So my brother trades in old machinery, and he recently got two Bridgeport CNC routers from ' 89
Pretty early for CNC machines in fact. They had been in use until very recently at a university, where he picked them up himself.
Firing the first one up, after 20 minutes of fiddling with its mechanics, it released the magic smoke. And *lots* of it.
Being in an enclosure, it took some time to detect, and some more to respond and douse the fire, see for yourself.
Checking the 2nd machine, with a IR camera at the ready pointing at the same components, indeed, the capacitor themselves very quickly shot to 50C, and crawled to 80C in less then a minute. Normally not a really temp, but it was too quick, and nothing else was even getting warm yet.
Of course, it is always the question when finding a burned component: was this the cause, or a consequence.
Well, given
this video and
this thread, and the fact nothing else got hot, we think/hope this is the cause. They will be replaced for sure, all 12 of them.
Slightly worry however is that I measured the non-burned ones, and they measure a nice, exactly 0.1uF and 0mA leakage at 360V (that is as high as my leakage test setup goes)
So they measures very well. Except for the ESR, that seems a bit high to me, but I am unsure what is normal for a film capacitor like this.
So question: what would be a normal ESR value for a 80'ies RIFA 0.1uF non-X class film capacitor? Or any such film cap from that era?
I did check some equivalent modern ones, and they are lower, but I am not sure if I should compare 2010 devices to 1980 devices.
Thanks