A friend asked me if i could have a look at this PSU from his HP desktop SFF computer as a new compatible psu cost more than his old PC.
The symptoms are the computer won't start and the power on led blinks, after a visual inspection most caps need to be replaced, seemed quite straight forward, replaced the 5VSB caps first and tested if there was stand by voltage.... nope... checked the main cap and there was 0V something doesn't match with what he told me......
F1 was blown and Q4 (PFC mosfet) had all pins shorted, replaced the parts and checked for shorts, i didn't find any broken silicon so i tested again, now i had 5Vsb, decided to try if the main PSU worked... bzzzzzzz pop! F1 and Q4 were dead again, this time shorted source to drain (my fault, i should have used the lighbulb)
Time to desolder and test components:
- Q4 is a toshiba K2698 i replaced it with an used ST W21NM50N (it has better specs and it was what i had at hand)
- PFC diode D2 (S1TH8S06D) OK
- main mosfet (toshiba k2611) OK
- 5Vsb fet (AP02N90I)OK
- PFC coil looks fine, no burn marks 1.5 Ohms and around 1830uh
- Gate driving transistors of the PFC aren't shorted (Q7-Q9) so i guess they are OK
I have found two problematic components R2 and R14 (1w? resistors, ignore the black coating of R14)
R2: brown-orange-silver-gold-green --> (13.8 Ohms 0.5%) reads 0.9 ohm
R14: orange-orange-silver-gold-green -->(33.8 Ohms 0.5%) reads 1.1 Ohm
Can a wirewound resistor fail shorted or am i reading something wrong? any suggestions?
The symptoms are the computer won't start and the power on led blinks, after a visual inspection most caps need to be replaced, seemed quite straight forward, replaced the 5VSB caps first and tested if there was stand by voltage.... nope... checked the main cap and there was 0V something doesn't match with what he told me......
F1 was blown and Q4 (PFC mosfet) had all pins shorted, replaced the parts and checked for shorts, i didn't find any broken silicon so i tested again, now i had 5Vsb, decided to try if the main PSU worked... bzzzzzzz pop! F1 and Q4 were dead again, this time shorted source to drain (my fault, i should have used the lighbulb)
Time to desolder and test components:
- Q4 is a toshiba K2698 i replaced it with an used ST W21NM50N (it has better specs and it was what i had at hand)
- PFC diode D2 (S1TH8S06D) OK
- main mosfet (toshiba k2611) OK
- 5Vsb fet (AP02N90I)OK
- PFC coil looks fine, no burn marks 1.5 Ohms and around 1830uh
- Gate driving transistors of the PFC aren't shorted (Q7-Q9) so i guess they are OK
I have found two problematic components R2 and R14 (1w? resistors, ignore the black coating of R14)
R2: brown-orange-silver-gold-green --> (13.8 Ohms 0.5%) reads 0.9 ohm
R14: orange-orange-silver-gold-green -->(33.8 Ohms 0.5%) reads 1.1 Ohm
Can a wirewound resistor fail shorted or am i reading something wrong? any suggestions?
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