So I have been going through all the forum topics on this and wanted to document all my findings here. Most of the examples I have seen have L204 Blinking. If I disconnect the CN1 ribbon cable, L204 does blink on and off (as it should). Otherwise, L204 is always dead. The GI comes up, but nothing else. No boot sound, inserts, or DMD (ColorDMD lights up, but no data). All other LEDs are solid.
I do have one question. Where is the 5V test point on the CPU board? In the pinwiki it says "The +5V test point on the CPU / sound board is located just to the left of the 6809EP CPU chip (U209) on the board". I don't see any point like the 3.3V test point (a point with a square around it) for 5V and the manual shows no specific 5V test point.
I bought this game with an NVRAM already in the game. There was no corrosion anywhere when I bought the game and I don't see any now.
My CPU board is 520-5300-00 Rev. A and my Driver Board is 520-5137-00 Rev. G.
First thing I checked was the voltage at the bottom of R114 on the driver board and it has 5V. Voltages at CN2, TP1, VR1, VR2 and Pin 28 of U212 all check out fine. Pin 37 of U209 is High.
I re-seated all connectors, ribbon cables, the CPU, Game ROM and NVRAM. I even tried a different ribbon cable at J1 -> CN1. All fuses are fine.
I then traced the address lines (A0-A15) and data lines (D0-D7). I don't have continuity at the A14 connection of U209 (Pin 22) to U210 (Pin 29) and the A15 connection of U209 (Pin 23) to U210 (3).
Also for connections A16-A18 between U212 and U211, Pin 11 on U212 does not have continuity to Pins 6, 9 and 12 on U211, but Pin 11 on U212 does have continuity to Pin 3 on U211. I was going by the chart in the pinwiki.
This evening I did a brief attempt at following the schematics to trace the /BRESET signal back to the CPU board and test multiple things along the way. Only thing I noted down was that R271 on the driver board was 7.8k instead of 10k.
At this point I'm thinking at starting with re-socketing U209 and U210 based on the A14 and A15 results. If anyone has additional suggestions on what the problem could be based on these findings, I'm all ears.