Verified balls were continuously firing. Removed balls and used switch edges test to verify that trough switches 1-6 were good. However, switch 87, “top trough” was not working.

Dismounting the LED panel, I verified that all the LEDs were working except LED1 (see photo 1). I checked the voltages and they seemed fine. Assuming that it was a bad LED, I replaced it. That didn’t fix anything.

Putting it back, I again checked voltages and got inconsistent readings on this LED. The cause turned out to be a broken resistor wire (photo 2). When pushed down it worked, explaining the intermittent readings.

I resoldered it. I ended up with a firm connection and a working LED (photo 3). I will order more resistors so we can replace this and the lower-wattage ones on the board.