The LEDs (or System 7 "0") flash once and then light steadily.
CPU LEDs flash once, then come back on and stay on
Cause: The CPU started but then stalled: bad ROMs or ROM sockets, or a failed PIA on either board.
Checks
- Run Leon's test EPROM, first without and then with the driver board.
Fix
- Replace the failed ROM, socket or PIA.
Systems
Related tips
- Add two test LEDs to a System 7 CPU board
- CPU LEDs (or System 7 digit) never light at power-up
- System 7 CPU LEDs are swapped versus System 6
- Late System 7 CPU boards lack LEDs and DIP switches
- Is it the CPU board or the driver board? Boot the CPU alone
- System 7 CPU jumpers differ for Hyperball, Defender and Star Light
- Re-jumper a System 7 CPU from Defender/Hyperball/Star Light to a standard game
- Identifying a System 3 to 7 CPU board
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)