After a few days of good play the game reports a trough error and puts two balls in the shooter lane. Removing one ball seemed to help.
Trough error and two balls served at once: faulty trough opto board
Cause: A faulty trough jam opto. With the two trough boards held together outside the game, every opto light went out except the jam one.
Checks
- Take both trough opto boards out and hold them face to face as in the trough: every receiver indicator should change together.
- Check the wires and pins between the trough boards and the node board.
Fix
- Replace the faulty trough opto board (here the receiver board; replacing only the transmitter board didn't help).
Systems
Games
Related tips
- Modern Stern trough kicks out two balls at once: check the trough opto boards
- Ball ends mid-play for no reason: trough opto connector pulled half out
Source: Pinball Repair help group!! (Facebook group)