After about an hour the displays drop digits until blank, coils only buzz faintly and background sound stops, though the game still coins up.
Displays lose digits and coils buzz once the game warms up
Cause: The blanking signal pulsing rapidly instead of staying steady (the blanking LED looks lit but is flickering). The faulty part was C58, the 1 uF electrolytic in the blanking circuit; the 555 and 2N4403 were not the fault.
Checks
- Watch the blanking line with a logic probe while warm.
- As a test only, tying U55 pin 1 to +5 V made the game run.
Fix
- Replace C58 (1 uF electrolytic), then the 555 and 2N4403 if the fault remains.
Systems
Related tips
- Resets continue after diode repair: power and connector checks
- MPU won't boot even though a test ROM passes every PIA and RAM: bad game ROMs
- Game will not boot consistently: power-on reset (POR) circuit
- Four beeps at power-up, GI only and no display: game has no batteries
- "Adjust Failure" at power-on
- "IRQ Failure" at power-on
- Won't boot even with a new CPU board and new chips: the new ROMs were bad
- Displays flash bright and speakers noisy, game does nothing
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell