(Topic ID: 110004)

Williams DMD driver board causing image on DMD to be shown 2 1/2 times

By kbliznick

9 years ago


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  • 12 posts
  • 4 Pinsiders participating
  • Latest reply 9 years ago by thedefog
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#1 9 years ago

Have a bad DMD driver board for a Williams IJ. Power supply on it works fine, but there is a logic problem with it that I haven't see before. Truth be told the only logic problems I have fixed on these boards is just the RAM and I already replaced it so that's not it.

Definitely not the ribbon cables as I already tried another working board in the game with good results.

So it shows a blurry image that is repeated 2 1/2 times across the width of the screen. The height looks like is it too short but it doesn't look like the image is repeated vertically.

Anybody seen this before? Usually I would just toss out a completely dead DMD driver as they are pretty cheap, but this one is clean with low mileage on the power supply and the screen is showing something. I believe this one went bad while being hotplugged into the game (cables connected/disconnected with the game on.

I was hoping it was going to be the RAM, but it wasn't.

#2 9 years ago

Double checked the voltages coming out of the board

4.7V
12V
66V
-99V
-118V

The gap in the two high voltages is a little larger than 12V but wouldn't think this would cause the issue.

The height is correct.
The screen does not roll or anything else typically power related.

Thanks
Kris

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#3 9 years ago

The image at the far right is at the correct height, the one in the middle looks like it's shifted down a line and the half image at the far left looks to be shifted down two lines.

#5 9 years ago

Strange question, but did you try a different *display*?

#6 9 years ago

Yes, tried in another game with similar results.

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#7 9 years ago

hsync is not being calculated properly. Could be a bad ribbon cable. Swap the ribbon cable first. If that doesn't do it, it could be faulty logic that deals with the timing/division.

#8 9 years ago

Was also thinking that possible a crystal is sending out wrong clock (Hz), but don't know enough about how the DMDs are driven, so.. ignore me.

#9 9 years ago

No xtal on WPC DMD boards. This issue is most likely on the DMD itself. Then the DMD board, then MPU. But I'd start with the DMD, checking for cold solder joints, bad pins, connectors and whatnot. Once that is ruled out, we can check some things from there.

#10 9 years ago

This is definitely on the DMD driver board.

Tested another known working DMD driver in this game and the problem is gone. Tested the bad DMD driver in another game and problem followed it. Thus not a problem with the ribbon cables or the DMD or the MPU.

#11 9 years ago

I had the same problem on a T2. I went through all the logic chips on the board using a multimeter on the diode setting and checking every pin to ground. One the chips had one voltage that was a little off from the same pin on the other similar chips ( like 0.2 volts different ). I replaced that chip and the DMD driver board worked great since then.

There are a lot of chips to test and many pins on each chip to write down the voltages so it is a tedious process, but the result was very rewarding to have found and fixed the problem myself.

I do not remember the exact chip that was bad but chances are yours would be a different chip anyway so you will have to go through the process.

This is the process I used except no pins were shorted, I just noted one logic chip was different on one pin than the rest of the same part number logic chips (it read 0.3 when the other read 0.5):

"To test chips, the ground leg of the chip in question will need to be known (that's why we went through the "short course on logic chips" above). Then put the RED lead of the DMM on this ground leg. Yes I know, it sounds weird. "Why the RED lead on the ground leg? Isn't that backwards?" Backwards or not, that's how to do it. With the red lead on the ground pin, check all the other pins (except for VCC, which is the chip power pin) with the black lead of the DMM. Again .4 to .6 volts should be seen for each leg. If a different value is seen, chances are the chip is bad. The biggest indicator of a bad chip would be a value less than .2 (probably a short). "

This procedure is from: http://www.pinrepair.com/begin/

#12 9 years ago

^^^^ follow this advice. Less than a dollar per logic IC.

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