Ok, I'm not used to Zac machines yet, and I don't have the gear I used to for testing a non-booting board like this.
Basically, I'm suffering from a Devil Riders that won't boot. If I power it up, it constantly flashes zeros on the displays about every second. Reset line appears to be pulsing at about the same rate. Connecting CN11 pin 8 to 5v can get the reset line to a steady 0.6v, but doing a manual reset doesn't cure anything..... just shuts the displays off completely.
Doesn't respond to a Leon test ROM at all either. Either factory rom or Leon's gives me a steady LED on the MPU board. Doesn't currently have a battery installed, the good news however is there doesn't appear to be any battery corrosion either.
Somebody already went through most of the reset circuit, so looks like this problem has been going on for a while. Nothing I've poked at so far seems to individually be working wrong. But something is causing the reset circuit to keep firing.