The backbox running lights stay dark or stuck.
Backbox chase lights not running
Cause: A failed 555 timer, a dead chip in the counting chain, or failed MPS-U45 lamp transistors.
Checks
- With a logic probe, confirm 555 pin 3 is pulsing.
- Follow the schematic from there to find the first chip whose output stops pulsing.
- Probe the 10-pin connector, where all the MPS-U45 outputs land; a pin that does not pulse may be a bad transistor.
- Check the MPS-U45s on diode test.
Fix
- Replace the failed timer, chip or transistor.
Systems
Games
Related tips
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Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part Two, Clay Harrell (pinrepair.com)