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Removal of motherboard electrolytic caps

Discussion in 'Electronic Repair' started by David Sewell, Oct 22, 2004.

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  1. David Sewell

    David Sewell Guest

    I have a motherboard that has three electrolytic caps that are bulging. I
    have a 40watt iron with a chisel shaped bit that is just wide enough to
    cover both wires of each capacitor at the same time. Would this rating be
    enough to safely remove these by just heating and pulling them or am I
    likely to cause damage by insufficient power. Each capacitor is 330uf/25v.
    Hope that's enough info...

  2. CFoley1064

    CFoley1064 Guest

    Subject: Removal of motherboard electrolytic caps
    Hi, Dave. A heads-up here -- motherboards are multi-layer, and yanking the
    leads out can result in tearing the connections between layers.

    It's far better to cut off the top of the cap and gently heating each hole
    individually. Very gentle here -- don't pull. It should practically come out
    on its own.

    Also, a 40 watt iron is a little heavy for PCB repair. Most people use around
    a 25 watt iron for PCB repairs.

    One other thing - don't just use any electrolytic cap here. You need an
    aluminum electrolytic with low ESR, or it may be as bad or worse than nothing.

    Good luck
  3. David Sewell

    David Sewell Guest

    Thanks for that Chris,
    I recall servicing GEC brand tv's many years ago, and they had double-sided
    print, and they were a bit of a pain. That was a cinch compared to a
    motherboard!! What made me think of a high power iron was because of
    something I read in a forum about the solder on a motherboard being of a
    higher melting point than normal. I had already tried an ordinary Antex
    25watt iron and braid but it did not seem to be melting the solder - then
    again the thing is so small my old eyes may have been deceiving me! Never
    thought of cutting the cap itself. What sort of tool do you recommend and
    do you mean the part of the cap as close as possible to the wire end?
    Many thanks,
  4. What made me think of a high power iron was because of
    The problem with using too hot of an iron is that the heat, if too high, can
    cause damage to the pads.

    Try a 30 watt iron. - Reinhart
  5. Johnboy

    Johnboy Guest

    To do it right, you really need a new tip and a good de-soldering
    I use a Pace, have years of experience, and still booger up a board
    now and then. Multi layer boards are built real well, but you still
    to do it correctly. See if one of your electronics pals has a
    setup, and will do it for you.
  6. David Sewell

    David Sewell Guest

    Thanks guys (or gals!) for your help. I will seek extra help from my local
    spares supplier regarding desoldering. But not too optimistic as they are
    geared towards the old traditional style tv spares and servicing.
    Great help anyways,
    There you go
  7. Wayne

    Wayne Guest

  8. CJT

    CJT Guest

    FWIW, I recently did that job, and ended up drilling out the old leads.

    BTW, use low ESR 105 degree C caps.
  9. Lionel

    Lionel Guest

    Kibo informs me that (CFoley1064) stated that:
    Good advice.
    Although I've found that 25W can be a little weak for working on
    ground/power plane pads on multilayer boards, but as you said, 40W is a
    little risky. Generally, it's best to use a good soldering station for
    this sort of job, rather than a general-purpose iron.
    A tantalum cap would be even better in this application. If you're
    buying parts from a hobbyist shop, it can be quite difficult to find out
    the the ESR rating of their electros, but standard tantalums are certain
    to be correct.
  10. David Sewell

    David Sewell Guest

  11. Lionel

    Lionel Guest

    Yep. ;)
    That's incorrect. The reason it seems that way is because motherboards
    have huge ground & power planes on their own layers within the PCB,
    which tend to act as heatsinks when you attempt to solder/desolder any
    pins that connect to power or ground. Consequently, a light duty iron
    will lose so much heat to the planes that the joint won't heat up enough
    to melt the solder all the way through. Ideally, you need to use a
    temperature-controlled iron with a heavy tip (I use a traditional,
    ultra-reliable Weller TCP station myself, & strongly recommend them). If
    you don't have access to a real iron like that, the next best thing is
    to use a heavier standard iron - perhaps 30-40W or so - but you'll need
    to be ultra careful not to damage the pads or cook the the surrounding
    The standard tool is a small pair of side-cutters, but I usually remove
    electros by heating both pads with a blob of solder covering both, &
    *gently* wiggling out the cap at the same time. (If a gentle touch
    doesn't move the legs, the joints aren't yet hot enough - *do not* force
    them, or you'll destroy the through-hole plating!)
    Use whichever method you find easiest, with care, either will do the job
  12. Art Todesco

    Art Todesco Guest

    I've alway done this by 1st heating the solder with a good temperature
    controlled iron, and then sucking out the majority of the solder with a
    plunger-type sucker. There are special static free solder suckers. The
    iron tip should be clean with a nice thin, shinny coating of solder.
    Sometimes to get the heat transferred fast, you much 1st add a bit of
    fresh solder (with flux core) to help conduct the heat. This is
    especially true on power or ground nets were there might be a lot of
    copper on the board drawing away the heat. Once most of the solder is
    gone, I touch the iron tip to the wire or pin (for a through-hole IC) on
    the non-component side of the board, and try to push it away from the
    hole walls. Many times, especially with a 2 terminal device, it will
    fall out rather easily. Even through-hole IC will usually come out
    without board damage.
  13. James Sweet

    James Sweet Guest

    If you try it with a 25W you'll never get them out, more likely you'll
    overheat the board from having to keep the heat on it so long and the pads
    will rip right off. I use a 140W Weller soldering gun for these, it's the
    only way I've found to reliably heat the capacitor lead quickly enough to
    remove it from the multilayer board without tearing things up. Conventional
    rules do not apply here.
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