Another dead kairn and seeing the signs already (gulp):
Yep we have sparklies! But not the worst I’ve seen.
it just travels everywhere mainly along the negative current paths. Typically happens when battery is flat (not been plugged in for a long time)
Cleaned up with water, neutralised with citric acid, and repair any traces that have been completely dissolved. It gets inside solder too, and makes it almost impossible to melt as it destroys the wettability with an instant black coloured oxide layer. Eventually can get through with plenty of acid flux but it’s not easy and preferable to leave such soldered joints alone in severe cases as long as electrically sound.
The corrosion even manages to migrate inside the power LED and tends to destroy them, so that was replaced too.
New battery fitted:
And all good:
