The CPU board would not boot. Unloaded, the power supply's 5V read normal, but it dropped away as soon as the CPU board was connected, and the 12V and -12V readings were also wrong.
CPU won't boot, 5V collapses under load: replaced bridge not joined on the top side
Cause: An earlier repair had replaced the bridge rectifier, but its positive lead was only soldered on the underside, and the connection to the filter capacitor (C4) runs on the top side of the board, so the regulator got no proper filtered DC.
Checks
- Look closely at earlier repair work on the power supply: replaced bridges, caps and regulators.
- With the game off, check continuity from the bridge's + lead to the + of the main filter capacitor.
- Also check the small filter caps near the regulator; failing ones cause similar 5V faults.
Fix
- Solder the bridge lead on the top side as well (or add a short jumper) so it joins the capacitor trace, then recheck the voltages under load.
The power supply carries transformer AC and the high-voltage supplies; unplug the game before working on it and let the capacitors discharge.
Systems
Games
Related tips
- Alphanumeric games need the 520-5000-00 supply
- Adding jumper wires across DB1 and C4 (520-5047-00/-01/-02)
- Power supply board versions are not interchangeable
- Z1 on the power supply is a varistor, not a diac
- Power supply board versions and their +5 V filter capacitors
- Power supply CN1 pinout, pins 1-6
- Power supply CN1 pinout, pins 7-12
- Power supply gives no +5 V
Source: Pinball Repair help group!! (Facebook group)