"M.Joshi" <
M.Joshi...@diybanter.com> wrote in message
news:M.Joshi...@diybanter.com...
It's almost impossible to say. SMPS repair is a black art. I do loads and
loads of them. Some are very well behaved repair-wise, and replacing a blown
MOSFET is all that is required. Or you can get them at the other end of the
spectrum where there has been so much collateral damage to the MOSFET
failing, that they defy reliable repair. And then there is every condition
between those two points ....
If a MOSFET has blown, there may well have been a cause, such as an
electrolytic with a poor ESR, but also, you can have a faulty control IC
that will do in the MOSFET. If the MOSFET failed for no particular reason,
it may well take out any series resistor between its gate and the control
IC, and / or any little diodes in the gate circuit. It also might take out
the control IC. Check also that the MOSFET source resistor has not gone
open, if the device failed D-S short.
Make sure that you determine which component let go of its magic smoke to
put the soot on those sm resistors, and make sure that you scrub all of that
soot off, using a solvent like IPA, applied with a toothbrush.
Finally, remember that switchers are EXTREMELY DANGEROUS. I would never
advocate attempting to repair one without it being plugged into a variac, in
turn plugged into a proper bench isolating transformer.
Arfa