I had some time yesterday to look more into the pcb troubles. When plugged in, the screen shows garbage letters and digits. The watchdog is barking at the 6502 as often as it can so the CPU is being constantly reset. There seems to be activity on all address and data lines, both on CPU side of things and on RAM/ROM side. I can't see any stuck pins on ram/roms. One is floating on one of the rams but it's not supposed to be connected to anything. I tried replacing the cpu but it did not help. I only used my logic probe yesterday but I guess I need to start scoping things out. I might also try to disable the watchdog just to see what happens. There's no watchdog disable signal on the schematics but I guess I could just tie the output to gnd (it's then inverted before reaching the cpu), or?
The roms seem to be mask roms. I don't have the board nearby atm and don't quite remember the model. Anyway, I bet my shitty eprom programmer won't be able to read them.
Rams are 2102a. I don't have any spares or otherwise I wouldve tried piggybacking.
The problem with the reset is present both when test mode is on and off so I guess it's related to something early on in the boot process. I'm not sure what roms are responsible for what.
I just had a look at he schematics and they’re very similar to other Atari games of this era. Take at look at the 3901’s at F2,D2 and E8, I’ve seen those all have a high failure rate, outputs usually stuck high or showing no signal, they control the Prom select lines & part of the reset circuit amongst others. These 3901’s all being faulty will contribute to the CPU watchdogging.
Also going from my previous repairs, if the RAM’s are made by NEC i’d also say there’s a high chance they will be faulty.
Reading the MAME source file Roms at D1 & E1 contain the CPU program.
EDIT, if you have the prom version of the board they are locations at L1,L0,M1,M0,N1,N0,P1,P0. This is very similar to a Super Breakout board in PCB layout and design.
Good luck with the repair.