The CPU batteries get hot enough to melt their wrappers.

Batteries get hot with the game on

Cause: The board is charging them, usually because diode D2 (1N4148) has failed.

Checks

• Test D2.

Fix

• Remove the batteries straight away and replace D2.

Hot batteries can leak or burst; turn the game off and remove them carefully.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Changing the CPU batteries without losing settings
• Cleaning up alkaline battery leakage on a CPU board
• Fitting a remote battery holder to a WPC CPU board
• New batteries but still losing settings: test the holder
• Battery power not reaching the RAM: diode D2
• Switch matrix row fails with good switches and diodes: battery-damaged CPU board
• New batteries die in weeks or settings still lost: U8 RAM
• Coin door Begin Test button does nothing: acid-broken trace on the CPU board

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Three, Clay Harrell (pinrepair.com)