This Black Knight pinball had a problem that would not start a game even though all three balls were in the trough. I checked the switches, and all looked good. Put two balls in the top lock and tried to start a game, and still no luck. Put the game in switch test mode, and could tell that switch 17 (right trough) was not registering. Unplugged the connectors at 2J2 and 2J3. I used an alligator clip and tested 2J2 pin3 and 2J3 pin 1 and “17” showed up in the test. This made me realize that it’s not a board problem and then could focus on the playfield.
Checked the switch with my DMM and was showing that the switch was making good contact when closed. Looked at the switch matrix and started testing for continuity starting at the tilt bob to the right trough switch. There was none. Kept following from the tilt bob, and found a broken wire on the top drop target. Re-soldered the wire, and the game now starts!
This ended up being an easy fix, but happens quite a bit with pinball machines.