The auto-launch barely pushes the ball out of the shooter lane, in test and in play, yet it fires at full strength when its driver transistor's tab is grounded by hand. Coil voltage and resistance are normal.
Auto-launch fires weakly but full power when the transistor is grounded
Cause: A fault in the drive circuit on the power driver board ahead of the transistor, so the transistor is not being turned fully on. Grounding the tab bypasses that part of the circuit.
Checks
- Confirm the coil, wiring, sleeve and the small high-current driver board under the playfield are good.
- Swap in a known good power driver board; if the launch becomes strong, the fault is on the original board.
Fix
- Repair the drive circuit on the power driver board (pre-driver transistor, resistors, the driving chip or a bad joint) or replace the board.
Systems
Games
Related tips
- Supercharger diverter dead even in test: open TIP102 at Q81 that tested good
- 20-second test for shorted coil driver transistors
- No coils, lamps, GI or flashers but display and sound work: check blanking
- Testing a coil diode on the driver board
- Taking the power driver board out of the backbox
- WPC driver board: lamps, GI and coils all dead, CPU fine: broken blanking trace
- Learn the power driver board layout first
- Firing a coil by grounding its TIP102 tab
Source: Pinball Repair help group!! (Facebook group)