Do all the trough switches and the outhole switch under the apron show up when activated in switch test? Make sure to activate the switches with a ball. Before starting the switch test, make sure all drop targets are up. If the switches under the apron all check out, test all the switches in the upper lock trough with a ball and make sure they all register too.

Have you replaced the 40-pin connector between the driver board and mpu? Any other work you've done on the game?

Right on. Let us know how you fare this weekend, with any luck maybe it's just a switch out of adjustment or something relatively simple. Good luck!

I have the same problem with my BK. The sound works fine when hitting the test button on the sound board. I can see the signals being (attempting to be) triggered by the CPU board on the soundboard connection j3. I have used a logic probe and some testing to validate that the signals go low at j3 as expected or at least, they aren't stuck high or low. Disconnecting j3 on the sound board and grounding out one pin at a time has no effect either, but IT SHOULD trigger sounds. I have gone through the PIA, CPU, ROM/RAM and DAC and there is no apparent problems or stuck pins on those. The 4050 buffer chip has been replaced as I had that available for replacement. It seems like there is something on the input circuit to the board that is blocking the triggering of sounds. Anyone out there have this problem and know a fix?

With nothing connected to the inputs of the sound card, measure pin 3 of IC6 or pin 4 of IC7 (electrically the same). If this is LOW, check IC7 for a bad inverter. With nothing connected to the sound board inputs, all inputs of IC6 should be hi (2, 3, 4, 5, 9, 10, 11, 12). If all inputs are HI without sound board input, continue.

Put the game in sound test from the coin door diagnostics switches. This will cycle the sound board inputs through some of the sounds (grounding some sound board inputs). Put your logic probe on PIA pin 13. This pin should be going low and high as each input is triggered. Alternately, you can measure it as you ground and unground one of the sound board inputs.

If pin 13 DOES NOT go hi and low, replace IC6.

If it DOES go hi and low, replace the PIA.

Kick ass! I've had Black Knight for a few years and it's a lot of fun to play. Every now and then I run into the ball issue and it's always been just a little cleaning with the q-tip and rubbing alcohol on the trough switches and were back to playing again.