RCD failure (the in-built test function that is)

If an instrument is "rode hard, put away wet", then there could be all sort s of failure modes from salts creep across some leads, corroded traces (esp ecially across SMT chip connections) and similar. Where the failure showed up is not necessarily the first-cause.

I have seen situations (as recently as this last weekend) where an individu al carried a tube tuner from his car to my clinic table in Kutztown for tes ting. What he did not understand was that it was a very hot and humid day, and he was dripping seriously through the cover into the guts. I did notic e the sweat and cleaned it off before applying power. But had I not noticed - between the salts in the sweat and them corroding traces, can you say *P OW*. Note that should there be some source of salts, these are naturally de liquescent - every time the humidity rises, the damage will go further.

Just a thought.

Peter Wieck Melrose Park, PA

I agree with Peter. 240/30e-3 = 8K BTW

Metal Oxide resistors usually totally break in half under overload.

Maybe they should have raised it off the board,

They could have not taken into account the voltage rating: See

I think that is the most likely, HV breakdown , perhaps 2x220K in series would not have failed but 1x450K would. The item was stored indoors , no damp involvement. But it seems a bit odd that dozens of times tested in use and then fails after an extended period of non-use. Perhaps stressing while in use, cracking the casing , then a film of mould or something organic can grow over the MO surface in storage.