On Sep 21, 9:44*am, Jeff Liebermann wrote:
On Mon, 20 Sep 2010 12:52:38 -0700 (PDT), Michael
wrote:
I've got a couple of Intel boards (D865PERL) that have one bad
electrolytic capacitor each. *One board stopped working; the other
still works, but has a bulging cap close to the CPU area. *(Pics not
yet available.)
My experience is that if you have the usual 8-10 identical capacitors
on the motherboard, and one is visibly defective, then the others are
highly likely to fail very soon. *I replace *ALL* the caps of a
specific type. *In particular, the caps around the CPU tend to die,
because of the heat and the high ripple current. *Typically, I'll
replace 10 to 15 caps.
Is desoldering these caps straightforward?
It varies. *Some boards are very easy to unsolder. *Others have
smaller holes for the leaded parts and are more difficult. *A vacuum
desoldering station is best. *Use plenty of heat and some liquid flux
so that you don't pull the plated thru hole out with the capacitor. If
you see a copper colored ring around a capacitor lead, you've probably
killed the board.
Any special precautions
multi-layered PCB traces?
If you don't have a tip that will heat both leads at the same time, or
don't have 3 arms so that you can use two soldering irons, all is not
lost. *I heat up one lead, and rock the capacitor in the opposite
direction. *After it moves a little, I heat the other lead, and rock
it in the opposite direction. *Don't use brute force or you'll rip out
the plated through holes. *Eventually, it comes out. *
One lead is usually grounded where the large copper area acts as an
effective heat sink. *This lead will be more difficult to unsolder
than the hot lead (usually +). *I use a big, wide (1/4"), hot (850C),
chisel tip. *Plenty of heat, and work fast. *This will take some
practice. *Find an old PCB and practice a little before attacking the
Intel motherboard.
Any special gotchas to keep in mind
when ordering replacement caps from say Mouser?
105C Low-ESR. *Watch the case dimensions and lead spacing. *If it will
fit, try to buy the next higher voltage rating. *I'm partial to
Panasonic but will use Rubycon. *Digikey, Mouser, and eBay (in that
order). *I sometimes use polymer caps as replacements, when the
motherboard is worth fixing and the customer doesn't care about the
cost. *Also, think about buying an ESR tester if you're going to make
a habit of this.
http://www.badcaps.net
http://www.afrotechmods.com/groovy/capacitor_replacement/capacitor_re...
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.capacitorlab.com
--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558
Thanks to all for your expertise in de-soldering...there is a world of
experience here, and worth much.
I have never had luck with braided wire...but evidently is works for
some. (I never have any luck with super-glue either!)