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PSU keeps blowing

Last response: in Components
February 28, 2011 9:21:00 AM

Hi. Just over a week ago our power went down in our front room (which is were the PC is). I checked and found that the fuse for that room only had tripped. So, switched it back on. After about 5 minutes there was a loud bang and everything went dead again. It turns out that the power supply in the PC had blown. however, the machine wasn't switched on. The PSU was on, but not the machine itself (not sure if this makes a difference to the diagnostics?). I plugged an old PSU in, but the second I switched that on it sparked and died. Now, both the PSU's were old, over 5 years. However, the replacement I ordered worked initially until I was screwing the hard drive in place (it only had one screw for some reason, so decided to put a second one in), got a spark and it died - the PC was switched off (I'm not that stupid....) but the PSU was on (so maybe I am that stupid...). Checked the PSU in my old machine and still didn't work, so sent it back from whence it came.

Now, I would surmise that me messing about with the screws caused a short and blew the power supply (oh, the mains didn't go off at this point, just the PSU). But, would that have damaged anything in the machine which would then cause a PSU to blow again?

The replacement arrived this morning, plugged it into the old machine (which is just motherboard, CPU and sound card - no onboard graphics etc) and the motherboard LED came on, so I knew the PSU was at least working although I didn't power up the machine. Plugged it all back into the main machine, switched it on and it instantly blew and tripped the switch.

I initially thought it could have been the power cord, but I used a different one for each replacement (the initial new PSU blew the plugs fuse when it blew itself) so not sure if that has caused it.

I am going to get another replacement, but I am unsure what's causing the blowouts and I don't really want to blow another PSU. Ebuyer may accept a second faulty return - but a third....?

As far as I can tell it must be one of the following:
Dodgy PSU's (assuming that the initial issue was simply due to age etc)
Something is knackered in the machine and causing the blow outs (motherboard, Graphics????)
An issue with the house electrics.

I should also add that the PC is connected to an extension lead with a build in circuit breaker/tripper thing but nothing suggests this has noticed an issue. I have two, and each blow out was plugged into a separate extension lead.

The new PSU was a 500w unit, as was the previous PSU which had lasted a good many years, so I doubt it's that. However, just in case here is my system:

AMD 64 2.4ghz (not that I have been able to get it above 1.6ghz!!!)
Creative Audigy2 Z sound card
Radeon 16500 graphics card feeding a HD TV (VGA) and a 19inch monitor (dvi)
2x SATA HDD - 500gb & 750gb
1x DVD RW Drive
Plethora of usb connected devices but all powered via a exteral powered hub

I have had a quick llok at other issues with blow-outs on this forum but couldn't see anything which would help here. Iit could be an overload on the circuit board to the house i suppose, but in between the initial blow and todays we replaced a Netgear Wifi and seperate VM Modem with a VM wireless hub - which I assume would cosume less power as it's one device replacing two???

Thanks in advance for any help people can provide. I've tried to be as descriptive as possible above, but if anything needs clarifying or you need further details just ask. Thanks.

More about : psu blowing

a b ) Power supply
February 28, 2011 11:54:22 AM

sounds like youve got a short in the case somewhere. Rebuild the unit from scratch and try again. This time check to see if you've the motherboard touching the case where it shouldnt be. NB ensure that you DONT have any insulating washers connecting the motherboard to the case, there is a reason why there are metal contacts where the screw placements are.
February 28, 2011 12:44:17 PM

I'll give that a go, thanks. When the new unit arrives....

If anybody else has any other ideas/advice please let me know. Thanks.
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a c 275 ) Power supply
February 28, 2011 4:43:25 PM

Don't plug the new psu into the same wall outlet or any outlets on the same circuit.
I would have an electrician or someone like an experienced contractor look at that circuit.
It's clearly overloaded,thus the tripping at the breaker on the main service panel.
For heaven's sake DO NOT plug your gear into that faulty circuit.
Test your new psu far far away like in an outlet on the otherside of the house.
Where outlets are not on circuits with clothes/dishwashers/refrigerators etc that draw heavy loads.
February 28, 2011 5:33:11 PM

Thanks for that. Noticed when it blew the last time that the guy who did our bathroom put the underfloor heating on the same circuit as our front room. Which is odd as there are spare circuits available. Although that was over a year ago. I'll test the next one in a different room. Not sure what I can do if that is the problem as it's a media centre machine.

Thanks for your input.
a c 275 ) Power supply
February 28, 2011 7:28:52 PM

socngill said:
Thanks for that. Noticed when it blew the last time that the guy who did our bathroom put the underfloor heating on the same circuit as our front room. Which is odd as there are spare circuits available. Although that was over a year ago. I'll test the next one in a different room. Not sure what I can do if that is the problem as it's a media centre machine.

Thanks for your input.

That practice is illegal in Canada for most applications, i'm a certified and licensed heating contractor. Heating equipment is generally connected on it's own circuit(not to be shared).
It however does depend on the wattage and/or btu's etc.
If it's an issue i'd have a qualified person run a dedicated line(single circuit) from the main panel to an outlet for your AV/PC gear or the heating equipment.
Whichever is easiest.
Btw i also install dishwashers and guess what?
I run a single line of 12/2 AWG on a 15A breaker from the main board.
That's how we do it in Canada.
It costs very little btw to do it right the first time.
March 12, 2011 4:49:25 PM

Got a new antec psu which arrived today. Rebuilt machine from scratch, flicked the switch and the two fans moved slightly and then nothing. This was the case in both machines. The light on the mobo OS on to show current is flowing but nothing happens. I fear the mobo has died a death :( 

I may take it into the office monday and test it on my machine there, but I fear it will work.
a b ) Power supply
March 12, 2011 4:57:04 PM

possible that the old psu toasted something in the pc
March 12, 2011 5:00:51 PM

obsidian86 said:
possible that the old psu toasted something in the pc

That's what I thought. But if its toasted both machines my guess would be the mobo's, unless the symptoms suggest the processor or memory?
March 12, 2011 6:50:23 PM

What kind of fuse do your home use

Do you mean in the fusebox? Main fuse shows 100A and the others 32A, 16A and 6A. Not sure which fuse the room upstairs but It's had a pc running up there in past.
a b ) Power supply
March 12, 2011 7:30:29 PM

My guess is that you have taken out something on the MB which has created a short circuit.

first invest 20 bucks in a DVM (Can normally pick one up at a auto parts store - Radio shack overpriced) google "how to use a digital multimeter" OR SAVE TIME

With MB on table (GPU removed), ohms check all power connectors (20/24 pin and 4/8 pin ata Power. Connect the black meter lead to a ground (or a pin that a black wire would have plugged in to) and measure all pins that a "Colored (normally pwr) wire would plug into. Or see link for pinout.
If no shorts, then plug in the GPU and memory and repeat measurements on the 20/24 pin connector., If still OK then ohms check the power connector on the GPU 9The PCI-e pwr).

On the heater power - Illegal or not, it's a bad Idea. In this case, it is a question of if the wiring can handle it, some times "laws" are passed to safegaurd the 1 in 100 possibilities. almost like warning "Coffee is HOT". Reason for Bad idea is that when it clicks on a surge current is generated which will drop the voltage on that line, some what like a brown-out. In my house when I plug the vacumn cleaner in and turn on, I use to see my bedroom lights dim. Old House and I'd like to shoot the electrical guy!!

Also I would invest in a UPS.
A 2nd thing you could do is get a power strip, normally they are fused around 15 amps, get one that you can change the fuse and put in a slow blow 5 Amp fuse.

March 12, 2011 7:35:59 PM

Well i seem to have sussed it. It isn't the mobo, its the hard drive. Plugged the non OS hdd in instead and BIOS loads up. Which us great except I think the knackered drives all the photos we've taken to date of our 8 month old son :( . Ilk get a SATA external caddy just in case.

Thanks for everybody's input, got there in the end.
March 12, 2011 7:52:01 PM

I noticed when taking out the mobo that the screws had no washers, the old one did so put it back together with the rubber washers

I'll look into the electric as suggested. If there's a problem, it needs fixing!