So the outdoor thermometer hanging over my desk became very, very faint, which suggested it was time for a new alkaline cell. The last time that happened, the insides were pretty bad, so I expected the worst, but, surprisingly, neither the cell nor the negative contact spring were corroded. So I popped in a new cell, buttoned it up, and … it didn’t work. At all. As in: blank display.
Taking the back off revealed the simple cause:
Evidently, the negative terminal wire had corroded completely through and popped off when I replaced the cell. There’s plenty of green-blue corrosion on the terminal inside the case, where it can’t be seen from outside; three years ago I cleaned up both the outside and inside, so this is new news.
The negative wire was discolored all the way from end to end and couldn’t be soldered. I think the corrosion products are just slightly hygroscopic and wick their way along the copper strands inside the insulation: the solder pad on the circuit board was also discolored.
I removed the terminal, neutralized the alkaline corrosion, ran it through an Evapo-Rust bath, scrubbed it clean, installed it, replaced both the positive and negative wires, resoldered everything, and it works perfectly again.
This can’t go on, can it?
The Smell of Molten Projects in the Morning 