I acquired my first pin ( Bram Stoker's Dracula ) in July but have had a series of issues that I've slowly been trying to track down and fix, learning as I go. At this point I seem to only have one real problem left, which is a problem I had soon after getting the machine, but its progressively getting worse. There's a lot of history but I'll try to only mention what's relevant:
1) I took possession of the machine, and within a couple of weeks I started having an issue where none of the high voltage coils would fire. Working with the seller, we assumed that the newly replaced MPU was to blame (he made mention that something similar happened to him but he thought he had resolved it with a MPU replacement). I got yet another new MPU board, swapped my ASIC/ROM/CPU and everything worked again. Important to note - this symptom was no ground going to anything on J-130 / SOL1-8 not firing.
2) 1-2 weeks go by and I start having issues again, but now fuse F105 keeps blowing. At this point I thought I had a new/unrelated issue and that I had a short on a drive wire for one of the high voltage coils.
3) After a lot of troubleshooting, I found Q76 was shorted and forcing J130-5 to ground (I assume the PDB became damaged from the original issue repeatedly happening & many F105 fuses blowing). Removing the PDB and testing this transistor proved to be bad. I ordered a new PDB (probably extreme, but I really want this fixed and my soldering skills suck).
4) I put the new PDB in and now we're back to the total inverse of 1; every pinout on J130 is grounded / all SOL1-8 coils perma-lock on startup and blow F105. If I remove the MPU > PDB ribbon cable and restart the system, J130 doesn't perma-ground. To me this points to an upstream logic issue, especially since the PDB is new.
5) I ordered a new 68B09E / CPU chip with my PDB because it was cheap and one of the last few pieces remaining to swap/test. So I remove the MPU and swap only the CPU chip, the new CPU chip is DOA and the system won't boot at all. I put the original CPU back in and the system boots fine and the J130 ground issue is mysteriously gone / everything works exactly like it should now. This was last night and I've played ~10 games with no issues, but I have no confidence at this point the issue will not return.
At this point I've replaced the MPU, the PWD, all ribbon cables & I'm relatively confident there's no short on the coils/wires. When I replaced the MPU originally, I have a feeling there was nothing wrong with the first MPU and just simply monkeying around with moving the ASIC/CPU/ROM was enough to "fix" the problem, just like how most recently just reseating the CPU seems to have resolved it. To add to this, it seems that the seller temporarily resolved the issue by swapping MPU's too, when it in reality it could have just simply been reseating/moving the ASIC/CPU/ROM.
By all logic at this point, it seems like the CPU is the culprit... but has anyone ever heard of SOL1-8 locking on or not firing at all as being symptoms of a bad CPU chip (or ASIC/ROM for that matter)? I'm going to order another replacement CPU, but I'm sort of at a loss here if/when it happens again if that CPU doesn't fix it. I did recently get a logic probe but am not 100% sure how to use it to troubleshoot this. Any advice on that would be awesome too?