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PSU went bang


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#1 SWo2008

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Posted 19 December 2008 - 01:05 AM

Hi

I have a dell dimension 9100. From first purchase, it was always unreliable. Sometimes it would switch on. At other times it wouldn't. When I started reading about potential problems, the nearest similar problem which others were experiencing was a short in a USB socket. (I briefly spoke to a dell engineer - who thought that the problem sounded like a faulty psu problem). I tried as best I could to investigate all the USB ports. I couldn't find anything obvious. When I looked into the firewire port I found what could have been a culprit. I straightened the pins and for a while the machine seemed to become more reliable. It switched on regularly without 'misfiring' for about 2 months. Then the problems came back. I messed around with the firewire port and eventually it seemed okay again for about a week. Then the problems started again. This time, there was a 'bang' in the psu and the fuse was blown in the mains lead. I put in another mains lead and the same thing happened. So I figure the psu is (one of) the problems.

So I am about to get a new psu for the machine. But I have a couple of questions that I wondered if someone here could offer some advice.

i) Could it be that the mobo is already fried? I'd be grateful if someone could tell me how I could check. There's nothing obviously blown from looking at the mobo.

ii) I have a worry that I put in the new psu, but there is still a short somewhere else in the system so when I switch on, this new psu immediately goes bang! Is this a possibility? If so, is there any way to try and find that short before connecting the new psu.

Many thanks for any advice and help.

Simon

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#2 dpunisher

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Posted 19 December 2008 - 03:58 AM

As long as you are not buying/using a garbage PSU, then you should be OK. A good PSU will have built in short protection and shut down (without damage) if something is shorted.

Most motherboard shorts I have run across have been from blown rectifiers/mosfets etc. and even then they are more likely to go "open" vs "short". I have run across other components like hard drives and optical drives that shorted out as well. Sometimes you can get lucky and see charred components, sometimes not.

If you want to do a postmortem on the current fried PSU, first look at the components (vregs and mosfets) attached to the internal heatsinks. You can often see a scorch mark, or sometimes a chunk blown out of the component as well. Be careful poking around in a PSU as those big caps tend to hold a charge for awhile and can zap you.

Edited by dpunisher, 19 December 2008 - 04:03 AM.

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#3 dc3

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Posted 19 December 2008 - 04:08 AM

Usually if you hear an explosion it's one of the large electrolytic capacitors.

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#4 SWo2008

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Posted 19 December 2008 - 10:28 AM

Many thanks

Simon




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