The 5 V output has a crowbar for overvoltage
CR8 (a 5.6 V zener) and SCR1 form an overvoltage crowbar on the +5 V output: if the 5 V climbs too high, the SCR fires and shorts the output to protect the logic chips. Setting the 5 V adjust pot too high can fire the crowbar.
Systems
Related tips
- 80/80A power supply has 12 V but no +5 V
- Check power supply outputs with the output cables unplugged
- Power supply output wrong
- Game does not power up properly
- How the 80/80A power supply makes its four voltages
- Both halves of the power supply limit their current
- 80/80A power supply test points and connector pins
- Typical voltages inside the 80/80A power supply
Source: System 80 Service Manual, Gottlieb