PIA LED/Suspect Component/Location

Stays On/One of the 6821 PIAs/various
Flashes 1 Time/6064 RAM/ D5
Flashes 2 Times/EPROM /B5
Flashes 3 Times /EPROM /C5

From your information, it sounds to me like one flash, this chart says 6064 RAM would be a suspect. From other information I have found online, the suggestion is to install a test ROM for diagnosis.

Perhaps another Pinsider knows more or has experience with this problem, please stand by.

I had a similar issue recently with a MPU that I know was working 100% for years. It ended up being the batteries. Data East MPUs seem to have a hard time booting if the voltage being supplied by the batteries is between 1.5 and 2.5 volts. Can you test on the board to see how much voltage you have where the battery holder connects to the PCB? (It's to the right on the holder)

Also, you could remove the batteries completely and quickly flip the game ON-OFF-ON within 1 second to see if that gets it to boot. DE MPUs work just like System 11's... Just keep repeating it over and over in your head... DE MPUs work like System 11's, DE's work like System 11's.