Firing the ball launch (plunger) coil in solenoid test locks it on for a few seconds, then its drive transistor and fuse blow. With the coil unsoldered and a new transistor fitted, every other coil on that group works.
Launch coil locks on and blows its transistor and fuse every time it is tested
Cause: In this case the fault was traced to the game's transformer; the poster had already replaced every driver-board part in that circuit twice without curing it.
Checks
- Measure the coil resistance and compare it with the manual; a coil only slightly low can still cause this.
- Replace both the drive transistor and its pre-driver together after any lock-on.
- Remember that WPC games keep the coil diodes on the driver board, so this coil should have no diode of its own; remove one if it has been fitted backwards.
- Check the transformer outputs and windings for a fault.
Fix
- Replace the faulty transformer, along with the failed transistor, pre-driver and fuse.
The transformer primary carries line voltage; unplug the game before working on it.
Systems
Games
Related tips
- Several solenoids and a lamp group dead: reseat the CPU-to-driver ribbon
- Driver transistor dies after fitting a coil that has a diode
- Firing each coil from the WPC solenoid test
- A coil does nothing although its fuse is good
- WPC solenoid driver groups
- The four groups of WPC coil outputs
- One coil does nothing in the solenoid test
- A coil stays energized
Source: Pinball Repair help group!! (Facebook group)