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Thread: Running the XJ-A140 With Missing Diodes

  1. #1
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    Default Running the XJ-A140 With Missing Diodes

    I finally got a hold of a new projector, and was able to resume experimentation. Due to the large amounts of pollution in the existing threads, I have created this thread devoted specifically to running these projectors with 1 or more missing diodes, please keep any other discussion in other threads.

    Current Progress:
    I first removed the diode array, unsoldered 3 of the 4 diode banks, and attached wire to each of the 3 banks. Note, there is a small surface mount component on each of the outer banks, this is a 10k NTC thermistor and removing it will cause an overheat error on the projector. It is important to leave at least one of them in good contact with the diode array, so the the computer can detect possible overheat conditions.
    Click image for larger version. 

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    After this was done, the connections were insulated, and the array installed back in the projector. Space is tight, so don't use excessive tape, and keep in mind that the heatsink gets HOT which will cause most adhesives will loose their stick, so plan accordingly.
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    Finally the wires were connected to power resistors (its messy/undersized, I used what was laying around), and the projector was powered up.
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    Findings:
    *Removing diodes does not adversely affect the uniformity of the output, I removed 18 diodes from my projector, leaving a single string of 6 at one end of the diode array, and the uniformity of the output did not change appreciably. For reference, the diodes are arranged in 4 groups of 6 diodes, in groupings 3 diodes 'tall' and 2 diodes 'long' stacked next to each other to form a 3x8 array of diodes.

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    note - don't trust this picture too much, it is testing my camera more than it is the projector. The white balance looks a bit better in this picture than in real life, however the grays actually do look gray in real life, not purple/brown as in the image.

    *Despite the fact that the 445nm diodes are the workhorse of the projector, it is possible to remove large numbers of them without throwing off the color balance. I removed 18 diodes from my projector, and the output is still acceptable (see image below). The output does look a little yellow, but I have seen properly tuned projectors that looked worse (this is due to the fact that the human eye's color response fits a power law, so the 75% decrease in power only looks ~20% dimmer)

    *The projector's power supply actually has a large compliance voltage range, and works with voltages as low as 20V (as opposed to the 30v typically encountered in operation). This means that you can remove 2 diodes per string (that is a total of 8 diodes) without making any changes to the projector, simply remove up to 2 diodes per string and short across the pads.

    *This also means that you can remove an entire string, and replace it with a simple resistor. Resistances as low as 14ohm work, but I recommend a 15ohm resistor in case different projectors have slightly different compliance voltages. This resistor must be capable of dissipating at least 20W of power, I recommend getting at least a 25W resistor to play it safe. Something like the TBH25P15R0JE ($5 a piece) would work well if it were mounted to the heatsink internally. This might require some creativity/modifications, and in any case I hope to eliminate the need for this resistor altogether (see future work) so I am not perusing this too much further.

    *Due to the pulsed nature of the output, you must be careful to keep the inductance of the dummy resistor low. In my testing I had appropriately 10in^2 of loop area, and while the projector did power up I was able to hear the 75Hz buzz on my radio! This can be done by twisting any leads together, and using a low inductance (NOT wirewound, thick film or the likes) resistor.


    Future Work
    *It looks like it will be possible to disable the voltage sensing entirely and just short out unused channels, I hope to investigate this further. If anyone would like to donate a diode driver board I would be happy to try and modify it. I have a simple schematic drawn up if you would like to perform the mod yourself and report back as well, but it will require cutting traces and rerouting signals. Those who get squeamish at taking a razor to their $800 projector need not apply!

    *I am also investigating how to dim the red led, the current plan is to add a simple resistor in parallel which will divert some current through the resistor, and cause the LED to dim. I hope to try this tomorrow, I suspect that a ~0.25ohm 25W resistor will do the job, although it will get hot! Again, it would be nice to trace down the current sense line inside the projector, I hope to investigate this route as well.

    One Request
    I encourage everyone to perform this type of mod on their projector, however I would like to politely ask that you do not offer this as a service commercially.
    If someone would like me to perform the remove 2 diodes from your projector I would be happy to, simply send my your diode array (you pay shipping both ways) and an I will remove up to 8 diodes from your projector, I only ask that you let me keep one of the diodes I remove for my time. Alternatively, I will perform the mod for $40 and you can keep all of your diodes.
    Obviously there is no way for me to enforce this request, but it is a way to help recoup the time I have invested in reverse engineering these projectors. Needless to say, if people do begin ripping off my findings for commercial gain I will stop publishing them.
    Last edited by krazer; 07-25-2010 at 02:22. Reason: fixed pictures

  2. #2
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    nice work.

    I'll run it by dave, if he's okay with it, we may have a driver board to send you.
    Now proudly stocking and offering the best deals on laser-wave

    www.lasershowparts.com
    http://stores.ebay.com.au/Lasershow-Parts

  3. #3
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    Fantastic work Krazer,
    I know some holography folks will be happy!
    I always thought this was possible going down this route, but never had the time to go out and get some beefy resistors to test with.

    Also, I have *buckets* of spare parts of every kind, thermistors, screws, array ribbons, panels etc.. you name it, I've got boxes full of them.
    I also have many projectors I want to get rid of for a modest cost; most have all the parts still in (except the diodes).
    Please PM me should anyone be interested. Massive discount for anyone wanting several units, or you'd be an absolute godsend if someone wanted to buy the LOT!!!
    - There is no such word as "can't" -
    - 60% of the time it works every time -

  4. #4
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    How did you manage to unplug the array flat cable from it's connector without destroying it?I never got a reliable connection again once I removed it.

  5. #5
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    Quote Originally Posted by decix View Post
    How did you manage to unplug the array flat cable from it's connector without destroying it?I never got a reliable connection again once I removed it.
    Lift the black flap...
    - There is no such word as "can't" -
    - 60% of the time it works every time -

  6. #6
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    So...from now on be very cautious when buying casio projectors second hand.
    Most of the diodes could be missing !


  7. #7
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    Did the current into the remaining diodes change appreciably after you removed the other sets and put in 15 ohm load resistors?

  8. #8
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    Thanks everyone for the driver board offers, hopefully Aijii will come through, if not I might look into getting them shipped in from the UK from briggs.

    @decix, as briggs noted, you simply need to lift the little black flap and you can 'easily' slide the connector in/out. Easily is in quotes for a reason, it takes a bit of practice to get them properly lined up, but after you get it aligned in square it will slide in with very little resistance.

    @drlava, I did not measure the current directly yet, but the current in the resistors was the expected 1.44A peak as measured from a projector with the diodes still in it. The driver board has 4 completely independent current sources (separate controller, etc), so changing one channel is not expected to affect any other channel.

    In the mean time, I have been documenting the various boads in the projector, so far I have been storing my findings in a text file which can be found here. All line items with a * on them mean that I have found the datasheet online, if you need it let me know I can try to give you a link. I am working on updating my webpage with this information and some information on the optics and whatnot, so unless you need it immediately I should have them all linked by next week. If anyone wants to try and figure out what all of the top codes surrounded in question marks are for, be my guest I suspect that a lot of them are from rohm, but manufactures really don't have a good system of identifying parts based on top code in place.

    A few comments/interesting facts:
    *The fan controller board has a connector that can be accessed from the outside of the projector by removing a white sticker. Perhaps some kind of debug interface?
    *The fan controller board is just strait forward implementation of the EMC2305 SMBUS (I2C) penta fan controller, which could be easily used outside of the projector under control of a microprocessor. It would also be possible to use a microprocessor to emulate the controller and just return a 'yes all fans working' for projectors that are running without the fans, or to make an interceptor that runs the fans at a lower speed when there are less diodes in the projector.
    *The diode board wasn't so easy, and has a full on 16 bit microprocessor and a CPLD (think watered down FPGA) on it, however I believe that it conforms to a spec outlined in the TI documentation for the DLPC200 DLP system controller.
    *The DLP chip is a DLP5500 0.55" XGA DMD, which is currently available from TI in a dev kit for $2500
    *There is a triple a axis accelerometer on board for the automatic keystone correction. It looks at which way is 'down' and adjusts the keystone correction accordingly. It actually works pretty well!
    *There is both a serial (RS232) and 2x usb interface available through the back of the projector. One of the USB is routed directly to the DDP2431, and I believe that it can be used to control the chip directly (although this may require a custom firmware upload). The other usb appears to be routed to an unpopulated chip, and I suspect the other serial is routed to the microprocessor although I have not confirmed this.

  9. #9
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    Wink

    Quote Originally Posted by -bart- View Post
    So...from now on be very cautious when buying casio projectors second hand.
    Most of the diodes could be missing !

    This is exactly what I was thinking.
    The general public may never notice it!

    I'd directly contact the seller and get a guarantee.

    What a way to get a new tv setup and some cool
    diodes!

    O.P. nice thread!

  10. #10
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    Hahaha, great. Does it save color balance settings permanently even after power off?

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