I've seen optos on Sterns have one of the solder pads break off the back of it causing intermittent connection. Also more rarely I've seen the lead inside the led actually break, also causing intermittent issues.

Old thread bump.

I just rebuilt a ST Stern after stripping it down to the playfield. It did exactly this. All 8 opto switches (ramps and vengeance) going spazzzztic. They are not on the same row or column, and span 4 different opto amplifier boards. I'll take a look at the back box, but it would appear that the ONLY way this could happen is intermittent +5V or ground that is common to all of those opto boards. I'll have to check J6 later.

wxforecaster Did you ever find out if this was the case of not? I have this exact thing happening?

wxforecaster and Ecw0930 I'm currently having the same opto issue in my ST. Did either of you find a cause to the problem?

If I may, I had to battle opto issues with star trek as well. It turned out that when I did a playfield swap, not one but two opto boards crapped out on me. They appear to be very fragile. If you lift up your playfield you will see 4 smallish boards underneath. Each board controls two different opto pairs. I had to replace mine.

Now I'm not sure if this is precisely the issue you're having, but it does happen often. I reached out to stern and they have them. It is worth a shot. What I did was tested which opto is failing for you, and trace that to the respective board underneath. Swap the bad board with a good one and see if the problem moves.

Now if they ALL are having problems, thenbid say it is somewhere in the back box.... and I would be of no help beyond that. Let us know.

That seems to be the case for me. It happens intermittently and I can't find a way to cause it to happen. When it does it seems to affect all the optos though. I was hoping someone else has figured out the cause.

I still have the game but I can't remember for the life of me what I did. I want to say I ended up replacing the board as the issue was not literally every opto going bad (although they are fragile)

this happens to my premium on the warp ramp. i find if i reseat the opto to the board, it fixes it for a while. but there is no rhyme or reason. my machine is on site and I'll get a call from a regular player saying that it's doing it again. I'll ask him to just power cycle the machine and it won't do it for weeks, other times it won't stop.
sometimes i go to give the machine a tidy up and a once over, and it's recorded a thousand warp ramp champion

Apologies for resurrecting this ancient thread but I've recently started battling this issue. The upper playfield optos powered by amplifier boards have been going haywire. It started off being intermittent, but now it's fairly reliably broken.

One interesting new bit of info is that they work fine… if only one of the four amplifier boards are connected at a time. Each one works fine independently, but as soon as I connect one of the other boards, they both start firing randomly.

I've reseated the connectors to the I/O board J13/J16.

Video of the switch test:

Picture of the J13 connector (is that janky daughter board normal?):

IMG_2042 (resized).jpeg

Solved: I realized that I didn't check the CPU board connections from the opto boards. I then noticed that boards 1,3,4 connect to J6, and board 2 connects to J1. So I connect 1 and 2 at the same time, and there was no issue. So it turns out that connecting any two boards that connect to J6 on the CPU board have an issue! So I check J6 on the CPU board (it's unlabeled, but whatever) and it wasn't properly seated! Pushed it in fully, reconnected the boards, and the game is as good as new. I suppose I should have read this thread more carefully.