Problem: After my first attempt to fix the bloody Who Dunnit slot reels, the rightmost reel started acting up again recently - it spins freely, but stops after one or two turns max.
Solution: Checking into problem, i noticed that the slot index opto of the right slot reel wasnt registering. Time to have a look at the switch matrix.
As we can see, two wires (ORG/GRY, which is in reality WHT/GRY and GRN/YEL) are involved. Connecting the wires from the right index opto to the middle opto didnt change anything either, so that ruled out the opto board itself. Following the wires, a broken cable was discovered on the WHT/GRY wire at the BLACK target. Soldering the wire back to the target fixed the issue. Problem solved.