Power Loss

Posted on 2010-01-07
Last Modified: 2013-12-11
Hi, thanks in advance.

One of our computers shut off during production.  It will not power up.  The fans spin and the lights come one for about 3 seconds then every thing dies.

Swapped the power supply with one that is known good.  Same symptoms (so it's not the power supply). Unplugged all peripherals, hard drives and everything except the power switch; same symptoms.  Removed the RAM from the board (now a bare board) same symptoms.  

Tested the P1 with my multimeter and there is no more then 1.2v coming through to the board.

Question:  Is the board scrap? Is there anything else I can test?
Question by:Bumslaw
    LVL 9

    Accepted Solution

    wow sounds like you have tested everything i would have done including checking on another machine.

    The only thing left to check is the processor - can you do a switch with another identical machine?  if you had a power surge then all sorts of components on the board could have died including the processor.

    Your only other check would be to remove all components from a "good" machine except the motherboard and install the faulty machines components.  this way you can determine that it is the motherboard.
    LVL 1

    Author Comment

    Thanks for the reply.  I don't think I'm going to go as far as swapping the Proc. (if i comes to that I will

    I will test the components from the bad machine, on my workstation, to see if any of them are dead.  

    LVL 69

    Expert Comment

    If the P1 connector is the 20-pin or 24-pin power connector to the motherboard, the power supply will not provide current until pins 13 and 14 are shorted (this normally happens when you push your case's power on button).  The voltage readings should be as follows:

    If the power supply doesn't provide enough current for startup, you could experience the same symptoms, so usually it's a good idea to try one from another similar machine.
    LVL 13

    Expert Comment

    by:William Fulks
    Sounds like your board died. Look at all the capacitors and see if any are leaking or puffed out at the top. They should all be flat on top. Here's an example of a blown capacitor:

    See how the one on the left is popped at the top? If you have any like that, you might as well trash the motherboard.
    LVL 91

    Expert Comment

    Here my troubleshooting procedure :
    Precautions :
    -During connecting or disconnecting devices, be sure to have the AC removed
    -Temporarily ground yourself, or use a wrist strap for ESD prevention

    -With a new motherboard : verify if all mounting standoffs correspond with the holes in the mobo !!
       Or test the motherboard outside the case, on a wooden  (non conductive) surface
    -Clean the system from dust, then  test with the minimum setup - disconnect also all peripherals and network cables :
    -What to connect :  only  motherboard + CPU + 1 ram stick, video card, power supply
    -Verify that the 4-, 6- or 8-pin CPU Aux power plug is connected
    -Verify that the VIDEO card has a power connecter - if yes, connect the power to it !
    Now power on  your PC : on boot, do you have a display?
    -if NO it is one of the connected: RAM, Power supply , video card or monitor, so if possible swap ram, Power supply, video card or monitor - leaving only motherboard and cpu
    -if YES, connect devices till the problem shows
    *** note : if the fans are running, this shows there is 12 V present from the Power Supply; this does not mean the PS is ok, you still need 3.3 V and +5 V as well; and other signals.
    Additional tests and things to try :
    -boot without ram, it should beep; (also, without video card)
    -try bios default settings, (if possible) or clear the bios by removing AC and bios battery
    -renew the CPU heatpaste, and verify that the heatsink is mounted flat on the CPU, allowing for a good thermal contact
    -you can also check the motherboard for bad capacitors as shown here :
    -you can test parts on another  PC

    The term POST refers to the Power On Self Test  procedure - here a link  with a short explanation

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