TU56/TC11 restoration - Power supply question

Tom Peters tpeters at mixcom.com
Wed Mar 16 17:16:53 CST 2005


I replaced a electrolytic cap on a dead dog simple diode bridge, cap, and 
resistor PC board power supply once. There was an inductor on the board 
too, as I recall. Anyhow, I somehow managed to look at the polarity 
markings on the new cap twice and STILL solder it in backwards. It was 
marked on the negative side, where the old one had plus signs on the 
positive side.

Turned it on and BANG! the aluminum cap hit the ceiling above the bench and 
squashed itself flat. There was confetti all over the place. If I had been 
leaning over it, you'd be callin' me one eye'd Jack.

At 04:44 PM 3/16/2005 -0500, you wrote:
> >    Apart from the shock (and dangerous sudden-hi-energy discharge) risks -
> > one thing to be aware of when 'bringing up' large analog power supplies is
> > the condition where the filter capacitor(s), or other big electrolytic
> > device, develops and internal short, or loses it's chemical polarization,
> > and the esuing thermal rise causes the case to burst.  Most big caps have
> > built-in rupture vents, or a strategic 'crease' in the aluminum to keep
> > this from becoming an explosion - but I have been the unfortunate
> > recipient of more than one suddenly-exploding capacitor.
> >
> >    Not counting the sheer terror of having something go BANG! right 
> next to
> > you, the larger units can store considerable energy, both pressure and
> > electrical, and I've seen them do a lot of damage, especially the ones
> > mounted upside-down, which have a tendency to launch off the chassis like
> > a mortar shell and poke holes in walls.
> >
> >    Then there's the hideous mess that all the 'guts' of the cap makes when
> > they explode and puke up all over everything.
> >
> >
> >    So the moral of the story is to bring a long-dormant power supply up
> > slowly, using a variac and loads, and to be vigilant for any signs of cap
> > leakage, swelling, getting suddenly warm, or hissing sounds coming from
> > one.
>
>John,
>
>Thanks for the vivid visual images!  I suppose I've been lucky so far.
>Actually, most all of the stuff I've acquired has recently been powered on
>by someone else before it came into my hands, so if it was going to go
>BANG!, it probably would have done so before it came into my
>possession.
>
>I'd be interested in hearing any horror stories relating to exploding
>capacitors and more info on the proper caution that needs to be
>exercised when messing with old power supplies.
>
>Ashley


[Mind] It stands to the everlasting credit of science that by acting
on the human mind it has overcome man's insecurity before himself and
before nature. --Albert Einstein
--... ...--  -.. .  -. ----. --.- --.- -...
tpeters at nospam.mixcom.com   (remove "nospam") N9QQB (amateur radio)
"HEY YOU" (loud shouting)  WEB ADDRESS http//www.mixweb.com/tpeters
43° 7' 17.2" N by 88° 6' 28.9" W,  Elevation 815',  Grid Square EN53wc
WAN/LAN/Telcom Analyst, Tech Writer, MCP, Cisco Certified CCNA








More information about the cctalk mailing list