Fault finding Thing’s Opto board

Back to the Thing optoboard this evening. I re-attached it to its connector (having used electrical tape to simulate an open Opto 1 switch) and turned the machine on and tested the switches. Sure enough the “left-outlane/Thing-up opto-switch” problem was still evident. However, now that the board was “free” I noticed that by simply moving the board I could get the opto switch to switch temporarily. Maybe this was related to the underlying problem?

I tried to identify which component on the board or wire leading to the board was causing this switching, but couldn’t locate it. Whenever I thought I had, it turned out it wasn’t in fact there. How frustrating! However, I then noticed that the 1N4004 diode on the board was uncomfortably hot! This definitely shouldn’t be the case. This diode (according to its spec) can take 1 Amp. On the board were two 470 ohm resistors, so even though I didn’t have the circuit diagram, I assume (although I may be wrong here) that the maximum current flow through the diode should be 12V/470ohm = 25mA. This shouldn’t cause a diode to overheat. I measured both resistors in situ and measured 470 ohm +/- 5%.

So I desoldered the diode from the board (burning my finger in the process) and measured its resistance in both directions. It seems to be OK, but this overheating is something I don’t like.

So I’ve now ordered some new diodes from Conrad and have tried to get a circuit diagramme of the optoboard from the forum flippertreff.de – but without any success to-date.

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