Elevated internal current leakage in electrolytic caps will heat them up.
The 'lytics with higher than normal internal leakage are the ones that
troubleshooters will miss, if the only tester they have is an ESR meter.

Leakage tests aren't performed in-circuit, therefore it's a good practice to
test new 'lytics when they're received and again before installing them if
they've been stored for long periods.

I don't do much repair work anymore, but had a habit of checking ESR (Value
and DA) and Leakage when new caps were received, and some new 'lytics would
fail Leakage tests occasionally, quickly getting very warm at their rated
voltage.

One of the most often repeated repair tips is to look for bulged tops and/or
signs of external leakage wrt electrolytic caps.
Generally, ESR checks are also advised, but electrolytic caps have other
faults and failures which rarely get mentioned.

--
Cheers,
WB
..............


"Jeff Liebermann" wrote in message
...

Probably to keep you from touching the can, which is probably
electrically hot. The life you save may be your own.

Electrolytic caps do not normally get hot. There is a temperature
rise equal to the ripple current times the square of the ESR
(equivlent series resistance). If the ESR is too high, usually due to
underspecifying the voltage rating or capacitor type, it will get
warm. There are derating curves for capacitors at various
temperatures. There are also lifetime prediction calculators which
include the operating temperature.

If you're shopping for a conspiracy theory, I guess the capacitors are
badly specified or picking up heat from adjacent heat dissipating
devices. A nearby resistor or heat sunk xsistor will heat up a cap
quite nicely. The shrink tube will have little effect on the cap
temperature. Black absorbs more heat, so it might be slightly warmer
from nearby radiation. At best, maybe a degree or two.

Pro audio is the same as consumer audio, except for the price tag and
the hype.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS