Two days ago, when applying +5V to a couple of LEDs, I measured an unexpected drop in the applied voltage of more than 0.3V.

After opening the PSU, checked the fixed regulator in charge, a 340 - 7805, and found it still happily giving the same 4,99V as when assembled 10 or 15 years ago.

I found that the reason of the voltage drop was the (multi-filament) cable which, over most of its length, after peeling it progressively, was seen covered with a sticky green / dark green substance.

Even the crocodile, after retiring the rubber-like protection was full of that gummy thing.

I recall having seen something like that before, when salvaging components from old (tubes era) equipment.

What is it? When, where and why to expect that happening again?

 

Copper oxidation? Use marine grade wire?

 

The green color comes from copper compounds, but where does the slime come from?
I don't know. I only know you have to replace any wire that has slime in it.

 

The green color comes from copper compounds, but where does the slime come from?
I don't know. I only know you have to replace any wire that has slime in it.

Binned on the spot.

 

Green slime is sometimes seen on 1970s PVC insulated cables in the UK, it's believed to be the plasticiser reacting with the copper but on our thick solid-core mains wiring it doesn't affect the resistance noticably. I imagine a stranded cable suffering the same might be quite different.