After replacing the power driver board, I thought all was well, but unfortunately it wasn’t so. 😐 The machine would play normally most of the time, but then all of a sudden in the middle of a game it would go completely hay-wire and start triggering every functionality in the game simultaneously. Needless to say, the game would get extremely confused and eventually simply reboot.

At first I was worried I was still having power issues. And with a brand new power driver board! Very frustrating, especially since the problem was so intermittent. In the end the switch test mode proved invaluable in debugging the issue. As soon as the machine started acting up, I went into switch test mode, which revealed that all the opto switches were flipping between on and off at an extremely high rate of speed. After a few seconds, they would stop, at which point the game would play normally again.

An opto switch is a combination of an infra-red transmitter and receiver. The transmitter part is always on, and when some object (the ball, a drop target, etc) blocks the path of the light to the receiver, the machine can sense it. Since pretty much all the optos were firing at the same time, the problem seemed to be with something common to every opto that was mis-behaving. This lead me to suspecting the power connection that feeds all the opto transmitters. Looked it up in the STTNG manual, and found that the optos have a common power lead at J117 on the power driver board.

Sure enough, this connector looked really flaky! And better yet, if I fiddled with the connector with the machine in switch test mode, I could reproduce the opto insanity! It was pretty clear that this flaky connector was the source of the problems. There’s so much vibration in pinball machines that a flaky connector will work one second and not the next.

Some googling revealed these are .156-series molex connectors. A trip to my local Fry’s is all it took to get a replacement.

Here at J117 (bottom left of the power board) is my brand new connector. My wiring is spliced in to the original wires. The only reason I didn’t crimp the original wires directly into the new connector is that the original cables were quite short, and I didn’t want to risk running out of cable if I screwed up the crimp and had to start over. Hey, I’m new at this! That said, I can happily report that since my new connector went in, opto insanity is history!