Corsair HX620 popped

[ntoskrnl]

My trusty old Corsair HX620 blew the fuse today when I tried to power up my computer. The power supply is from 2008 (manufactured in late 2007 according to the stamp on the PCB). There was no audible or visual spectacle at all.

I opened it up of course, and there don't seem to be any popped transistors, burn marks or other visually obvious failures. All the capacitors seem fine as well (they're quality stuff). The fuse and bridge rectifier measured good, but I found a heatsinked three-legged TO220 component on the primary side that appears to be shorted. My search was by no means exhaustive so there could be other problems as well.

The shorted component is in a tight space, so I can't read its part number. However, the one next to it might be identical, and it's a 24N60C3 (datasheet). (This review indeed shows there are two of those.)

What could cause this? If I replace the shorted FET, is it likely to fail again? Or maybe other components are also dead?

I can't find an exact replacement for the FET, but Farnell stocks a suggested replacement part that would cost me about 6 € apiece. I'm not too thrilled about replacing it though (with great difficulty using a 15W soldering iron) just to find that half of the other components in the PSU are dead too, so at this moment I'm contemplating on ordering a new PSU.

[stj]

Re: Corsair HX620 popped

dont trust farnell, compare the datasheets.

[Per Hansson]

Re: Corsair HX620 popped

That is part of the APFC circuit, you could disconnect it since you are in Finland so you run from 230VAC, the PSU should be able to operate fine like this.
Just don't try to power it from a ~110VAC circuit because the low voltage going to the bulk capacitor will not be enough.
If you know what platform it is someone should be able to come up with a schematic that is at least similar, so it would be easier to figure out what if anything needs to be rewired...

This might give a rough idea:
https://www.badcaps.net/forum/showthread.php?t=50509

[ntoskrnl]

Re: Corsair HX620 popped

Hmm, I guess a bit more harmonics in the distribution grid doesn't matter that much.

The review I linked earlier says it's a Seasonic S12. I wonder what I should disconnect; is it enough to cut the legs on the APFC FETs or should I also disable the APFC chip?

[ntoskrnl]

Re: Corsair HX620 popped

So I did actually find a burnt component. It's a green disc shaped one marked TR301 (an MOV?), and it's sandwiched right between the main filter cap and the main transformer. There's very little room around it. I'm going to try desoldering it now.

edit: It's a thermistor apparently: http://www.jonnyguru.com/forums/showthread.php?t=11537 I guess something else is shorted as well then.

edit: There's no way I could find a replacement thermistor without knowing its specifications. Can I just cut the legs of the shorted PFC FETs and replace the thermistor with a jump wire? I guess this will eventually blow the PFC diode; what about jumping the diode as well now that PFC doesn't work anyway?

[budm]

Re: Corsair HX620 popped

Can you still read the number on that NTC? Dia. of that NTC, 15mm, 20mm?
the power supply may run at 330VDC without the PFC Voltage booster but it will draw more current to maintain the Output power.

[momaka]

Re: Corsair HX620 popped

Can I just cut the legs of the shorted PFC FETs and replace the thermistor with a jump wire?

Yes.
The large coil in the APFC should somewhat limit the inrush current anyways, so the lack of thermistor probably won't damage anything.

what about jumping the diode as well now that PFC doesn't work anyway?

Yes, you can jumper the PFC diode as well. In fact, that will be even better for the efficiency of the PSU (one diode drop less on the primary side. Yay!)

If the PSU runs like that, I say don't even bother fixing the APFC. Just replace the thermistor and be done with the PSU.

[ntoskrnl]

Re: Corsair HX620 popped

Alright, so I desoldered the burnt thermistor (it was very "crispy" and fell into little pieces when I removed it, so I couldn't read any markings, but it was perhaps around 10mm in diameter), cut the legs of both PFC transistors, and added a jump wire from the anode of the PFC diode to the main capacitor. It works fine now.

I think I know what went wrong too. I use a power strip with a switch to turn off all computer related devices. I've been hearing a muffled "pop" every now and then when closing the switch, for the last year or so. I thought this was due to arcing in the switch or something, but now that I think of it, it's probably been the thermistor cooking and popping all along. Eventually it decided to throw in the towel and fail open, and when the PFC transistors started switching, the energy in the coil had nowhere to go so it killed one of the PFC transistors.

Thanks for all your input.

[TELVM]

Re: Corsair HX620 popped

... you can jumper the PFC diode as well. In fact, that will be even better for the efficiency of the PSU (one diode drop less on the primary side. Yay!) ...

Momaka you are referring to the APFC boost diode, like the one at the center of this pic, right?:



http://www.hardwaresecrets.com/anato...er-supplies/6/

[budm]

Re: Corsair HX620 popped

There are two Diodes that need to be bypassed, the one on the heatsink is the boost diode.

[momaka]

Re: Corsair HX620 popped

Momaka you are referring to the APFC boost diode, like the one at the center of this pic, right?:

http://i.imgbox.com/9SUE0pWO.png

http://www.hardwaresecrets.com/anato...er-supplies/6/

Yes, exactly!

There are two Diodes that need to be bypassed, the one on the heatsink is the boost diode.

I would advise *against* bypassing the second diode (i.e. the one that is not used for APFC boosting). That way, current on the primary will only go through the APFC boost coil, essentially serving as a single-mode choke for extra EMI/RF filtering. Actually, with that other diode in there, this won't work too well either, so I guess it doesn't really matter. You can either remove the second diode completely or short it.