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Power supply (PSU) keeps blowing when switching on

By sordish
Oct 4, 2010
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  1. My PC has been working fine for a couple of years then all of a sudden yesterday the PSU failed. The fuse at the wall had blown so I replaced it and then plugged the 3pin kettle lead back into my PSU. Turned on the PSU and "Bang" a spark flew out the back of the PSU and so did a waft of smoke. Now its dead. I bought a new PSU and rewired the internals of the PC and double checked all wiring. Plugged it in switched on the PSU. Turned on the power button of the PC and "bang". The PSU emited a pop and smoke and again its dead. Could this be a motherboard problem. ? Please help. I'm about to order an new PSU but I fear it is doomed unless I change my strategy !
     
  2. Route44

    Route44 TechSpot Ambassador Posts: 12,172   +37

    When a PSU fails, especially in the manner in which you describe not only does the psus die but it can damage the motherboard, harddrives, etc. I would not buy a new PSU at this point until you can determine if the mobo is good.
     
  3. sordish

    sordish TS Rookie Topic Starter

    Thanks but the problem is I don't see how I can test the motherboard without buying a new PSU to power it up. I have ordered 3 cheap PSUs and am awaiting delivery. I intend to strip the board down so that no components are plugged in. I iwll then attached the two motherboard power connectors and switch on. If the PSU blows again then I know that the motherboard is very likely to be causing the problem and I will buy a new one. If all is well then I will switch off and plug in each components, CPU fan, Graphics, sound, HDD, cooling fans, one by one until I find which component is causing the issue.
     
  4. raybay

    raybay TS Evangelist Posts: 10,716   +6

    Typical of some power supply failures... Best to test with another power supply, and when it works, buy a new one. Don't risk your motherboard and other equipment with that one of many failures. One failure is enough.. If the test power supply fails, you know you have to replace the motherboard or track down the problem that is not worth the time and trouble to find.
     
  5. mike1959

    mike1959 TS Addict Posts: 1,126   +22

    PSU failures

    This sounds familiar. For a PSU to blow with an explosion, it must be drawing a great deal of current from somewhere. Look around under the motherboard for a loose screw or standoff that could be the cause of a short circuit. You can replace the fuse in the mains plug with a much lower value, to save your PC's PSU. You might try 5amp or even 3amp, you will blow those fuses, but it's a lot cheaper than new PSU's.
     
  6. raybay

    raybay TS Evangelist Posts: 10,716   +6

    It is the part. A major power supply brand had this happen with a large number of power supplies, and recalled them, replaced the part, and sold them as Refurbished. We bought a lot of these former $89.99 units for $31... nary a problem since they replaced the component.

    What is curious is that you would find it happening over and over...

    Don't see how it could be the motherboard. based on how motherboards work.
     
  7. mike1959

    mike1959 TS Addict Posts: 1,126   +22

    PSU failures

    Would think it's fair to say many cheaper PC power supplies are are built to 'just good enough' standard. The switch-mode design is supposed to shut down rather than destroy itself, but it happened to me also. It's worth checking the mains lead for any obvious faults, and buy a new one if any doubt.
     
  8. jobeard

    jobeard TS Ambassador Posts: 13,517   +336

    there's a short circuit to ground somewhere between the wall socket and whatever is attached.

    if the PSU is suspect, don't install it into the system but DO connect to the wall socket.
    if it's bad, it will self distruct and you have an issue with the provider.

    if it's ok, then install into the system. If it THEN fails, clearly the system is grounded internally (shorted)
     


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