On Jan 6, 8:50*am, Baron wrote:
D Yuniskis Inscribed thus:





Hi,

I'm wondering what the prevailing approach is when
it comes to dealing with kit that has been found to
have "bad cap-itis". *Particularly, PC's.

Do folks exploe the current operating conditions
of the machine *before* re-cap-ping (i.e., see
what supplies are affected, what sorts of ripple
is present, etc.)? *Or, do you just replace and
*functionally* retest (i.e., if you haven't
probed the circuit to get an idea for the exact
nature of the problem, probing afterwards at
that level of detail seems to be a contradiction)?

In particular, how do you know if the system has
been operating within "absolute maximum ratings"
while this fault has been present? *How do you
know the system's reliability/integrity hasn't
been compromised (so your "fix" is just a
band-aid)?

E.g., I've been recommending disposing of machines
with this problem. *The labor to re-cap just doesn't
make sense given the book value of machines that
exhibit these problems -- especially in light of
the fact that you can't be sure that the "repaired"
machine is really "100%" (maybe OK for a machine you
use informally at home, but would you want to *rely*
on it in a commercial environment?).

I suspect most machines are just recapped and re-used
but wanted confirmation or repudiation of that opinion.

Thanks!
--don

Its really a matter of horses for courses. *Some you do and some you
don't ! *I don't recall having further trouble with re-capped PC
mainboards. *Having said that not all clients will come back and
complain if the machine fails soon after its been repaired. *Its become
to easy to replace rather than repair nowadays !

--
Best Regards:
* * * * * * * * * * *Baron.

Had a PC mobo at work a couple years back that was not available any
longer but required as part of an expensive system. Replacing the bad
caps (and they were REALLY bad) has kept it working fine for 2 years.
Get a GOOD soldering iron like a Metcal. An inexpensive ESR meter is a
must. There are sometimes small ceramics in parallel with 'lytics and
these will 'fake out' the ESR meter. If a 'lytic measures bad, it's
bad but if it measures good, it may still be bad while measured in
circuit. Warming the cap while unsoldering it will make it read better
on the meter but very often gets much worse after cooling off. There
are some places where the caps need to be nearly perfect. A favorite
critical place is the filter in a SMPS on the 3.3 or 5V rail. The cap
may read 'OK' but that may not be nearly good enough. Don't use crap
grade caps either. For SM caps I like Panasonic FK or FP caps. Through
hole I start wit Panasonic FM, Nichicon HM.HN, HZ, PW and other low
ESR caps. Look for highest ripple current ratings.

Often there are a lot of caps same value and manufacturer. If some
read bad and others good, I change all of them since it's only a
matter of time for the rest to fail.

G²