Reset and clock are good, but with Leon's EPROM fitted the LEDs do not flash once a second.
Leon's test EPROM fitted but the LEDs do not start flashing
Cause: Usually one of: bad 6802/6808 at IC1 or its socket, bad IC17 EPROM or socket (or any socket), bad PIA at IC18, a badly failed 5101 at IC19, bad IC11 (74LS10) or IC12 (7408) in chip select, a broken address or data trace, or bad buffers IC9/IC10 (pre-System 6A).
Checks
- Remove the 5101 at IC19 and the static RAMs at IC13/IC16; Leon's code runs without them, and a shorted one can stop the board.
- Try a known-good CPU chip at IC1.
- Check address and data continuity from IC1 to IC17, the RAMs and the PIAs.
Fix
- Replace the failed chip or socket, or repair the trace.
Systems
Related tips
- Keep spare 6800, 6821 and 5101 chips
- Test the CPU board PIA IC18 with Leon's code
- Game always powers up in audit mode: bad 5101 memory chip
- System 6 won't boot and fails the 5101 RAM test even after replacing it: bad 5101 stock
- Boots into audit mode every power-up with good batteries: bad 5101 RAM
- Test the switch PIA IC11 with the Leon test EPROM
- Game keeps resetting: replace the 5101 RAM (an NVRAM works)
- CPU locks up as soon as the driver board is connected
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)