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Electrolytic caps ...

Discussion in 'Electronic Repair' started by Arfa Daily, Nov 11, 2008.

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  1. Arfa Daily

    Arfa Daily Guest

    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 ...

  2. Arfa Daily

    Arfa Daily Guest

    Oh you are a jolly little tinker, Jeff ... !! d;~}

  3. Franc Zabkar

    Franc Zabkar Guest

    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
  4. Arfa Daily

    Arfa Daily Guest

    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 ... :)

  5. hr(bob)

    hr(bob) Guest

    Can you use some other words for "knackered" that those of us on the
    west side of the big pond would understand???

    Bob Hofmann
  6. N_Cook

    N_Cook Guest

    Can you use some other words for "knackered" that those of us on the
    west side of the big pond would understand???

    Bob Hofmann


    knackered over here has the same meaning as the name that appears on Homer
    Simpson's favourite/favorite cans of beer.
    But does "duff" have the same maeaning in USA?
  7. Franc Zabkar

    Franc Zabkar Guest

    My current iron had an intermittent heating fault from new. Ironically
    [pun intended] the problem was a dry solder joint. I fixed it by
    holding the joint closed with an insulated rod and allowing the iron
    to warm up. I then unplugged it and used the residual heat to reflow
    the joint.

    In your case I would have held a good cap in parallel with the bad one
    until the tip warmed up.

    - Franc Zabkar
  8. jakdedert

    jakdedert Guest

    How 'bout just plain ol' wore out....?

  9. Arfa Daily

    Arfa Daily Guest

    Can you use some other words for "knackered" that those of us on the
    west side of the big pond would understand???

    Bob Hofmann

    Given the context, I'm sure you could work it out, Bob. However, see and

    for descriptions of this word, common on the east side of the pond. You will
    see that there is an entry from the American Heritage Dictionary, so I am
    surprised that you have not come across this word, and the obvious
    connections to a 'knacker's yard' where worn out horses used to go, given
    that the primary mode of transport in the great US continent, was the humble
    horse, not so many decades ago ...

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