The solenoid fuse blows as soon as the game is switched on, with no coil locking on. Unplugging the solenoid connector for solenoids 1-8 stops it, and several driver transistors appear shorted when buzzed in circuit.
Solenoid fuse blows at power-on: frayed 28 V wire touching ground under the playfield
Cause: On the circuit for solenoid 6 (the 'Flash' lamps), a few frayed strands of the 28 V supply wire were touching a ground wire at the solder terminals under the playfield. The lamps' driver transistor (Q25) was also shorted, locking those lamps on.
Checks
- Measure each coil and test each diode on the solenoids fed by that connector.
- Then check anything else on those drivers that is not a coil, such as the flash lamp circuit, for stray wire strands between the supply and ground at the solder lugs.
- Don't trust in-circuit buzz tests of the TIP120s: lift one and test it out of circuit before replacing them all.
Fix
- Separate and trim the frayed strands and insulate the joint.
- Replace the shorted driver transistor (a TIP120 at Q25 here).
Systems
Games
Related tips
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- Bring a repaired board set back into the game
- One or a few coils lock on at power-up
- Check the wire from the coil to its driver transistor
- A cracked coil diode keeps killing its driver transistor
- Nearly every coil energizes at power-on
Source: Pinball Repair help group!! (Facebook group)