As said on RGP and in other posts, you need to check what's causing the opto switch problem.

Just as a test, I pulled the connector for the optos. I get your exact condition.

This issue could be as simple as the connector is unplugged; a broken wire; or perhaps the optos themselves are failing.

Optos always send the signal. If the signal is not being received (or the receiver has failed), the signal from the switch is gone.

faz

Williams compensates for switches that are out. I'm not sure how it would compensate for all buttons being out, but if one or two is out, it will allow the game to progress with only three of the switches working.

There's a key sequence to reset switch errors. If you press the credit button during Test 13, Test 14, Test 15 it resets all errors. I would guess if you did this, it would remove the instructions to compensate as well. It takes 30 games or 90 balls for the game to start compensating again.

Is that possible that you reset the errors??

faz

Excellent! Congrats!
faz