I just got a Twilight Zone, and I'm having some occasional problems with ALL of the optos going out simultaneously (well... not the clock). During a game, everything will be working properly one minute and all of the optos will go out the next. This causes a lot of crazy things to happen, since the game all of a sudden thinks there are 3 balls locked, 1 in the VUK, 1 in the automatic shooter lane, and balls in the orbits and on the powerfield.

If I enter switch test while the game is malfunctioning, all of the opto switches are off. I've included a picture of the switch grid in working and non-working states. What's especially interesting is that as quickly as it breaks, it fixes itself and the switch grid returns to normal. I've tried wiggling connectors, banging on the machine, and pounding the flippers to fix the problem, but it typically just starts working again with no trigger while I'm not even touching the machine.

I reseated all relevant connectors in the backbox and on the opto board under the playfield. I measured 12V on the opto board during a failure, and the voltage looked good. I've not yet used a camera to see if the LEDs are transmitting, although I know that might be a good next step.

Does anyone have any guesses as to what my problem could be, how to fix it, or how to further diagnose it?

Thanks,
Tom

opto.png

I really don't think this is a mechanical vibration issue. The optos have recently gone out and come back on a couple minutes later while the machine has been sitting untouched. Additionally, banging on the flippers, shaking the machine, and wiggling all of the connectors has no influence on the optos when they are working or not working.

I've intended to follow maddog14's advice, as obvious as it is, but I haven't quite had the time to research it.

I looked at that board very closely, and all of the connectors looked nicely soldered. i also wiggled the connectors extensively, but that didn't make them change state (from working or non-working).

Thanks for the advise. I'll take another look at this board.

I'll have to pull the board and take a close look. I don't know anyone else with a Twilight Zone, so I don't think I'll be able to try swapping. At the moment, the problem is intermittent enough that it's still a minor problem.

Road Show doesn't have the board or nearly as many optos (if any), but that is a good guess.

Thanks for all the insight!

Great! Thank you for the tips, everyone!

This problem has been ongoing, but this week I discovered that new and improve replacements of the A-16807 opto board are available for around $80. I was thinking about ordering one, but figured I'd try to decisively conclude that the opto board was the problem first. The manual has a lot of info on the board, but not much of it is common to all 10 optos.

After snooping around, reflowing solder, measuring voltages, etc., I think my 12 V might be the problem. My machine is modded with color changing LED strips behind the door on the translight. The LED strips are powered via 12 V on the coin door interface board.

TP1 on the power driver board measured 13.7 V with the LED strips connected and 14.4 with them unplugged. I unplugged the LEDs and had my machine on for at least an hour and didn't see the optos act up.

Edit: discovered that the problem still occurred with the LED strips disconnected

I pulled my opto board and investigated very closely. The capacitor on that board (C1, 100 uF) clearly leaked and caused some corrosion. Some of the traces in that area looked suspect. I followed and tested a bunch of traces with a multimeter and found one from the capacitor to pin J5-2 (12 V from power driver board) that did not look good or test good. I installed a short jumper, reinstalled the board in the machine, and it has worked perfectly for several days.

I need to get a replacement 100 uF capacitor, of course. Until then, though, it seems that I have identified the cause of my problems.

Pretty sure I've fixed my problems. The 100 uF capacitor at C1 of the opto board leaked, caused some corrosion, and damaged some traces. I think damaged traces were more of a problem than the capacitor itself, but I replaced the cap and repaired the board, and I think I'm back in business.

It seems that 100 uF capacitors from 90s machines are starting to fail more and more now that they're 20+ years old.

See also: C2 on the power driver board of WPC games.

I almost used the term "preventative maintenance" in the last post. The corrosion from the leaked electrolyte doesn't cover a big area, but it is damaging.

I'm not going to do it personally, but preventative replacement of C2 on the power driver board also doesn't sound like a bad idea.