Samxon GF caps

[c_hegge]

Yes. Check the PFC Transistors and switching transistors. It sounds like one of them is shorted. A shorted coil is also a possibility.

[Pentium]

Will do! Input coil, PFC coil, or both?

[c_hegge]

I meant the PFC coil

[Pentium]

Cool, thanks for the reply. Noob question. Never checked a PFC coil before, would I be checking resistance?

[c_hegge]

You can't test a coil with a DMM. It's the inductance that you would need to test. If it still blows up the PFC FETs after you can verify all of the other parts are fine, then I would try another coil.

[Pentium]

So I pulled the first of the 3 heatsinks, the PFC diode tested good. The two power MOSFET's on the other hand, both shorted! They're FB20N50K's. http://www.mouser.com/ds/2/427/sihfb20n-107413.pdf

So I would guess that the PFC circuit is intact. I just need to find suitable replacements for those blown FET's.

Would it be a good idea to check the other silicon?

IMG_20130619_123326_693.jpg (248.36 KiB) Viewed 22727 times

IMG_20130619_123423_250.jpg (253.37 KiB) Viewed 22727 times

That PFC diode is an STTH8R06D

[c_hegge]

Those MOSFETs are the PFC Transistors. Before you replace them, check the PFC Cap and switching transistors. Samxon PFC caps aren't particularly known for problems like CapXon, but it doesn't hurt to check anyway. If it still blows up the PFC transistors, then the PFC Choke and/or another small component could be at fault.

[Pentium]

Cool, will do. In your opinion, is it most likely just the silicon that's bad? And would I need direct replacement parts or should I just try to match the specs? Thanks for the help. Oh and the PFC cap tested good, 306uF

[Pentium]

Wow, all of the switchers tested bad on the second heatsink. Is it possible that the PFC coil could kill all the silicon on the primary except for the PFC diode?

[c_hegge]

All 3 of them? If the 5sb one is blown as well as the main switchers, then it seems like something in the PFC circuit is responsible. A shorted coil could be an explanation. You might have a hard time finding one, though.

Also make sure no other resistors are open and no other diodes are shorted.