Is it worth it to replace the fuse in a PSU?

wumpus · Post by **wumpus** » Mon Feb 21, 2005 4:29 pm

I was working on my wife's computer the other day, and somehow I ended up with an exposed, 3-pin male fan connector hooked into the PSU, bouncing around the case.

Unfortunately I didn't notice this until it was too late: I accidentally grounded that 3-pin live connector on the aluminum case. ZAP! The system wouldn't power up after that. I later replaced the PSU with one I had on hand, and the system came up fine. I assume that I blew the fuse inside the PSU since it was the only component affected.

1) Is this a safe assumption? Is the fuse the only thing that got fried when I grounded the 3-pin fan connector on the case?

2) Is it advisable to open the PSU and replace the fuse? Is it worth it?

3) Where would I obtain an appropriate replacement fuse?

I suck at electronics, so any help from someone who has messed with PSU fuses before would be greatly appreciated.

sthayashi · Post by **sthayashi** » Mon Feb 21, 2005 5:22 pm

Depending on the PSU, you didn't even necessarily blow the fuse. I've done the same damn thing with my Seasonic PSU and flipping the main switch in the back to off and back to on worked (or was it pulling the plug and plugging it back. One of them was it).

mathias · Post by **mathias** » Mon Feb 21, 2005 6:17 pm

Likewise, I've short circuited the 12v and ground lines on a 350W Heroichi with a multimeter, it got knocked out, but just needed a few minutes to get back on its feet.

Oleg Artamonov · Post by **Oleg Artamonov** » Mon Feb 21, 2005 7:17 pm

Usually fuse blews only after the switching transistors or high-voltage capacitors fail, but not after short-circuit on output rail. So I think there was a failure of diode rectifiers, but not fuse; usually it's relatively easy to repair but you need some experience in electronics.

BTW, there is one standard 5x20 mm 250V fuse inside of PSU, rated at 6...10A (depends on total power of your PSU).

ChucuSCAD · Post by **ChucuSCAD** » Mon Feb 21, 2005 8:31 pm

wumpus wrote: 1) Is this a safe assumption? Is the fuse the only thing that got fried when I grounded the 3-pin fan connector on the case?

Possibly, does not hurt to check

wumpus wrote: 2) Is it advisable to open the PSU and replace the fuse? Is it worth it?

For a couple buck part it is well worth it.

wumpus wrote: 3) Where would I obtain an appropriate replacement fuse?

Take the fuse to your local electronics store, computer/electronic repair store, they should have one.

chucuSCAD

wumpus · Post by **wumpus** » Tue Feb 22, 2005 1:39 pm

Thanks for the feedback guys. I'll open it up, and take a quick look at the fuse. If the fuse is broken, I'll replace, otherwise I'll trash it.

Hate to lose a perfectly good PSU because I'm so clumsy, but I doubt the electronics repair (beyond simple fuse replacement) is worth the $40 it'd cost to replace.

larrymoencurly · Post by **larrymoencurly** » Tue Feb 22, 2005 3:01 pm

Every time I've found a blown fuse, I've found something else blown, too, usually the high voltage transistors. Fortunately the transistors and diodes are usually cheap and common, and replacements probably don't need to be exactly the same but just be the same general type with adequate ratings (volts, amps, etc.). You may even be able to use parts from old 200-300W PSUs their parts sometimes have amp and volt ratings as high as those found in some 400-500W PSUs.

Be sure to reinstall any electrical insulation between the part and heatsink, and don't use Arctic Silver or any other thermal paste containing pure metal powder.

ultraboy · Post by **ultraboy** » Tue Feb 22, 2005 4:37 pm

wumpus wrote:Thanks for the feedback guys. I'll open it up, and take a quick look at the fuse. If the fuse is broken, I'll replace, otherwise I'll trash it.

Hate to lose a perfectly good PSU because I'm so clumsy, but I doubt the electronics repair (beyond simple fuse replacement) is worth the $40 it'd cost to replace.

Before open it up, just try what sthayashi and mathias suggested. I think there's a high chance that it will still work.

Similar to you, I've grounded a live fan connector, psu shut off. Turned off the switch, took off the plug, reconnected it and it worked - that's even with a cheapo no name psu that came with case.

Jan Kivar · Post by **Jan Kivar** » Wed Feb 23, 2005 9:54 am

I'll chime in with the others: If the fuse is actually blown, it's normally a sign that something broke inside the PSU. All properly made PSUs have over-voltage/current protection on the main rails, and the breaker is auto-reseting (user just needs to power-cycle the PSU).

I've been in a situation where three ~identical computers blew out their PSUs within one week. I opened the PSU from the last one, and discovered that the fuse was blown. I replaced it with a proper one. The computer did start, but I didn't make it into the HW Monitoring in the BIOS when the fan started pushing out gray smoke out of the PSU. Nice effect; at that point I pulled the plug.

After the smoke had cleared, I checked what went wrong - one of the high-voltage capacitors had leaked. Luckily, there was no damage to the computer - I had plugged only the ATX connector, so maybe the HDs wouldn't have been so lucky.

Cheers,

Jan

Oleg Artamonov · Post by **Oleg Artamonov** » Thu Feb 24, 2005 6:14 am

All properly made PSUs have over-voltage/current protection on the main rails

Very often there is no separate over-current protection on each rail, only total PSU overload protection.

Is it worth it to replace the fuse in a PSU?

Is it worth it to replace the fuse in a PSU?

Re: Is it worth it to replace the fuse in a PSU?