Modern Stern trough kicks out two balls at once: check the trough opto boards
When a modern Stern trough sends two balls into the shooter lane with a single kick (and the ball count is right), or the game sometimes ends a ball that hasn't drained, the usual cause is the trough opto boards misreading. Reseat, and if needed repin, the small connectors on the trough opto boards near the eject coil, and inspect the boards' header pins for cracked solder joints and reflow them. If that doesn't cure it, a faulty opto board (often the one nearest the coin door) may need replacing. On games with magnets, magnetised balls can also confuse the trough.
Systems
Related tips
- Trough error and two balls served at once: faulty trough opto board
- Ball ends mid-play for no reason: trough opto connector pulled half out
Source: Pinball Repair help group!! (Facebook group)