Client called for repair on Junkyard, no boot situation. Checked voltages on driver board, and find that 5V is missing (no LED 101, only 1.4V DC at TP101.
I check the incoming A/C voltage at J129 and find 9.63V A/C, so I'm satisfied that it's a board level issue. I replace the voltage regulator LM317 at Q1 after checking the resistance of R1 and get 749Ohms, and R1 and get 242.6 Ohms. Figure that's close enough to ensure that we're getting at least real close to 5V from the Regulator. No dice, still no LED, and nothing higher than 1.4 at TP 101. I check and replace (even though they were OK) D7 through D10 with new components. Still no change. The only thing left is c9, and while I will replace that, when I get the part in, I can't see what's left if this doesn't solve the problem. Is there something I'm missing here? What else is left? Oh, I forgot to mention, I checked fuse F105, it's fine, continuity along the circuit is fine. I reflowed ALL the associated header pins with new solder, including the fuse holder legs, J 129, J 136 and 137, and obviously all the new components.

Any suggestions on where to turn next would be greatly appreciated, as I don't expect this will turn out to be a bad cap. P.S. this board was tested in a known working WPC-95 game, and the results are exactly the same, so it is definitely a driver board issue as far as I understand it.

Thanks

Ok, so I went back over the board and schematics one more time to check and see what I may have missed. Turns out, I replaced the wrong voltage regulator.... My eyes are not what they used to be, and I ended up replacing the VR at Q2 instead of Q1. In doing so, I realized that I replaced the VR at Q2 with the same part used in Q1, (although one is a TO type package, and the other is a TIP type package) So I order up a new LM 317 in a TO style package and replace that, replace the incorrect Q2 with the original LM 7812, and lo and behold, I have 5 volts back and the game boots...

However, I realize not all is good yet. I have absolutely ZERO playfield power. No GI lights, no CPU controlled lamps, no solenoid power, nothing!. Game plays blind, switches all register, backbox GI works fine, display and sound are fine, and all voltages check out on the driver board etc. CPU has obviously booted as the game is running, but the cabinet is absolutely lifeless.

Considering I did plug in the board with the wrong voltage regulator at Q2 one time, have I fried my CPU with the wrong voltage going through the 12 volt rail? That diagram I have does say it goes to the lamp matrix, but why no GI or solenoids, flippers, etc.?

I put back in the original (good) board, and the issues remain, so it's definitely something in the game at this point. (IE, not a missing or misplaced connector)

Let me know what you guys think.

If it is the CPU, where do I start to diagnose what took a hit?

Had already tried several times to reseat the CPU/Driver board ribbon cable thinking the same thing. Seeing the same results with both the original Driver board and the one I was working on repairing, I figured that wasn't the issue.

Went back up and tried again today (still didn't see that it was off a row etc.) It fired right up, everything is working as it should be. May have a flaky ribbon, or cold solder joint. If issues re-appear, I'll be sure to order a new one, and reflow the pins.

Thanks for the 2nd set of eyes on this one and the suggestion to try again. I thought I was in for buying a new replacement CPU.