On a replacement power driver board the LED for the unregulated 12 V (LED 103) stays dark and TP1 shows no voltage, yet fuses are good and the game seems to play.
12 V unregulated LED out on the driver board: open track to C8
Cause: The fine track from TP1 back to capacitor C8 was not connected where it meets one leg of C8: the plated-through hole was not joining the top and bottom of the board.
Checks
- With the board out, check continuity from TP1 to the C8 leg it should reach, on both sides of the board.
Fix
- Repair the open hole by soldering a few wire strands through it so the top track, bottom track and capacitor leg are joined.
Systems
Games
Related tips
- Shorted or open bridge rectifiers
- WPC-95: all the 20 V coils dead, fuse good
- Check fuses F106/F101 with no lamps and no game start: shorted bridge diode
- WPC-95 driver board LEDs and test points
- Supplies made on the WPC power driver board
- Choosing a replacement driver board filter capacitor
- WPC-95: a dark +20 V LED at TP104 means the flasher supply is not leaving the board
- WPC-95 LED102, LED103, LED104 or LED105 off
Source: Pinball Repair help group!! (Facebook group)