Just finished rebuilding a nice Judge Dredd. Ran through the tests after booting it up, and noticed that some optos were registering two different switches in the same column (highlighted).

I unplugged the connector from the opto board and connected the proper row/column wire with a diode, and only the correct opto triggered.

So I figured it must be an opto board issue, but then I realized that 77 isn't an opto. (or well, it is, but it's one of those U optos on a dedicated board, not one of the normal ones that use the opto board), and in fact that row isn't even connected to the opto board

After some troubleshooting I discovered that, if I unplug the trough optos, everything else functions properly. 71/61 only trigger 65/77 when the trough opto is connected.

All trough optos work fine, however the the issue changes depending on which trough optos are closed. To give one example, if a ball is in trough 6 (62), 49 will be off (as long as the actual 49 opto is in the right place). If I remove the ball, 49 turns on. if I move the ball to trough 5 (61), then 41 turns on.

The trough opto boards are repro

I'm probably missing some examples, but it's very hard to give a full listing of the issue because of all the optos involved...

Any ideas on where to look? My instinct is that something is going wrong with the trough opto making it respond to columns it shouldn't, but I don't understand why it would only affect other optos. I don't have any other compatible trough boards to swap

Capture (resized).PNG

More fun info:

I unplugged the column 6 opto board and then swapped it and another known good opto board with the column 7 opto board. All 3 worked the same.

In this simpler state with only the trough and column 7 opto board plugged in, I was able to get a reproducible test case:

if the crane opto is blocked:
- if the trough jam is blocked and no other optos are:
-- then the crane opto reads unblocked
- as soon as any other opto besides the trough jam is blocked:
-- the crane opto goes back to blocked

if the crane opto is not blocked:
- if any of the trough optos are blocked:
-- globe 2 flickers sometimes (otherwise not blocked)
- if any other opto in col 7 or trough jam is blocked:
-- globe 2 is blocked
--- if globe is rotated while in this state:
---- globe 2 unblocks and blocks as normal
--- when not in this state globe 2 is stuck unblocked

12VU on driver reads 13V. I checked it at all the optos and it's also 12V+. Trough boards are repros with all surface mount stuff so it's sorta hard to investigate, but I've got the trough removed so I'll take them off and take a look

Realized I could swap the trough opto from my Demo Man in for the one in JD even though they were different part numbers (a-16926 vs a-17981), so I plugged that in and the issue disappeared. Looks like this repro board has an issue...

They were in it when I got it. Emailed Great Lakes Modular in case this is a known issue, waiting to hear back. Supposedly the game played fine before it was disassembled, so I'm not sure if something went wrong somewhere or if the issues just never became apparent in gameplay. I only noticed it because I couldn't get the dead world mod to work quite right. It would stop about an inch off from the crane sometimes but not others, but would unload the ball successfully after a few tries. Works solid without the trough plugged in, but maybe they just never noticed.

On original boards I would have assumed it was the comparator but I don't even see any chip on these with that many inputs.