(Topic ID: 312746)

Everything works except for GI after replacing CPU Board

By JoeChamp

2 years ago



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#1 2 years ago

Just bought a new CPU with NVRAM from Marco Specialties. Properly removed chips from old damaged board and inserted them into new board. Installed board to machine and plugged everything in. Strangely, everything works except for the GI lights. Game plays fine, all inserts light up, flashers light up, but no GI on playfield or backbox. However when I short two of the three legs of the any of the transistors on the GI circuits with the point of my multi meter probe the GI lights illuminate on the playfield and backbox accordingly. What do you think I should check?

BTW, this was a working game prior to installing the new CPU board. Full disclosure... I tried to replace the RAM with a new socket and NVRAM and lifted some traces. I worked to repair them and thinking they were good I installed the board and fired up the machine. It wouldn't boot up. That's when I ordered a new CPU from Marco. While installing the new CPU board, I found two fuses were blown one at f112 and one at f601. I replaced them with the correct fuses. All fuses on all boards were removed and tested then reinstalled.

Please help point me to the right thing to test or fix? I'm waiting for the new CPU board manufacturer to call me to discuss if the issue is with that board or not. I did notice that the LED at d19 does NOT come on at all when switching the machine on. d20 blinks and d21 is solid on.

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#3 2 years ago

I tested j115 and found there to be 7.86 volts between all pin 8 and pin 3. In fact I checked every pair and got the same voltage reading.

Would this have something to do with U1?

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#4 2 years ago

Sounds like a ground problem. Did you double check the ribbon cable from the CPU board to Pwr Drvr Board? And all the grounds

#5 2 years ago

I pulled this ribbon cable off and triple checked connection. I even turned it around as pictured thinking it might connect better this way.

If I take my mm set to 6v and touch leg 3 and leg 10 of the chip at U1 all the GI lights come on.

It looks like everything should be working. I'm losing my mind here.

After pwering off andcremoving the ASIC chip, I did a continuity test between pin 66 of the ASIC socket and leg 1 of U1 and found there to be continuity.

What else should I do? BTW I don't have a logic tester.

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#6 2 years ago

Pin 3 is D0 from the MPU.
Pin 11 (not pin 10) is the clocking signal from the ASIC.
Why the behavior changes when you measure between those I can not say other than the logic level of the pins is being changed.

I would say that you have a big coincidence here.
For whatever reason, the driver board picked this moment to fail. Most of the time, the issue is the the LS374, but removing that IC cleanly is not trivial.

As always, "divide and conquer" is a good strategy.
Swap this driver board with the driver board in one of your other games.
See if the problem follows.

BTW--This is NOT a ground problem.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

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