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Need help diagnosing powerless computer

By brinkjr
Jun 30, 2006
  1. My computer went dark when I was using it. It seemed like a power supply problem, so I swapped out the power supply with a known power supply. Still dead. Double checked the power supply and they both work. Check the power switch on the front for continuity and the switch is good. The system has been rock solid for the past 1.5 years (ASUSP4P 8000 mobo). It's been months since I was in the case. It's in my basement where it is cool and I have a temp guage showing normal temps.

    My question is what do I investigate next? I do not have a spare mobo.

    Any help would be appreciated...
     
  2. iss

    iss TechSpot Chancellor Posts: 1,994

    What do you mean by "went dark"? do you mean it powered off and now wont come on? is the mobo receiving power? ( there should be a green light on the Mobo if the mobo is receiving power.)

    you could try stripping the components off except the CPU then power on, shut down add ram, power on. shut down, etc adding components to see if it will post. ( make sure you UNLUG the Computer each time and hold the power button in to drain any residual power from the system before you remove anything and before you add each part.
     
  3. an0nym0us

    an0nym0us TS Rookie Posts: 31

    what he said is our normal operating procedure at work. that's what i'd do.
     
  4. Tedster

    Tedster Techspot old timer..... Posts: 6,000   +15

  5. Dan_Sarandon

    Dan_Sarandon TS Rookie

    Note: Prior to considering the procedure outlined below please try resetting the CMOS RAM (i.e. BIOS’ settings) via the ‘jumper’ provided for that purpose – I am aware of three instances (two involving HP Vectras and a third involving a Nanosys system) wherein the ‘CMOS’ had somehow become corrupt such that startup via the ‘power button’ cycled the system on then immediately off after which it had no effect pending reset of the PSU (via disconnection from the mains) – In each case hardware reset of the CMOS RAM proved remedial.
    //////////

    Ok! I know it’s become ‘vogue’ to view the system board as a ‘black box’ – A stance I tend to concur with where the failed unit is a soldered on, near microscopic, and/or proprietary SMD --- However power conditioning (and other ‘manageable’ discrete generic components) are quite another matter! :)

    Shorted or ‘electrically leaky’ electrolytic and tantalum capacitors are a common cause of the following symptoms: No power-up or very brief power-up (On time < 2 Sec with the necessity of resetting the PSU prior to subsequent attempts)

    Shorted caps may be readily located using a multimeter (low resistance scale) and, in the case of electrolytics, as noted by Tedster, often by mere visual inspection.

    Quality electrolytic and tantalum caps are both inexpensive (typically less than $10 USD -- often much less) and readily available (one of many retailers being Jameco Electronics www.jameco.com) inasmuch as said caps are relatively large thru-hole devices replacement requires only modest soldering skills. And is a H___ of a lot less expensive than a new system board!!! -- But please observe the following caveats.

    -Prior to commencing work please remove the CPU and all bus cards (That the range of Murphy’ s Law might be constrained ;))

    -The replacement capacitor’s working and surge voltage ratings must meet or exceed the replaced unit.
    -Observation of correct polarity is critical!!!
    -The replacement's capacitance must at least equal that of the replaced cap (but may exceed same by no more than 10%)
    -The replacement’s tolerance & temp coefficient should be equal to or ‘narrower’ than that of the replaced component.

    -When handling the system board great care is required to avoid mechanical damage to the copious, minute SMDs figuratively peppering the board.

    -Desoldering the failed cap requires both care and patience as said component is often attached to the board with RTV or similar elastic adhesive – Care must be exercised to avoid thermal delamination of the board.

    Good luck!!! :)
    Very best regards
    Dan S.
     
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