Quoted from desertT1:
Does this require a logic probe, or can I do it with my DMM? I need a logic probe, just keep forgetting to order one.
Its best to use a logic probe or o-scope for stuff like this but a DMM can detect some problems.
You can do power off diode test. Red lead on ground and black lead touch those chip pins. You should see around 0.600v or so much like chekcing a diode. Reading of open or really low, below like 0.200 is a clue of a problem. Compare against a working board if you can.
You can also just check continuity with the DMM on beep test (game power off). Make sure the data, address, ground, +5v pins are all have continuity back to the cpu chip. CE1 CE2 and OD pins go back to where i mentioned above. the RW pin goes back to the CPU too.
Power on test you can check voltage at those pins. If you look at the MPU schematic Bally wrote in average VDC readings for certain places... im not sure about the ram chip enables, but about 2.5vdc reading on the chip enable pins would make sense.... again compare to a working board.
I think most likely is there is an open trace down by the ram chip and the CPU can't communicate with it. Could have a bad chip somewhere else tho like U18 or U17 but... less likely failure.
The imprint of the 5101 chip still looks funny to me. Can you double check that chip is OK in another board? All the ones i have ever seen with date codes past the mid/late 1980s have a white stripe on the far left side and the font is different. KFM vs MFM might be a different plant marking tho... can't say for sure.pasted_image (resized).png