Looking for some help here. I’m working on a Gottlieb Monte Carlo and I’m having problems with the MPU board. Before me there were a few things done to the board, a couple of resistors replaced, Q2-Q4 replaced, the first 2 sets of dip switches have been replaced. The piggyback board has been replaced with a Swemmer board. When I first got it the only thing that would happen when you turned on the power were some GI lights and for some reason the left flipper was working.
Since then I have recapped the AUX power supply, new trim pot on the PS along with new connectors. I did the ground mods in the cabinet along with the mods to the boards and the A1J4 connector. The game roms were bad as well and have been replaced.
I took the board out to bench test with Marcos test rom and I got 1 flash. Seemed to be the 5101 chip, I had a NVRAM all ready on its way. I put it in and the test ran fine, even the extended test. I put it back in the machine and it was working. Now the downward spiral begins. I stated to notice strange high score come across with odd characters for names, they were still the preprogrammed high scores. I then looked at book keeping and would see like 880 replays, 88 coins and so on a lot of “8”s when it should be a “0”. Then the memory check said the 5101 was bad. With how everything above was acting I thought so too. Then I started to have the MPU lock up, the scores would freeze and I would have to turn the machine off and on. It would boot up for a few seconds then lock up again. I even had the wheel spin and some sounds play from time to time. So back out to test. Macros Rom is back to 1 flash I ordered another NVRAM and still 1 flash. I tried Leons test rom also and I’m getting the same 1 flash. When the test chip is in I’m getting pulsing address and data lines. The U1 pin 40 starts low then goes high. The clock is pulsing at U1-37 and 25, all Riot chips are receiving the clock pulse as well. I have checked most if not all of the other logic chips and all of the logic appears to be correct, some I’m not sure the input is right but the output is right for the type of gate. I have checked continuity between the lines going between U1-U6. I checked to make sure the legs wean't some how shorted to ground or the voltage. The only thing I can think of that could be is either the delay or memory protect circuit since they feed the 5101 ce1/ce2 but I’m not sure what to look for at this point. I want to add in case it might help if I connect the reset board even when it was working it would constantly reset the mpu, it seemed to be a time pulse not random resets.
So if you read all of this and I didn’t loose you and have any have any ideas whats going on please post. I know I am missing something here just not sure what.
Thanks in advance.