m3 projector teardown

8/10/2019 M3 Projector Teardown

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M3 Design, Inc. 2010 Page 1 of 18

M3 Design Product Teardown

Dell 2300MP Video Projector

Why do the product teardowns?

Part of the product development process is to apply knowledge gained from prior experience

during the concept development and design phases. Some experience comes from actively

designing something in the past while other experience is gleaned from more indirect

sources. It is this indirect product development experience that we gain via product

teardowns.

Teardowns are different from reverse engineering

Reverse engineering is nothing more than figuring out the design and manufacturing

methods of a product, typically for copying. Conversely, M3 Design views product teardowns

as ways to gain insight into the design to become better product developers. We focus on"why" questions.

Why did the designer make the choices they did?

Why were specific construction techniques chosen?

Why were certain features included and others left out?

Why was the particular design approach chosen?

This serves to gain more in depth understanding into the product's design rather than a

superficial once-over.

How does M3 Design approach product teardowns?

Our teardown process is a rigorous approach to carefully catalog the products

deconstruction in both pictures and written descriptions. This procedure serves two

purposes:

1. It forces the deconstruction team to carefully investigate the product pieces and

learn as much about the design details as possible.2. It provides a detailed record of the process for future reference by other designers.

The end result of this meticulous process is the beneficial expansion of applicable knowledgeregarding product designs. We employ the lessons and insights garnered from these

teardowns during brainstorms, design, prototype development, and troubleshooting. Thismethod of obtaining indirect product development experience is just one of many important

tools that sets M3 Design apart from other product development firms.


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OverviewM3 has video projectors in all of its conference rooms so it was only a matter of time until

one went belly up. Our patient for this report was a Dell 2300MP front projector withTexas Instruments DLP technology. The Product Teardown team took this opportunity toseek the inner mysteries of yet another product we largely take for granted; at least until it

wont light up. When we have customers in. Dang.

External ConstructionThe projector body was a painted molded shell, held together with snap fits and screws. A

separate cover, accessed by two screws, defined the projector lamp area. There werenumerous vents on the product, for cooling the high-temperature lamp and system optics.

The rear panels had plenty of I/O connection options for both computer presentations and

for use as a TV monitor.

Overall product view

Front IR sensor

Illuminated user buttons


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Rear I/O Connections

Systems

A block diagram of the major projector systems is shown below with the connections

between each. These systems will be explained in more detail in.

Main PS

Lamp Driver

FansControl Board

+ I/O

Sensor

DLP Chip

Optics / Light

Chamber

Projector Lens

Light

Filter

Projector

Lamp

Rear IR sensor


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Internal stuff

Some of the more interesting internal items encountered were a temperature sensor with

alarm and control output with hysteresis, a thermal cut-off switch mounted near the lamp,

and two IR sensors for a remote control. One IR sensor was on the front of the case andthe other on the rear, allowing for more flexibility in locating the projector and controlling it

via remote control.

Internal view of projector (main control board pulled away)

Optics

DLP Board

Fans

Lamp driver

Lens

I/O Board


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The main user buttons consisted of a monolithic plastic flexure, molded from clearPolycarbonate. The flexure was painted silver on the outside (to match the projector case

color) and black on the inside. LED light from a PCBA with small switches shone throughareas on the buttons, defined with either a mask during paint or laser-etched after painting.The buttons illuminated when the projector was powered on.

Black tape was found around any seam where light could leak out. Some areas included the

IR sensor module, gaps in the external shells, and areas around the optics.

Backside of user buttons Front side of user buttons


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Lamp and Power

Since the most frequent service item is likely to be the lamp, the system was optimized for

accessing the lamp cavity. The main electrical interface to the 200-Watt lamp was a two-conductor connector for power. Separate screw connections held the lamp assembly in

place. There were numerous light baffles in the housing to contain the light and ensure that

there were no leaks into other areas of the projector.

There was a switch on the unit to ensure that the lamp power was cut whenever the door

was open a critical safety feature. The cover was made from Noryl, a high temperature

(Tg>100C) plastic, which makes sense considering the high thermal output of a projector

lamp. A conductive coating was applied to the inside surface of the cover and the plasticprojector body, presumably for EMI shielding purposes.

View of lamp cavity cutoff switch at top

Cutoff Switch


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Lamp power connector left side of cavity

Lamp powerconnector


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Power Supply and Lamp Driver

The main power supply took in AC power and distributed AC and DC power to the main

control board and the lamp driver. The lamp door safety switch connected directly to the

main power supply to cut power to the lamp driver when the door was opened. Doing thiswith hardware was simpler and more reliable than monitoring an input sensor and

controlling a relay to turn off the lamp. There may also be a product safety requirement thatdrives this approach.

A separate lamp driver was required to ignite the high-power lamp and to control power tomaximize lamp life. The lamp driver had an I/O connection to the main control board for

handling lamp behavior and to monitor lamp life.

Lamp driver

Main power supply

Lamp power

connector

Connector to lamp

driver supply

Input from main

power supply


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Control Board

The main control board handled all of the sensor inputs and control outputs. There were

various microcontroller chips throughout, including a DLP processor chip. The board

connectors were color-coded to aid with assembly of the various sensors such as opticaldetection for color wheel motor speed, temperature, and IR remote control. Outputs

included fan control and connections to the main power supply and lamp power supplyboards.

Main controller board installed (I/O board is underneath)

Controller board: colored connectors at bottom edge


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Optics

As expected, the optic subsystem was complex and highly engineered. It was also verydensely packaged as noted by some of the beam shaping lenses having a corner notched for

proper fit. Take a look here for some information on the basics of DLP technology:

http://www.dlp.com/technology/how-dlp-works/default.aspx .

This matches what was found in the Dell projector. Based on how these optics were

packaged it is likely that they were an entirely separate sub-assembly built in another

factory, allowing the optics manufacturer better control over their intellectual property.

Optics top side installed in projector

Lamp Cutoff Switch

DLP Board


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Optics bottom side

Light Path

DLP Board


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Light filter

The light filter consisted of a disk with red, blue, and green color filters with a fourth clear

filter. The filters were laid out like slices of a pie. The purpose of the color wheel is to

cause red, green, and blue colors to shine onto the DLP chip, coordinated with the switchingof the DLP mirrors to project the correct color image. Of interest was that the filter sizes

were not the same red was the largest, followed by blue, and then green. Clear was thesmallest. The reason for this is that the human eye is most sensitive to green light,

followed by blue, and lastly red. Therefore the red must be on longer for our eyes to

absorb enough light to perceive that red has the same intensity as blue and green. Themotor was a simple blushless DC motor. A photo sensor aimed at a black piece of tape on

the motor rotor provided the speed feedback to synchronize the color wheel position withthe DLP optics chip mirror switching.

Filter motor: note black tape for sensor

Black tape


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Fans

As expected, cooling fans were used near the optics. One axial type moved air from near

the lamp. A second centrifugal fan pulled air from underneath the projector and vented it

into the optics path chamber. Both fans had rubber housings around their plastic bodies toattenuate any vibrations to the sensitive optics and prevent acoustical noise.

Optics housing

A cast magnesium housing made up the optics support chamber. It was a rather complex

monolithic part that precisely held the beam-shaping lenses, mirrors, and filters. One piece

in the optics path was a tube of mirrors which the team surmised acted as a light pipe to

help to precisely point the light before entering the shaping lenses. The tube was positioned

using two small screws that were epoxied in place once the final adjustment was performed.

Spring fingers held the light tube against the optics housing mounting features. This is

common practice in precision-engineered systems to provide exact-constraint location.

Exact constraint is important to use anywhere thermal expansion could be a problem, as the

parts will distort into unexpected shapes if they cant expand.

Cast optics housing Tube of mirrors and spring fingers


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Light Chamber

The chamber that the DLP chip was held in was painted flat black to reduce light scatter and

any unwanted reflections into the image. One curious component was an L-shaped black

heat sink mounted to an opening in the side of the chamber and isolated with an elastomergasket. After some head scratching, a team member realized its function. This component

was likely a beam dump where light could be focused by the DLP chip and prevented fromexiting through the projection lens. When a projector turns off the image without turning

off the lamp, this is where all the light goes since it isnt released out of the projector. A

heat sink was necessary, as the incident light will heat up the black surface. It was isolatedto keep the heat from affecting the rest of the light chamber.

Light chamber (black) next to PCBA (DLP board)

Light chamber


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Beam dump heat sink and elastomer gasket

Projection Lens

The two projection lens components consisted of focus and zoom elements. The zoom

moved a lens pair within a barrel housing and the focus moved the final lens relative to thelens pair. The zoom was accomplished with a metal rod moving in a barrel cam to move the

lens axially.

Focusing lens note zoom lens barrel cam

Heat sinkGasket


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DLP Chip

The final system was the DLP assembly itself. This is the optical chip that controls an array

of microscopic mirrors to reflect an image into the projection optics. A large heat sink was

mounted to the rear of the chip to carry away the large amount of heat caused by thefocused light onto the chip, not unlike the beam-dump heat sink. The chip was mounted to

a ceramic carrier board with signal pads on the backside. A plastic socket with spring fingersignal pads was the interface between the chip and the controller PCBA.

DLP Chip in socket

Heat sink on back side of DLP chip


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An aluminum clamp held the chip/socket/PCBA sandwich together and secured everything

with rubber-isolated screws. This was likely done to allow some compliance between all theelements and allow varying component tolerances without damaging parts during assembly.

Clamp to hold everything together

Plastic socket with signal spring fingers

Rubber-isolated screw (1 of 4)


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Summary & ConclusionsThe projector was a complex product with a large number of densely packaged parts. While

a monolithic control board (for example: projector controls and DLP processing) could haveeased space constraints, the distributed system likely sped product development. Thisapproach allows different teams to focus on the various sub-systems and optimize them in

parallel. It is also likely that separate companies developed the DLP chip control and optics

sub-assembly, as these systems require specialized expertise.

In order to create such a product, the development team would require a systems approach

to manage the various areas of expertise: plastic molded parts, PCBA/hardware

development, firmware, optics, cooling, and motor control. The systems approach is

extremely important, as this broad range of technology disciplines tend to have vastly

conflicting requirements and constraints.

Exploded projector view!

m3 projector teardown

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