are digits, the fourth band is the multiplier and the

fifth band is the tolerance band$ Some resistors li&e S3- ones for instance willuse numbers instead of bands but the idea is the same$ or an S3- resistor with Dnumbers the first number is the first digit of the resistance value the secondnumber is the second digit and the third number is the multiplier$ So and S3-resistor mar&ed 10D, would have a value of 10& ohm$ #n ; may be seen in thevalue for instance E;7, the ; represents a decimal and in this case the value would

be E$7 ohms$0


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Testing Resistors-

%esting resistors can be done with your -33 or analogue meter$ -etermine thevalue the resistor is supposed to be by using the color bands or numeric code$ 'fthe resistor is burnt or discolored so that you can not read the bands you will needthe schematic diagram for the %2 you are wor&ing on or you will have to use thetechni(ues described in the boo&,


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?nce you &now the value of the resistor you want to test is supposed to be you cansimply set your -33 or analogue meter to the proper resistance range andmeasure the actual value of the resistor$ Cou should get a resistance measurementwith in the tolerance of the given resistor, most bad resistors will have increasedin value or gone open reading ?$$+ infinite resistance$ "harred and burnt resistors

are obviously bad and need replacement$ #lways remove resistors from circuit before testing, as surrounding components may cause erroneous readings$ *attageis not always listed on resistors and is determined by the physical si)e$

Testing Resistor 1n LCD *ain Board

*eter Reading 9:;.< ohms the resistor stated 99= ohms on the side and at >?

tolerance so this as a good resistor


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%nderstanding and Testing Capacitors

Capacitors +n LCD Power $upply

# capacitor is a passive electronic component that consists of two conductorsseparated by a dielectric5insulator6$ *hen a potential difference5voltage6 existsacross the conductors an electric field is present within the dielectric$ %he effect isgreatest between wide, flat, parallel conductors that are very slightly separated by

dielectric$

Capacitor $chematic $ymbols

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"apacitors are widely used in electronic circuits for coupling5bloc&ing the flow of-" while allowing #" to pass6, decoupling5also called bypassing, passes -"while bloc&ing or bypassing #"6, filtering interference, Smoothing the outputfrom bridge rectifiers, removing ripple on the output of S34S power supplies andmany other purposes$ "apacitor capacitance values add normally when connected

in parallel, but add in reciprocal when connected in series

Testing Capacitors-

3ethod one, use your analogue meter set to the x1 ohm range and connect the testleads to the capacitor$ %he meters needle should &ic& up and then return to infinityif it does not flic& or respond reverse the test leads, if it still does not flic& tryagain with your analogue meter set to x10 ohm, x100 ohm, x1& ohm and then

x10& ohm range until you get a response if the meter needle does not flic& whenthe test leads are applied to the capacitor in any setting than the capacitor isconsidered open$ 'f the needle flic&s up and stays at )ero ohms the capacitor isconsidered shorted, also if it stays to any other value other than infinity afterflic&ing it is lea&y$ %his method of testing is fairly old and not the best method$Bust because a capacitor can charge or discharge does not mean it is a goodcapacitor$ Cou can also use your -33 set to the resistance setting to do this test,it should show some reading and then go to ?$$5?ver imit6, and if you reversethe test leads it should do the same again$

*ethod Two-

%he second method for testing capacitors is to use a capacitance meter or thecapacitance setting on your -33, if it has one$ :y placing the test leads of themeter to the leads of the capacitor the meter will display the measured value$

%he value of measured capacitance should be what is mar&ed on thecapacitor5plus or minus the tolerance value6$ 4lease note electrolytic capacitorswill have the value for capacitance for capacitance mar&ed on the side in micro/farads5u6 along with the wor&ing voltage$ 3ost non/electrolytic capacitors willhave their value in a numerical code mar&ed on the side$

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lectrolytic capacitors are the most common capacitors to fail in electronic devicesand one of the most common components you will find failed in "- %2s ingeneral$

lectrolytic capacitors may test fine with methods one and two but can have araised S; which is causing a failure that would be missed by the first two testingmethods$ 'n this case you need the S; meter to find the bad capacitors$ %o usethe S; meter simply place the test leads to the leads of an electrolytic capacitor

and compare the reading5in ohms6 to the one on a chart of typical S; values forelectrolytic capacitors that should come with your S; meter$ 3ost S; meterswill have an S; value chart right on the meter itself$


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Cou can usually chec& electrolytic capacitors in circuit, but ' still recommend

pulling them out of circuit or at least de/soldering and lifting one lead of thecapacitor before testing$

%sing 0$R meter to test $*D electrolytic capacitors on the main board

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Checing 0$R 1! $econdary ilter Capacitor 1n Power $upply Board

%o sum things up the first two methods are great for testing non/electrolyticcapacitors li&e ceramic disc capacitors, etc$, or the first method for testingelectrolytic capacitors to see if they are open , lea&y or shorted$ #lso it doesn>t hurtto ma&e sure the capacitance of electrolytic capacitors is within tolerance$ %hethird method, using the S; meter is the best way to test electrolytic capacitorsand these are the most common capacitors to fail in electronic circuits, caused by araised S;$

@ou can tell this electrolytic capacitor is bad /ust by looing at it# always

replace any pu!!y or "ented electrolytic capacitors# no need to e"en test theme3cept !or curiosity.

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*ore ob"iously bad electrolytic capacitors

$ymbol or 0$R

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Testing Ceramic Capacitors-

Ceramic Capacitors

$*D Ceramic Chip Capacitors

!se method one and two described earlier to test these types of capacitors$

Testing Ceramic Chip Capacitor 1n *ain Board ith Capacitance $etting

1! D**

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*eter Reading in n&nano!arads' =.=>9 nano!arads or >9 pico!arads

%o test the test the high voltage resin coated ceramic capacitors li&e found on thesecondary side of some inverters, you will have to use an insulation tester as thelow voltage output from your -33 or analogue meter is not enough to test thistype of capacitor$ #lso these capacitors will also many times have physical damagethat you can see li&e a crac& in the resin coating or discoloration or burn$

>p A6V Ceramic Capacitors on $econdary $ide 1! (n LCD TV +n"erter

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(n +nsulation Tester

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%nderstanding and Testing +nductors

+nductors +n $econdary $ide 1! P$%

#n inductor also called a reactor, coil or cho&e is a component that exhibitsreactance resisting changes in current flow and can store energy in a magneticfield when an electric current pulses through it$ Since inductors resist changes incurrent flow, they attenuate or


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Testing +nductors-

%esting inductors is fairly simple$ :asically an inductor is a wire coil wrappedaround a core5 some have no core called an air core6 often made of ferrite$

!se your analogue meter set at x1 ohm or your -33 set to resistance setting and place test leads onto the leads of the inductor$ Cou should get some reading,usually very very low ohms your -33 may even show 0 ohms$ 'f you get aninfinite or ?$$ ;eading the inductor is considered open and should be replaced$

Testing +nductor +n LCD TV Power $upply

'f the coil is not open you can also use the inductance setting of your -33 or aninductance meter if you have one or the other and chec& that the inductance iswithin tolerance of the value mar&ed on the inductor$

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+nductor Color Code

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or high @ low loss coils li&e the primary winding of the S34S switchingtransformer you should use a ring tester to chec& for shorts between windings$

4lace the test leads of the ring tester onto the leads of the inductor and chec& the

amount of -s that light up to indicate the rings for the coil you are testing, themore -s the better$ 3ost igh @ coils will light up at least one green -$

Cou should see what &ind of reading you get from various &nown good inductors,so you &now what &inds of readings you should be loo&ing for when testinginductors in "- %2s$

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!nderstanding and %esting %ransistors

# transistor is a semiconductor device commonly used to amplify or switchelectronic signals$ # transistor is made of doped semiconductor material Aunctions,with at least three terminals for connection to an external circuit$ # voltage orcurrent applied to one pair of the transistor>s terminals changes the current flowingthrough another pair of terminals$

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BJT-

:ipolar Bunction %ransistors5:B%s6 are made from three sections of semiconductormaterial, alternating p type and n type resulting in two pn Aunctions, one pn

Aunction existing between the emitter and the base the other existing between thecollector and the base$ :B%s are classified as npn or pnp depending on thearrangement of there n and p type material$

$chematic $ymbol

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$tep : Testing an P4P BJT ith D**

$tep 9 Testing P4P BJT ith D** &$imply Repeat : 9 ith Test Leads

+n Re"erse Polarity or $teps A (nd '

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Cou can also use your analogue meter to test :B%s$ Set your meter to the x1 ohmrange and perform the test in the same manner as with the -33 only instead of avoltage drop reading you will be loo&ing at a resistance reading and the test leadsin the ohms range are reversed in comparison to a -33 the blac& test lead is

positive and the red test lead is negative, but the idea is the same between base and

emitter you should have a low reading in one direction and a highreading5infinity6 in the other direction, same with the base and collector$ Coushould get infinite reading in both directions between collector and emitter in thex1 ohm range$

Testing P4P BJT with (nalogue meter

Testing P4P BJT with (nalogue meter

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Some -33 have a transistor test mode for chec&ing h5beta or gain6$ Cou canuse this setting to test if a :B%s h is within tolerance$

D** h0 $etting

*1$0Ts-

Power *1$0T$ +4 LCD P$%

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%he 3?S% or 3etal ?xide Semiconductor ield ffect %ransistor is acomponent similar to the :B% in the fact that it can amplify or switch electronicsignals$ %he :B% relies on ma&ing a reverse biased Aunction conduct by applyingan electronic signal to the other Aunction$ %he 3?S% or %5ield ffect%ransistor6 is entirely different$ 'n a 3?S% a strip of semiconductor material

either n or p doped between the source and drain is made either more or lessconductive by the presence of an electric charge between the gate and source$

%he 3?S% has three terminals or leads, the gate, source and drain$ :oth nchannel and p channel devices are used in "- %2s$

Special care must be ta&en5S- :racelet etc$6 when handling small signal

3?S%s, because the gate is completely insulated from the source and drain bya very thin film of silicon dioxide$ %he insulation brea&s down at roughly 0/1002depending upon the thic&ness of the silicon dioxide film$

*1$0T +Cs on the in"erter board$

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*1$0T $chematic $ymbol

Testing *1$0Ts-

?nce you have loo&ed up the part number of the 3?S% you want to test onlineor in a parts reference manual or loo&ed at the schematic diagram for the %2 youare wor&ing on and &now where all the pins are set your analogue meter to thex10& range to chec& the 3?S%$ et>s say you are testing an n channel3?S%, put the blac& test lead on the drain pin then touch the gate pin with the

red test lead$ %his will discharge the 3?S%s internal capacitance$ Next placethe red test lead to the source pin while still holding the blac& test lead to the drain pin$ Now ta&e a finger, while still holding the test leads in place, red on source and blac& on drain, and use that finger to touch the gate and drain pin at the same timeconnecting them, the analogue meters needle should move from infinity to aroundthe center position of the meters indicator$ %a&ing the red test lead off the source

pin and placing it bac& on the source pin the needle should still go bac& to themiddle of the meters indicator$ %o discharge the 3?S% lift the red test leadfrom the source pin and touch it to the gate pin, this will discharge the internal

capacitance again and if you again place the red test lead on the source pin and the blac& test lead to the drain pin, the needle on the indicator should not move andgive an infinite ohms reading$ %esting a p channel 3?S% is the same as for ann channel 3?S% only you will reverse the test leads$ 'f all measurements ta&enfrom a 3?S% are low ohms or )ero ohms reading on the indicator and the3?S% will not discharge than the 3?S% is considered shorted$

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$tep : Testing 4 Channel *1$0T

$tep 9 Testing 4 Channel *1$0T

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$tep A Testing 4 Channel *1$0T

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Special testing devices are available Aust for testing 3?S% transistors$

(lternati"e *1$0T Test *ethods-

D0-*1$0T &Depletion,0nhancement Type#' %est !sing an ohmmeter set tothe x 100 ohm scale, measure the resistance between the 3?S% drain and thesource, then reverse the ohmmeter leads and ta&e another reading$ %he readingsshould be e(ual, regardless of meter lead polarity$ "onnect the positive lead of theohmmeter to the gate$ !sing the negative lead, measure the resistance between thegate and the drain and between the gate and the source$ :oth readings should show

infinity$ -isconnect the positive lead from the gate and connect the negative leadto the gate$ !sing the positive lead, measure the resistance between the gate andthe drainM then measure it between the gate and the source$ :oth readings shouldshow infinity$ 'f the 3?S% has a substrate connection, -isconnect the negativelead from the gate and connect it to the substrate$ !sing the positive lead, measurethe resistance between the substrate and the drain and between the substrate andthe source$ :oth of these readings should indicate infinity$ -isconnect the negativelead from the substrate and connect the positive lead to the substrate$ !sing thenegative lead, measure the resistance between the substrate and the drain and

between the substrate and the source$ :oth readings should indicate a lowresistance 5about 1,000 ohms6$

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0-*1$0T &0nhancement Type# The most common type you will encounter'

%est !sing an ohmmeter set to the x 100 ohm scale, measure the resistance between the drain and the source, then reverse the leads and ta&e another reading between the drain and the source$ :oth readings should show infinity, regardlessof meter lead polarity$ "onnect the positive lead of the ohmmeter to the gate$

!sing the negative lead, measure the resistance between the gate and the drain andthen between the gate and the source$ :oth readings should indicate infinity$-isconnect the positive lead from the gate and connect the negative lead to thegate$ !sing the positive lead, measure the resistance between the gate and thedrain and then between the gate and the source$ :oth readings should indicateinfinity$ 'f the 3?S% has a substrate connection, -isconnect the negative leadfrom the gate and connect it to the substrate$ !sing the positive lead, measure theresistance between the substrate and the drain and between the substrate and thesource$ :oth of these readings should indicate infinity$ -isconnect the negative

lead from the substrate and connect the positive lead to the substrate$ !sing thenegative lead, measure the resistance between the substrate and the drain and

between the substrate and the source$ :oth readings should indicate a lowresistance 5about 1,000 ohms6$

Cou should always try and find a data sheet for the 3?S% you are testing because you will find some 3?S%s will have different characteristics that will

ma&e the test readings slightly different$ or instance the 411NK0 has a diode between source and drain, so that when testing you will get a reading in onedirection between source and drain in x100 ohm setting and this is normal$

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%nderstanding and Testing Diodes

Diodes +n LCD TV $tandby Circuit

# diode is a two terminal electronic component that allows electric current to flowin only one direction$ %he word diode is usually associated with the semiconductor

diode which is the most common diode in use at the time ' am writing this$ %hesemiconductor diode is made up of a pn Aunction$

Recti!ier Diode $hown 4e3t To $chematic $ymbol

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$chematic $ymbols or Di!!erent Types 1! Diodes

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Testing The Diode-

!sing your -33 set to the diode test mode, place the blac& test lead on thecathode5mar&ed with a band6 lead of the diode and the red test lead on the anode$

Cou should get a voltage drop reading of between 0$E/0$7$ ;everse the test leadsso that the red test lead is on the cathode and the blac& test lead is on the anodeand you should get an ?$$ ;eading$

'f you get a low reading in both directions the diode is considered shorted and ifyou get an ?$$ reading in both forward and reverse bias directions the diode isconsidered open, in both cases the diode must be replaced$ 3ost commonly diodeswill be shorted$

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$tep : Testing Diode ith D**

$tep 9 Testing Diode ith D**

Testing Diodes ith analogue *eter-

!sing your analogue meter set to the x1 ohm range place the red test lead on the

cathode and the blac& test lead on the anode, you should get a low ohms readingand reversing the test leads you should get a reading of infinity$

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$tep : Testing Diode ith (nalogue *eter $et To 3:= ohm Range

$tep 9 Testing Diode ith (nalogue *eter $et To 3:= ohm Range

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$chotty Diodes-

$chotty Diodes +n LCD TV $*P$

Schott&y diodes also &nown as hot carrier diodes are semiconductor diodes with a

lower forward voltage drop than a standard diode and a very fast switching action$*hen a current flows through a diode there is a voltage drop which as statedearlier is about 0$E/0$72 for normal diodes, but a schott&y diodes voltage drop is

between 0$1 and 0$E2, the lower voltage drop means higher circuit efficiency$%he most important feature of the schott&y compared with the normal pn diode isreverse recovery time, the time it ta&e to switch from conducting to nonconductingand nonconducting to conducting$ Schott&y diodes can loo& very similar to normaldiodes in design$ ?ften they come in a dual pac&age with the two diodes cathodes

being common$

Dual Pacage $chotty

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Testing $chotty Diodes-

?nce you &now the diode you are going to test is a schott&y than you need to useyour analogue meter and set it to the x10& ohm range$ %esting is similar to thenormal diode only you will get a reading in both directions$ %his is a normal

characteristic of a schott&y diode$ %he reading should be full scale deflection withthe red test lead on the cathode and the blac& test lead on the anode, then with the

blac& test lead on the cathode and the red test lead on the anode you will get asmall lea&age reading$ 'f you get two full scale deflection readings the schott&ydiode is shorted and needs to be replaced, if the reading is infinite in bothdirections the schott&y diode is open and must be replaced$ %esting the schott&y inthe x1 ohm range will be Aust li&e testing a normal diode, also note that not allschott&y diodes will give a reading in both directions when set to x10& but Aust beaware that this &ind of diode can have a reading in both directions when measuring

in the x10& setting unli&e a normal diode$

$tep : Testing $chotty Diode +n 3: ohm $etting

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$tep 9 Testing $chotty Diode +n 3: ohm $etting

$tep A Testing $chotty Diode +n 3: ohm $etting

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$tep Testing $chotty Diode +n 3: ohm $etting

ener Diodes-

ener Diodes +n LCD TV $*P$ $econdary side

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# )ener diode is a diode that not only permits current flow in the typical direction but also in the bias direction when the voltage applied is greater than the brea&down voltage called the )ener voltage$ # )ener diode exhibits very similar properties to that of a normal diode except it is specially designed to have a lowreverse brea&down voltage or )ener voltage$ %his is done by heavily doping the pn

Aunction of the diode$ -oping is the process of introducing specific amounts ofimpurities to the semiconductor material for the purpose of changing it>sconductivity$ %he brea&down voltage of )ener diodes can be controlled (uiteaccurately through the process of doping$ "ommon brea&down voltages rangefrom around 1$2 to 002$ ener diodes are normally used as a voltage referenceor as shunt regulators for voltage regulation in smaller circuits because of theirability to maintain a fairly constant voltage drop with a varying current$

Testing ener Diodes-

%esting )ener diodes is best done with a )ener diode tester$

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ener Diode Tester

#lthough another process that can be used is found in this boo&


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"onnect the )ener diode you want to test in series with a resistor to limit currentflow through the testing circuit5the value of the resistor will depend on the )enerdiode and how much current it is rated for6$ %hen connect the ammeter of propersi)e or the current setting of your -33 set to the proper range in series with the)ener diode and resistor$ "onnect the cathode end of the diode to the positive

terminal of the variable -" power supply and the free anode to the negativeterminal of the -" power supply$ %urn on the variable -" power supply andslowly increase the voltage$ No current should flow through the circuit asindicated by the ammeter until the voltage is raised to the brea&down voltage ofthe )ener diode under test$

03ample ener Diode Test Circuit

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%nderstanding and Testing Bridge Recti!iers

Bridge Recti!ier +n LCD TV P$%

%he purpose of the bridge rectifier is to convert #" voltage into -" voltage$

$ymbol or Bridge Recti!ier

# bridge rectifier is an arrangement of four diodes in a bridge configuration andcommonly comes in one integrated pac&age containing all four diodes$ # diode

bridge or a bridge rectifier give full wave rectification$

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Bridge Recti!ier +C

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Testing Bridge Recti!iers-

!sing your analogue meter set to x10& ohms range place the test leads to thenegative and the first #" pin and then reverse the leads, you should show a lowresistance in one direction and infinite in the other direction$ Next do the same test

with the negative pin and the second #" pin the results should be the same$ Nowdo the same tests only with the positive pin and both the #" pins, the resultsshould again be the same$ 'f you find low ohms reading in both directions on anyof these tests then the bridge rectifier must be replaced, also if you get an infinitereading in both directions the bridge rectifier must be replaced$ 'f instead of a

bridge rectifier in integrated pac&age you find four individual diodes in a bridgeconfiguration, test each diode individually and if even one diode is faulty replaceall four$

$tep : Testing Bridge Recti!ier +C

10


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$tep 9 Testing Bridge Recti!ier +C

$tep A Testing Bridge Recti!ier +C

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$tep Testing Bridge Recti!ier +C

$tep > Testing Bridge Recti!ier +C

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$tep < Testing Bridge Recti!ier +C

$tep E Testing Bridge Recti!ier +C

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$tep ; Testing Bridge Recti!ier +C

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%nderstanding and Testing L0Ds

L0Ds 1n LCD TV $tatus Board

#n - or ight mitting -iode is a semiconductor component source of light$-s are used as indicator lights in "- %2s$ %he - is based on thetechnology of the semiconductor diode, when an - is forward biased5turnedon6 electrons recombine with holes inside the component creating an effect calledthermoluminescence$

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%p close Picture o! $*D L0Ds

$chematic $ymbol +n Comparison ith Physical L0D

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Testing L0Ds-

%esting an - is very simple, it will emit light when forward biased and will notemit light when reverse biased$ 'f an - does not light when forward biased thenit has gone open circuit and must be replaced$ %o test, set your analogue meter to

x1 ohm range$ 4lace the red test lead on the cathode pin this side is indicated by aflat spot on the plastic pac&age or a line on S3- pac&ages, the anode side will nothave the flat spot$ *hile the red test lead is on the cathode touch the blac& probeto the anode pin and the - should light, remove lead (uic&ly after - lightsso as not to damage it$

Testing $*D L0D 1n LCD TV L0D,$tatus Board

'f you reverse the test leads the diode will not light$

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%nderstanding and Testing $witching

Trans!ormers

$witching Trans!ormer +n LCD TV P$%

Basic Trans!ormer $chematic $ymbol

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Switching transformers are found in the S34S of "- %2s5%he high voltagetransformers on the inverter board are also a type of switching transformer that wewill discuss later6$ %he function of the switching transformer is to convert a

voltage applied across it>s primary winding into a lower or higher voltage acrossit>s secondary windings depending on the amount of turns in the primary andsecondary windings of the switching transformer$ Switching transformers arerobust components and rarely brea&down, and when it does it will normally causecomponents in the primary side of the switching transformers circuits that driveit>s primary to blow+fail, as well and most li&ely blow the main fuse$ %he mostcommon failure is a shorted primary winding$ %he secondary windings seldomhave issues in the "- %2 S34S due to the fact that they step down voltage andthe secondaries have very few windings, %he primary however has many winding$

%o test the primary winding of the switching transformer use a ring tester$ ocatethe primary winding pins by first following the trace from the positive pin of thereservoir capacitor will lead you to the first pin$

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Next follow the trace from the power 3?S%+s source to the next pin of the primary winding$ 4lace the test leads of the ring tester to these two pins$ 3ostswitching transformers will light up four to eight -s, of course if you can,chec& your reading against that of &nown good switching transformer that is thesame exactly as the suspected one under test, of course this normally is not

possible, so if you only light up one to two or no -s it is most li&ely that theswitching transformer has shorted windings and needs to be replaced$ 'f theswitching transformer tests bad always remove it from the circuit board and testagain to be sure$ 'f it tests good out of circuit suspect other failed components inthe S34S perhaps a shorted secondary side diode$ 'f a switching transformer isfound to be bad you may have trouble finding an exact replacement and you mayhave to find a company or person online that will rewind it for you

or you can attempt to rewind it yourself with instructions found online$ Cou can

also chec& switching transformers for an open primary winding although it is not acommon failure$ Set your -33 to the ohms setting or your analogue meter to x1ohm range$ "hec& for a low ohms reading across the primary winding$ 'f thereading is ?$$ ?r infinity than the winding is considered open and the transformermust be replaced or rewound$

Cou can also chec& the secondary windings to ma&e sure they are not open and ifyou have another of the same switching transformer to compare with you can ringthe secondary windings as well although because they have less windings they will

not light up as many -s, even only one - or none and this is normal$ 'f youget no rings on the secondary windings you can also chec& them with an S;meter to compare with another transformer, since the windings have reactance theywill give high S; reading on the S; meter, if you get )ero ohms on the S;meter this could be a sign of shorted secondary windings$ #nother test is to setyour analogue meter to the x10& ohms range and place one test lead on a pin of the

primary side and the other lead touch to the pins on the secondary side$ Cou shouldnot get any reading between the primary and secondary windings$

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Checing or 1pen Primary inding +n $*P$ $witching Trans!ormer

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%nderstanding and Testing 1pto-+solators

1pto-isolators +n LCD TV $*P$

#n opto/isolator also called an opto/coupler or photo/coupler is a component thatallows a signal to pass from one circuit to another but allows the two circuits toremain electrically isolated$ %he most common opto/isolator which comes in '"

pac&age consists of an - which shines onto the base of a photo/transistor,usually an npn transistor$ # signal is applied to the - which then shines light

that is varied in brightness with the same amplitude as the input signal$ %his lightlands upon the photo/transistor which passes the signal onto the next circuit$

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Testing 1pto-+solators-

!sing your analogue meter set to the x1 ohm range test the - side of the opto/isolator$ *hich will be found be loo&ing up the part number online or referring tothe "- %2s schematic$ # common opto/isolator found in "- %2s is the 817type for instance the 4"817$

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*ultiple Pacage Types

4lacing the test leads on both pins of the - side of the opto/isolator and thenreversing them you should get a low ohms reading in one direction and infinitereading in the other$ 'f you get a low ohm reading in both directions the - sideis shorted and the opto/isolator needs to be replaced$ 'f you get an infinite readingin both directions, the - side is open and again the opto/isolator must bereplaced$

Next you must test the transistor side of the opto/isolator$ Some opto/isolators willhave six pins in which case the three pins that correspond to the transistor side ofthe '" will base, emitter and collector and on the - side the three pins will bethe anode, cathode and one pin with no connection$ 'f you have a six pin opto/isolator, refer to the section of this boo& on testing transistors to chec& thetransistor side$ 'f you have a four pin opto/isolator which ' find is most common in"- %2s, then set your analogue meter to the x10& ohm range and place the test

leads on the two pins of the transistor side which will be the emitter and collectorand then reverse the test leads$ Cou should get a high ohm reading with the testleads in one direction and an infinite reading in the other direction$

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$i3 Pin 1pto-isolator

'f you get a high ohm reading or low ohm reading in both directions the opto/isolator must be replaced$ Now set the meter to x1 ohm range and place the testleads on the emitter and collector in both directions again, now you should getonly an infinite reading in both directions, otherwise the opto/isolator must bereplaced$

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$tep : testing L0D side

$tep 9 testing L0D side

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$tep A testing transistor side

$tep testing transistor side

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%nderstanding and Testing Voltage Regulators

Voltage Regulator +Cs on LCD TV *ain Board

# voltage regulator is an electronic circuit designed to automatically maintain aconstant output voltage regardless of fluctuations in input voltage or current drawfrom the load5to an extent6$

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Testing Voltage Regulator +C-

%o test the voltage regulator '" you must chec& it in circuit with the %2 plugged inand or power on to the "- %2$ 4ower the %2 on and set your -33 or analoguemeter to the proper -" voltage setting$ 4lace your blac& test lead to cold ground

and carefully place your red test lead to the output pin of the regulator, usually pinthree on many voltage regulators, li&e the 3780$ ;emember to always loo& upyour part numbers for the part you are testing if needed so you can be sure to test it

properly$

Typical L*E;=> Pacage

Now you should expect the output voltage to be within tolerance of the regulatorsspecified voltage$ So for an 3780 you should expect about $1/$92 -", if youmeasure a low voltage li&e say 12 you should turn the %2 off and unplug it thenlift the output pin of the regulator from the circuit$ %hen power the %2 on againand retest chec&ing the voltage right on the lifted pin, 'f the voltage is bac& toaround 2 again instead of 12 then the '" is most li&ely good and you shouldsuspect shorted components in the circuit after the regulator that are pulling downthe voltage$ 'f the voltage is still low then the regulator is most li&ely bad andneeds to be replaced5granted the input voltage is good6$ 'f you measure ?2 on theoutput and even in the case we Aust discussed you should also chec& the voltage onthe input of the voltage regulator and ma&e sure it is at least the regulation voltage

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Checing +nput Voltage to Regulator

Checing 1utput Voltage rom Regulator

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%nderstanding and Testing $witches

Typical Tactile $witch ound +n LCD TVs

# switch is an electronic component which can brea& a circuit or divert current

from one part of a circuit to another part$ %he most common type of switch youwill see in "- %2s is the tactile switch or


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%esting tactile switches and any switch in general is very simple$ Set your -33to the continuity setting or your analogue meter to the x1 ohm range and place thetest leads on to pins on opposite sides of the switch5polarity does not matter6$ Coushould get a reading of infinity$ Now while still &eeping the test leads on the pins,depress the button and the meter indicator should give a low or )ero ohms reading

and when you release the button the indicator should return to ?$$ or infinity$4lease note this is only for testing single pole single throw, normally open or


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%nderstanding and Testing uses

use +n LCD P$%

Pico uses 1n LCD TV +n"erter Board

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# fuse is an electronic component that is used as a sacrificial device for overcurrent protection$ 't contains a wire or strip that melts when to much currentflows though it, which interrupts the circuit that it is connected to$ # fuse isdestroyed by excessive current so that further damage or inAury is prevented fromoverheating or fire$ #lways replace a fuse with the exact same value, type and

rating as the one removed from the circuit$

$chematic $ymbol or use

Testing uses-

Set your -33 to continuity setting or your analogue meter to x1 ohm range$4lace the test leads the terminal caps or leads of the fuse5polarity does not matter6,you should get a very, very low reading or )ero ohms$ %his is the characteristic ofa good fuse$ # bad fuse will give a high, ?$$or infinite ohm reading$ Cou can alsonormally visually inspect glass fuses and see they have blown, or the metal striphas Aust opened$

Testing ( use

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Testing ( Pico use

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$ome Testing Tips

/#lways test components with a meter that is &nown to be good, with fresh batteries installed$

/' suggest removing components from the circuit before testing$ ?ften surroundingcomponents in the circuit cause erroneous readings to occur$ #t least lift+removeone lead from the circuit for most components$

/earn how to test all electronic components and practice testing them so you canfeel confident in yourself when testing components$ #gain ' highly recommend the

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%se!ul ormulas

%hese are Aust examples of the basic and most commonly used formulas inelectronics$ Cou should &now %hese by heart$ %here are many more that you

should study and learn as well if you plan to further your understanding ofelectronics$ %hese formulas are to be used for -" circuits or resonant #"53eaningvoltage and current are in phase and that the circuit 'mpedance is e(ual to thecircuit resistance6 circuit calculations$

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)ow To Disassemble (n LCD TV

irst start by laying a thic& soft blan&et out on a table large enough to lay the faceof the "- %2 on$

Lay The LCD TV 1n +ts ace

Next remove all the screws from the stand and remove the stand$ Next remove allthe screws from the bac& of the %2, it help to have a cup to &eep all the screws in$

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;emove the bac& and set it aside$ Now you will have full access to the4":s54rinted "ircuit :oard6$ %o remove a 4": for component testing or forreplacement, simply disconnect any cables going to the board from theirconnectors$ abel them if necessary$

03posed PCBs

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Next remove all the screws that hold the 4": to the %2$ %he board should nowcome loose$ Cou may now test or replace components on the board youremoved5remember if you remove the 4S! the first thing you need to do is todischarge the reservoir or primary side filter capacitor6$

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Voltage Test Points

arningFFF

:e careful when ta&ing voltage measurements$ #lways an isolation transformer$

;emember when ta&ing measurements on the primary+hot side of the S34S usethe corresponding primary side ground5hot ground6 and when ta&ingmeasurements on the secondary+cold side use the secondary5cold ground6$

+solation Trans!ormer

Bridge Recti!ier-

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4lug the "- %2 in and locate the #" pins of the bridge rectifier mar&ed by awavy line5this is the #" symbol6$ Set your -33 or analogue meter to the proper#" voltage setting$ Now place your test leads against the #" pins of the bridgerectifier$ old them tightly and carefully in position be sure not to slip and shortanything with your test leads$

Placing Test Leads on (C Pins 1! Bridge Recti!ier

Cou should get a reading of around 110/10 volts #"5!S#, in some othercountries the voltage may be different find out the mains in your country and this

is what you should expect6 'f you get )ero volts then chec& in the circuits beforethe bridge rectifier, could be bad components in the 3' circuit, :lown main fuse,

bad #" cord, electrical receptacle has no power, bad components in passive 4"circuit if %2 uses this type of 4", bad solder connection in circuits before or at

bridge rectifier etc$

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Reser"oir Capacitor,Primary ilter Capacitor-

?nce we have confirmed that the bridge rectifier is receiving an #" input at the proper voltage we can now expect to find a -" voltage at the pins of thereservoir+primary filter capacitor$ 3a&e sure the %2 is plugged in$ Now set your

-33 or analogue meter to the proper -" voltage setting place your blac& testlead to the negative pin of the reservoir capacitor, next place the red test lead onthe positive pin of the reservoir capacitor$ :e extremely careful not to accidentallyslip and short the pins of the capacitor together$

Testing Voltage (t The Reser"oir,Primary ilter Capacitor

Cou should get a reading of about 10/102 -"5!S#, 'f active 4" is usedexpect D0/E0026$

'f you get the right reading then move on to the next voltage test$ 'f you get )ero orvery low voltage chec& the surrounding circuits components, loo& for bad solderconnections crac&s in the copper trace, unplug %2 then remove and test the bridgerectifier etc$

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Power +C-

irst you must loo& up the part number of the power '" you will be testing the positive supply voltage pin of$ ?nce you locate the positive supply voltage pin of

your power '", set your -33 or analogue meter to the proper -" voltage range$4lace the red test lead to the positive voltage supply52cc6 pin and the blac& testlead to hot ground5reservoir capacitor negative pin6$ ;emember the %2 needs to

be plugged in$ Cou should get a reading that corresponds to the proper voltage forthe power '" normally between 1/02 -"$ 'f you get the correct reading you canassume all components up to this point must be good5bridge rectifier, fuse, 3'ilter circuitry, start up circuit, etc$6$ 'f you can>t find the necessary information foryou '" you can always s&ip to the next voltage test for this same reason$ 'f thereading is low or )ero volts the most comm

lcd and tv repair guide

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