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_replacement.htm
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.capacitorlab.com
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558