*solved. It was a burnt trace near the battery after all.
Where to start?! I'm working on South Park for a friend, and he got it from someone that obviously robbed parts from it to fix another. I'll try to list everything I've done to it, and have videos to show what's happening currently when I try to fire it up.
I've replaced missing coils, switches etc with new matching parts, new ribbon cables, new DMD power supply, clipped and checked every diode on every coil under playfield, New Bridge rectifier on BRDG21 for 5volt, all connectors reset several times, connectors and pins in great shape (no burning), I re-flowed the solder on all the connectors, socketed chips removed and replaced (all in great shape), I buzzed out the legs of the chips around the batteries and all are connecting, Remote battery pack installed although no alkaline damage at all on board, New fuses throughout and clips in good shape.
The 5 volt seems to be unstable for some reason, or else both of my crappy dmm's are lying to me. It will stay at 5.1volts sometimes, then seems to drop below 4.5 and back up, over and over, then stable again. This was why I replaced BRDG21 in hopes that the 5 volt would stabilize. I tried measuring it on the MPU board as well and it was doing the same thing of course. I tried removing J16 and the 5 volt was still unstable on the driver board. I haven't tried testing my DMM's on the 5 volt circuit in another game yet but should probably do that.
The L200 light goes on and off on the MPU, sometimes stays on, sometimes stays off. I guess it suggests an issue with the MPU, but it could be the 5 volt issue, or ROM, RAM, CPU chips. The MPU is pretty much immaculate looking with no battery damage and no previous work done to it. The DMD does flash the initial screen from time to time but that's it, and I get a little blurb of the startup music every once in a while.
The driver board has had a few transistors replaced, and the bridge, but nothing else that I can see and the work looks well done. I got the old bridge off with ease by cutting the legs on the old one and heating them to pull them through, and it went very well. It didn't change the 5 volt stability at all though.
I have looked through every forum topic to try to figure this out, but I'm getting to a point where I really could use a little help. It would be much appreciated.
I didn't do anything different between the 4 videos below, just turned the machine off and restarted it. It does something different every time I start it lol.