Last night I did a quick test of going from VBATT to VRTC on the 0120 with my multimeter on mA with an 18650 providing power to the circuit through the battery connector because I was being a bit lazy. About 30mA still. So it certainly seems that the CUDA is drawing that current. But it also seems to be working so it seems even more likely that something on one of it's outputs is drawing more current.
I also made a second discovery. One of the springy ground things under the board had been bent and looked like it had been contacting a via near the ROM because the solder mask was worn off and the via was shiny. I really hope this was something that happened while I was testing the board. To be safe I re-bent it a bit more and put some kapton tape over the potential contact point. Plugged into the computer it doesn't even come close to making contact, so I don't know.
After my pointless testing I plugged the "bare" board in, added power and turned it on using the keyboard. It turned on and stayed on. Not much else happened obviously because there wasn't even the ROM or RAM in it. So I tried adding the ROM and RAM and it would only "bump" on for a couple of seconds and turn off again. Removed the RAM and ROM and this was still the case. Kind of gave up, put everything back in and back on and tried a power up again just in case. Still the same. It's been put aside for now.
Last night I ordered the SMD caps for it and the MOSFET that I'm slightly suspicious of. I also ordered caps for the 7300/200 motherboard, CPU board, and hopefully the needed parts for it's PSU.
I really need my scope. I feel like I'm working blind.