During play the left popper (mode start hole) fires by itself with its sound and flasher, and the right pop bumper fires at the same moment. New opto transmitter and receiver, a new capacitor on the opto board and a swapped opto board made no difference.
Left popper fires at random with the right pop bumper: shorted J127 header pins
Cause: Two header pins on the power driver board, J127 pins 6 and 7, had been shorted together by earlier poor transistor repair work. One drives the left popper and the other the right pop bumper, so firing either fired both.
Checks
- Note which coils fire together, then find their driver pins on the schematic.
- Inspect the back of the driver board at those header pins for solder bridges and damaged pads, and check for continuity between neighbouring pins.
Fix
- Remove the solder bridge or short between the pins and repair any damaged traces.
Systems
Games
Related tips
- A diode-mode transistor test is right about 98% of the time
- 20-second check for shorted TIP102s
- 20-second test for shorted coil driver transistors
- How a WPC coil, flasher or lamp driver chain works
- A coil or flasher energizes as soon as the game is turned on
- Learn the power driver board layout first
- Where the WPC coil and lamp drivers sit
- WPC power driver board versions and where they fit
Source: Pinball Repair help group!! (Facebook group)