(Topic ID: 197531)

DMD flaky- world cup soccer


By JoshinDC

2 years ago



Topic Stats

  • 11 posts
  • 2 Pinsiders participating
  • Latest reply 2 years ago by ChrisHibler
  • Topic is favorited by 1 Pinsider

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#1 2 years ago

My WCS has an intermittent problem with the DMD display. Basically, when there's a fast animation, the display shows the wrong frame some of the time. One simple demonstration is to open the coin door: there should be a "coin door open high voltage disabled" type message, that flashes positive and negative a few times (ie, amber text on black background, then black text on amber). Usually (say 3 out of 4 attempts), instead the display will flash one of these "frames" (positive or negative), along with whatever had been on the screen before or recently (say, "game over"). This also occurs during the game enough that it's difficult to see what random awards are being given often times.

I re-seated and then replaced all 4 ribbon cables with no improvement. I've tested the voltages at the DMD driver board and they all check out within the ranges on pinwiki. I poked around a little bit on the board where I could test easily (for example, BR1) and everything tested ok (though I could have easily missed something)

I swapped my WCS DMD into my other game (no good gofers) and it worked fine, so I don't think it's anything wrong with the DMD.

The HV portion of the DMD controller board looks pretty crispy, but it also has definitely been repaired at one time. For example, the big electrolytic capacitors are 220 um, which is what gpe sells in their repair kits, but not what shipped with the game. I don't know if the components on it now have gotten hot or not. The big cement resistors are spaced off of the board a bit, which makes me think the burn marks are old.

I was planning on rebuilding the HV portion of the board, but I wanted to see if anyone had any insight beforehand. I've done some circuit board repair before, but not a ton, and the fact that the board has been rebuilt already made me 1) think it might not be the HV section, and 2) reconsider if I'm up for the task.

A side question: I assume that if I screw something up and can't fix it, I can still buy a piggy-back board to fix the DMD Controller and at the very least get back to where I am now. Assuming I don't mess with anything in the top 3/4 of the board, is that a fair assumption?

Thanks in advance,
Josh

#2 2 years ago

Hi Josh.

Put down the iron and step away from the machine...
The problem you are seeing is not power related. Rebuilding the power circuits won't help.

First, run display test all the way until the end. At the end of the test, the game should display "RAM TEST OK". If that does not occur, the game will flag a page error of some sort. Generally, this means that the RAM on the dot controller has failed. Aside from the HV circuits, the RAM is the most failure prone part on the board.

If display test passes, next up is the "paging" circuitry on the board. I'd ferret out the likely chips via schematic analysis. This is sometimes tough as the function isn't all that clear. You can also "diode check" every IC on the board, comparing odd results to a known good board. That takes some time, but it's generally a successful procedure.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#3 2 years ago

Glad I asked!

The display test ends with "RAM OK"

Any suggestions to where to start? I don't have another board to compare to unfortunately (NGG is WPC-95)

Thanks for all your help!
Josh

#4 2 years ago
Quoted from ChrisHibler:

Hi Josh.
If display test passes, next up is the "paging" circuitry on the board. I'd ferret out the likely chips via schematic analysis. This is sometimes tough as the function isn't all that clear. You can also "diode check" every IC on the board, comparing odd results to a known good board. That takes some time, but it's generally a successful procedure.

OK, I went through and started diode checking the ICs related to paging with my DMM, and the one "hit" I got was pin 15 of U32/pin 5 of U34, labeled "DISP_A3" on the diagram. This connection appears to be shorted (.02 V to ground on the diode check). I don't have a board to check this against, but it seems to be wired similar to pins 2, 7, and 10 from chip U32, which all read something like 0.5 V

This is the diagram I used: http://arcarc.xmission.com/Pinball/PDF%20Pinball%20Misc/Williams%20WPC%20DMD%20Schematics%2016-9473.pdf
The area of interest is in the lower left of the 9th page of the pdf, (labeled page 7).

Any idea how to tell which chip is causing the short? U32's output is connected to U34's input, if that makes a difference. U34 is close to the crispy area of the board, although it doesn't look like it's been damaged.

I assume my next step is to desolder the chip(s), install machine pin headers and snap a replacement chip in. I'll order both chips and just try one at a time if I can't figure out the culprit without desoldering.

Is there anything else I'm missing? Anything else I should add to my mouser order?

Thanks in advance (and thank you chrishibler for stopping me from fixing what wasn't broken),
Josh

#5 2 years ago

I'll test one of more of mine tonight so you can compare.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

#6 2 years ago
Quoted from ChrisHibler:

I'll test one of more of mine tonight so you can compare.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

Thanks, that'd be awesome!
Josh

#7 2 years ago

Sorry for the delay.
I get a normal diode reading of .678 on U32/15.
It's a good bet that you've found the culprit.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

#8 2 years ago
Quoted from ChrisHibler:

Sorry for the delay.
I get a normal diode reading of .678 on U32/15.
It's a good bet that you've found the culprit.

Thanks so much! Any idea how to tell which chip is bad without soldering? Any educated guesses which it is? I'll just buy both, but I'd love to desolder/solder 1 chip instead of 2.

Thanks again,
Josh

#9 2 years ago

I have seen where the tech, would clip the leg near the PCB. That would allow isolation of the particular chip. And it's relatively easy to resolder where the leg was clipped. I've never done it. I prefer to simply desolder.
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

#10 2 years ago

Well, it seems to have worked! I removed U32, installed a machined pin socket and a new chip, and no more flakiness. Thanks so much chrishibler for your help! I owe you a drink if we ever meet.

Josh

#11 2 years ago

I'll hold you to that!
--
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

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