Testing +5VSB on PSU to check whether PSU is defective

Discussion in 'Power Supplies' started by flexy, Dec 7, 2012.

  1. flexy

    flexy Diamond Member

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    I am having comp troubles and with my limited resources here I try to troubleshoot whether the problem is PSU or motherboard related.
    (Eg. mainboard doesn't start up right now)

    I have a ca. 6 year old "Thermaltake Toughpower 750W"

    When i jumper (paperclip "trick") the PSU PS_ON/GND (unplugged from board) then I can measure the rails, +3, +13, +15 etc. seem all be fine. PSU is also starting, fans spinning etc.

    I even can put a 5V bulb on the +5V line and its lighting up.

    Now to the +5VSB line (purple wire):

    When I do this "bulb test" on the +5VSB line, the light does NOT light up. I am getting the same problem as if i would plug in the PSU to the mobo, board is not powering up etc. and I can hear a very soft 50hz "ticking" inside the PSU.

    Questions:

    If i put the 5V bulb to the normal +5 rail on the PSU and it lights up, but does NOT on the +5VSB rail, can I assume that the problem is with the PSU?

    (Mind you that measuring the +5VSB rail with DMM otherwise tells me everything is allright, I measure 5V something on the DMM, however as mentioned I cannot drive the bulb from that voltage)
     
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  3. jolancer

    jolancer Senior member

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  4. flexy

    flexy Diamond Member

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    Solved...it was a bulged cap on my Toughpower PSU. Shame on TT because this was NOT a "cheap" PSU. I am not the first where those "SamXon" caps bulge out and fail, lucky it did NOT fry my board. I recapped it and everything is fine again - PLUS i saved $$$ on a motherboard which I was already about to get, mistakenly thinking the fault would be with the board.
     
  5. flexy

    flexy Diamond Member

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    Related Side-Note:

    Don't depend on measuring rails with a DMM only - a DMM can very well show all the right voltages, doesn't mean the PSU is ok.

    If you need to test a PSU you need a PSU load-tester!