I put a meter on the +5 at the power supp and with each time the flippers were pressed (at around 1 second between each press) the voltage would drop .03 of a volt (5v, 4.97, 4.94, 4.91 and so on) until the machine would reset.
Hmmmm, the accumulative decrease in volts looks like the main filter cap(s?) is dodgy and not recovering/charging quick enough to feed the regulation circuitry....
I haven't had the pleasure? of working on a dog board, so i'm not familiar with whats going on around their regulation design.....
just my 2cents ;-)
MM