On Fri, 2 Jan 2009 18:17:41 -0800 (PST), wrote:

: Just out of curiosity, has anyone tried using an infrared
:thermometer to try and find bad or failing caps. I did a quick search
n the on the internet and found units you can get for as little as
:$20. The spot size is very small and I believe the top of the cap is
:an ideal target. Could use a black sharpie to make a small black spot
:for even better measurements. A SMPS cap which had a High ESR should
:read high in temp, might be more sensitive than using your finger to
:test for temperature. An open or failed cap should read low. Of
:course the unit being tested couldn't be completely dead. If it
:worked one nice feature would be being able to identify bad caps
:before even removing the PC board.


Since electronic equipment (particularly SMPS) will generally run fairly warm
under normal loading the whole unit will become warm throughout after some time.
In order to determine a bad cap using thermal means would require the background
component temperatures to be used as a base reference and discounted from the
temperature of the cap being tested. It would be somewhat equivalent to sticking
a finger on each cap to see if it was warmer than the average temperature of
other components - but I wouldn't recommend this in working equipment.

In some circuits (SMPS) a bad cap will prevent the unit from operating at all
and then you have no way of measuring by thermal means.

Not a valid faulty cap finding method IMO.

:
: The power dissipated in the cap should be proportional to the
:increase in ESR ,the temperature increase should be on the fist order
:equal to the power dissipated in the cap. So if the original
:temperature rise due to the new caps ERS was 1 degree C and the ESR
:increased by a factor of 10 the old caps temperature should be about
:10 deg higher, easy to measure.
:
: Might be able to find bad IC's as well. Perhaps the increase in
:sensitivity using this device would help find other failing or failed
:components as well. Might also be useful in identifing failing or
:failed components in very high voltage circuits. Those components you
:would not want to touch with power on.
:
: Don't know if the idea has any merit but thought I would mention it.
:
:Gordon ,