The diverter under the playfield (solenoid 38) stops working and its coil is found burnt; a new coil stays energized and gets hot, and the 3 A fuse for that circuit (F103) blows.
Underplayfield diverter coil burns and locks on: shorted Q15 on the aux 8-driver board
Cause: The coil's driver transistor, Q15 on the small auxiliary 8-driver board in the backbox, had shorted. Members say these boards are often damaged when a wire at the top drop target breaks and shorts, which the well-known tie-back modification prevents.
Checks
- The coil-to-transistor chart on the back of the backbox door confirms which transistor drives the coil.
- If a coil locks on as soon as the game powers up, test that transistor before fitting another new coil.
- Check the other transistors on the aux board too; several can short at once.
Fix
- Replace the shorted driver transistor (Q15 for coil 38) and the burnt coil, and replace the fuse.
- Do the tie-back modification at the top drop target wiring so a broken wire cannot damage the aux board again.
Systems
Games
Related tips
- Aux 8-driver boards must be jumpered for their game
- STNG: diverter coils lock on during play
- Solenoid numbers above 28 and the 8-driver auxiliary board
- STNG: under-playfield diverter coils lock on during play
- 20-second test for shorted coil driver transistors
- All flippers fire at power-up and blow the 50 V fuse: aux board ribbon upside down
- Solenoids 1, 9, 17 and 25 dead together: reseat the CPU to driver ribbon
- STTNG 8-driver board keeps misbehaving: the lower diverter coil was the cause
Source: Pinball Repair help group!! (Facebook group)