The opto board A-15646 on my BSD is acting up. All of a sudden the detector switch is changing state randomly, but at other times also works correctly. It doesn't appear connector related, and moving the board to another machine, behavior follows.

I know replacements are available, but it looks like a simple board. Has anyone fixed one of these? Anyone recognize the symptoms and what component it might be? I'll get replacement chips and try replacing those: I'm suspicious of U2 or U1.

A15646-Schematic (resized).JPG

Thanks. The board has obviously been worked on before: has a different inductor than the clean example I have in the other machine, and also has a bunch of hot glue around the base, so previous repairer was aware of that problem.

I pulled out the logic probe and monitored U1 output P1. It is always correct and changes accordingly to opto beam breaking, even when the change isn't detected in switch test, so it seems the problem is on the right half of the schematic. Maybe Q1 or U2. Of course trying more probing was futile as I couldn't get it to fail any further.

I decided to take a closer look at the inductor, but removing all the hot glue was a pain: is there a good way to do this? There was a pretty big solder blob inside, so looks like broken leg was probably reattached on the top side with that, also explains why it wasn't sitting flush to the board and had all that hot glue.

Does anyone have a broken board they replaced and don't need? I haven't found any one place that has all the suspect parts.

Can anyone verify the inductor spec? Is it 10uH or 10 mH? Parts list says uH, schematic says mH. Part has no marking. I'm guessing it is probably 10mH as on the schematic.

There's other errors too, these should be:

R1 - 2.7k
R9 - 470
R12 - 0