Electronics > Manufacturing & Assembly

Green shmutz on trimpot screwheads

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we have seen the problem with Bourns and BI Tech. Which leads me to tend to exonerate the trimpot manufacturer.

The jumper pin to the immediate right of the "LIN" pot looks tarnished, although this could easily be a reflection in the photo. I would perform an extremely careful and thorough inspection of the entire PCB. Any other discoloration might indicate exposure to a corrosive environment during or after assembly.

Looks like corrosion to me, the locking/tamper seal goop has a certain look to it and this is not that.

you need to take a close picture with a magnifying glass and to test if its tarnish scrape some off and put it in hot vinegar (microwave styrofoam cup is fine) or lemon juice. it will dissolve if its tarnish.

the only thing I can think of that might be causing film tarnish like that is a spray flux process which has a acidic enough flux to get brass to corrode but it might not effect common tin plated parts. all fluxes have a acidic nature (when hot) because that is the only thing that will get rid of metal oxide. The idea for electronics flux is that at room temperature it is not acidic or nearly non acidic so it becomes inert after soldering.

I see there is SMT parts there too. Manufacturers do alot of creative things with flux to get boards that solder together right.

the part with the label PS looks very much like oxidized metal

Here's a closeup. FWIW, I'm coming around to corrosion sort of thing. Like a patina.


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