The WPC clock gains only about 6 hours a day even with new batteries.

Game clock runs at a fraction of real time with new batteries

Cause: A battery fitted the wrong way round (the middle one especially) gives a low memory-protect voltage: settings survive but the clock stops at every power-off. Otherwise the clock circuit (ASIC U9, CMOS 4584 at U21 and the 32.768 kHz crystal X1) is at fault; one board had both crystal legs soldered to the same trace from the factory.

Checks

• Check all three batteries face the same way.
• Inspect crystal X1 and confirm its two legs go to separate pads.

Fix

• Refit the batteries correctly.
• Refit or replace the crystal so each leg is in its own pad; replace U21 (4584) if needed.

Systems

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

Related tips

• Settings are lost at power-off even with fresh batteries: bad battery diode D2
• What is on the WPC CPU board
• What the WPC custom chip does
• What fails on a WPC CPU board
• Running a WPC CPU board on the bench
• WPC CPU board versions and where they fit
• "Time and Date Not Set" message
• WPC-S and WPC-95 security PIC (G10) is game specific

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