There's a lot to unpack here. One thing at a time...
Quoted from drsfmd:If there are credits on the credit unit when the game is turned on (note: not pushing the start button-- as soon as the game is connected to power), the game lights up and immediately begins to decrement the credit unit. It continues to try to do this even after the credit unit has reached zero.
This sounds like two problems:
Cue Tease Replay reset (resized).jpg
First the Credit or Replay unit should stop resetting once it reaches zero credits. Check that the zero credits switch opens once the Replay unit reaches zero and that it's not somehow shorted by bent solder tabs or whatever.
Next it sounds like either the Start Trip relay or 2nd Coin relay is stuck on, or one of the switches shown above on those relays is stuck closed. I think these two should stay on for a score motor cycle and then relax once the game starts resetting. If the Start Trip relay is stuck on, check if the 25 Cent relay is stuck on too.
Beware that the Start Trip, 2nd Coin and 25 Cent relays are all in the 120 volt part of the circuit so observe them carefully and don't touch anything unless the game is unplugged.
/Mark