well, as a follow up... the machine continued to exhibit unreliable behavior after the chip D100 treatment and resetting in the socket. 62-0 errors, slow reel movement, dead display, difficulty booting up requiring several power cycles. to that end, i ordered a set of RAM clear chips and a new SP611 game prom.
the reset chip arrived today, game prom on Monday. being impatient and against much advice, i did a RAM clear. symptoms don't fit with what a RAM clear is suppose to fix but i did it anyway. machine came up, one error, cleared easily, and is now operating faultlessly. so, i'm resetting my arbitrary 2 week clock of stability without an error starting today. if a get another 62-0 error, i'll replace the game prom right away but i'll hold off sticking it in until this existing one is proven bad.
the machine had sat for a long time with a dead battery before i got it. dunno if that can cause a multitude of errors that a RAM clear can fix.