Last one for now. This is from my own machine and it was just starting to suffer battery corrosion.
After reading on here about vinegar washes I dabbed on a little on the worst areas as a test. Bad move! It lifted all the silkscreen. I think I'll stick to IPA in future.
As it goes, by the time I'd got all the corrosion off, a lot the surrounding silk screen would have gone anyway I suspect.
Components removed and halfway cleaned the top side. Resistor R40 literately fell apart during desoldering, that would explain the fault I was getting of intermittent sound. The green LED had stopped working too due to corrosion ingress I suspect.
Bottom was OK.
That's the cleaning finished. Quite a bit of the solder mask had lifted too.
New solder resist painted on.
Finally new components replaced as the resistors and diodes all had corrosion on their legs.
Plugged it in and it all works. Phew!!
Hopefully it should last another 25 years.
PS:
If you look closely you might notice I'd put a diode and a couple of resistors in the wrong place. Doh!
I did spot it before it left the bench though. It's been a long day.
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