"Franc Zabkar" wrote in message
...
On Tue, 11 Nov 2008 16:19:44 -0000, "Arfa Daily"
put finger to keyboard and composed:

Here's a good example of what we often talk about on here with regard to
electros that are normally powered all the time, or at least every day,
and
then fail immediately, after a period of non use.

One of my bench irons, is a temperature controlled Antex station with a 50
watt handpiece. Up until when I went away on holiday a couple of weeks
ago,
it was on every day for 10 or more hours, and worked perfectly. Monday
morning, after returning from 2 weeks away, I stumbled jet-lagged and
grumpy
into the workshop at 9am and switched the benches on. The display on the
Antex was going berserk, with the temperature figures flickering and
flashing. The up / down and menu buttons did nothing. So, first and much
un-needed job was to find out what had gone wrong with it. When I opened
it
up, there was an unexpectedly complex board inside (considering that this
is
not an expensive tool), and there, right by the side of a regulator on a
heatsink (where else, of course ... !!) was a 470uF 40v cap. It looked
physically ok. No discolouring of the sleeve, no leakage of electrolyte,
and
no bulging, but when I ran the ESR meter over it, it went over 40 ohms.

A new cap of course cured the problem. I guess with its location being
next
to a hot component, it had been on its way for some time, but it didn't
get
to the point of causing any actual trouble, until it had not had volts
across it for a couple of weeks.

In this particular case, it was merely an annoyance to have to repair it
before I could start work. No damage had occured because the circuitry in
the power supply is all linear. However, it lets you see how these cascade
failures in switchers occur, when people power down their DVD player or
whatever to go on holiday, and then when they come home and repower them,
magic smoke gets released ...

Arfa

I notice you referred to it as "one of my bench irons". It would have
been interesting had it been your only iron. ;-)

- Franc Zabkar
--

Ha! Yes, I suppose it would ... Fortunately, I have another fixed temp
Antex, and the Weller with the permanently burnt-out tip (see thread from a
few weeks ago)

I don't know why I took the holiday in the first place. I've been back a
couple of days, and feel as knackered now as before I went. Roll on
Christmas ... :-)

Arfa
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