Could a transistor going flaky and overdriving capacitors cause them to
swell? How about causing one of them to explode?

Just wondering what caused the systemic failure of the power supply PCB I am
looking at.

Thanks,

Dave

Dave wrote:
Could a transistor going flaky and overdriving capacitors cause them to
swell? How about causing one of them to explode?

Just wondering what caused the systemic failure of the power supply PCB I am
looking at.

Thanks,

Dave




Capacitors just fail, it was probably one of the millions made with the
faulty electrolyte several years back.

"Dave" wrote in message
...
Could a transistor going flaky and overdriving capacitors cause them to
swell? How about causing one of them to explode?

Just wondering what caused the systemic failure of the power supply PCB I
am looking at.

Thanks,

Dave



For some strange reason, switchmode power supply designers have a
predisposition towards putting any and all critical electrolytics, as close
as possible to any sources of heat that are also on the board.

This has the effect that from day one of the power supply's service life,
its electros are being baked by external heat radiation from these sources.
Now add to this that the caps that are fitted are often only 80 degree
types, and are not of the best quality low ESR type specially specced for
switchers, and you now have self-heating to add to the equation, when they
start trying to handle the large high frequency ripple currents that many of
them will be required to do, as part of their job. Now compound the
situation even more by putting the supply in a unit tht's designed for its
external appearance, rather than airflow around its inside, and finally put
it in a glass fronted cabinet with poor ventilation in your lounge, and you
can see why the electros will start to fail and eventually bulge.

Depending on where in the circuit the cap is, the failure may cause anything
from a simple supply shutdown, to a catastrophic cascade failure, involving
semiconductors and resistors on the supply itself and, sometimes, serious
failures of LSIs located elsewhere in the equipment, due to either the power
supply's regulation going out of the window, or huge high frequency ripple
voltages on the rails, that these devices just can't handle.

These days, this type of failure is the 'bread and butter' work of most
independent service engineers, so this mechanism of failure (which is not
confined just to power supplies either) is very well understood by us all.

Arfa

Thanks, all, for the input. As the result of all your feedback,I feel I
have a much better grasp of what I am likely dealing with.

Much appreciated...

Dave

"Dave" wrote in message
...
Could a transistor going flaky and overdriving capacitors cause them to
swell? How about causing one of them to explode?

Just wondering what caused the systemic failure of the power supply PCB I
am looking at.

Thanks,

Dave

Meat Plow wrote:

I see/read a lot about SMPS failures and my educated opinion is that they
are just very hard on components. Electrolytic caps are more susceptible
to problems with heat which they seem to endure in an SMPS because of
their physical placement next to heat sources. It also depends on the
quality of the caps. Vendors sometimes use less than desirable quality
caps that swell and blow for seemingly no detectable reason.

I had a video card blow 3 out of 6 electrolytics (unknown brand) in
less than one year of use:

http://farm3.static.flickr.com/2350/...2c511a5a_o.jpg

OTOH the power running this computer is nine years old and doing fine
(Japanese caps).