Intermittent faults such as the game dropping to game over at random, wrong credit counts or features acting erratically.
Random game over, lost credits or erratic features
Cause: A missing, open or badly soldered coil diode letting voltage spikes into the logic, a poor ground, a loose PROM, a weak 12 V bridge or filter capacitor, a failing line filter, or +5 V set wrong.
Checks
- Confirm every coil has its diode, the diode solder joints are sound and the diode is not open.
- Check that the game is properly grounded.
- Press the PROM(s) firmly into their sockets.
- Check the 12 V DC bridge rectifier and its filter capacitor on the bottom board.
- Check the +5 V DC adjustment on the power supply.
Fix
- Repair the fault found; if nothing else is found, replace the line filter on the bottom board.
Line voltage is present at the bottom board, line filter and primary fuse whenever the game is plugged in.
Systems
Related tips
- Bookkeeping totals or score levels are wrong or missing
- Game check-out, part 2: what a healthy power-up looks like
- Scores light at once and the status display stays dark
- How the control board reset circuit works
- A coin chute switch does not register or registers wrongly
- A playfield switch triggers the wrong response
- Game Over (Q) and Tilt (T) relays are not fused
- The wrong sounds or tunes play
Source: System 80 Service Manual, Gottlieb