After an accidental short while working on the game, one row of switches still registers in switch test but doesn't work properly in play (for example, the lower holes don't award what they should and the ball is kicked out by ball search).
One switch row works in test but not in play: overheated strobe MOSFET Q36
Cause: The MOSFET that drives that switch strobe (Q36, strobe 3) had been damaged and was running very hot. A second burnt MOSFET, for a flasher, was found on the same board.
Checks
- With the game on for a short time, carefully feel the MOSFETs on the board for one that is much hotter than the rest.
- Look up which strobe the faulty switches share and which transistor drives it.
Fix
- Replace the damaged MOSFET (Q36 here), and check the others for damage from the same event.
Parts can be hot enough to burn; touch them only briefly, and work on the board with the game unplugged.
Systems
Games
Related tips
- Using the flippers scores points: a target switch closed by vibration
- Where the boards sit in a System 3 dot matrix backbox
- A whole row of eight switches dead
- Closing one switch shows several in the same column
- Proving the driver board's switch strobes
Source: Pinball Repair help group!! (Facebook group)