The left side general illumination is out while the right side works. The GI relay on that side clicks at power-up but does not respond in solenoid test, and it runs much hotter than the relay for the working side.
One side of the GI stays dark, GI relay held off: bad MOSFET on a replacement MPU
Cause: The MPU transistor that drives that GI relay had failed and was holding the relay in the wrong state. On the Rottendog replacement MPU the part is the MOSFET at Q30 (by R37); on an original Williams board the same job is done by Q17, and the two boards are laid out differently.
Checks
- Run solenoid test and check whether the GI relay for the dark side pulls in when selected.
- From the schematic, trace the relay's drive line back to the MPU and meter the transistor or MOSFET that switches it.
- If the game has a replacement MPU, use that board's own documentation to find the part, since the reference numbers differ from the original manual.
Fix
- Replace the failed drive transistor (Q30 on the Rottendog MPU, Q17 on an original board) and retest the relay in solenoid test.
Systems
Games
Related tips
- Backbox GI out, playfield GI fine: sticking relay on the backbox lamp board
- System 11 general illumination
Source: Pinball Repair help group!! (Facebook group)