After power-up the first game plays normally, but trying to play another game freezes it; it sits happily in attract mode for hours and works again after a power cycle.

Locks up when a second game is started: bad 5101 RAM

Cause: The 5101 RAM on the MPU, used as working memory, had failed.

Checks

• Unplug the small reset board above the MPU to rule it out.
• In switch test, check each switch lights only one switch number.
• Look for the 5101: on many boards it is soldered in, but this one was socketed, so a swap was easy.

Fix

• Replace the 5101 RAM (socket it if it is soldered in).

Systems

• Gottlieb System 80A

Games

• Ice Fever

Related tips

• Boots into audit mode every power-up with good batteries: bad 5101 RAM
• Game powers up in audit mode instead of attract mode
• Game keeps resetting: replace the 5101 RAM (an NVRAM works)
• Game always powers up in audit mode: bad 5101 memory chip
• 5101 RAM at U8 fails often; speed matters
• Two flashes only: U8 5101 RAM
• Odd high scores usually mean a bad 5101 RAM
• System 6 won't boot and fails the 5101 RAM test even after replacing it: bad 5101 stock

Source: Pinball Repair help group!! (Facebook group)