1 Reply Latest reply on Oct 8, 2010 2:48 PM by Doc_SilverCreek

    Motherboard Runs When A/C cord plugged in.

    zcomputerlab

      Sometimes I have an ATX or Mini-ATX board briefly start for 2-3 seconds but not power up and stay running after I plug cord into power supply.  If it stayed running, it has always been a board with a problem.

       

      A Dell board I bought with Intel chipset did this and did not post or display video.  The RMA replacement did the same thing.  The support tech blames it on power supply or RAM.  Both I always test with new parts.  Please fill me in why he is right.  He claimed the following but I strongly disagree:

      Hello

       

      Actually, that is normal for all boards, and TV’s etc, just about anything that uses remote power

      The first time it is plugged in, it may or may not come on

       

      If the reference voltage is slightly different, it will come on and stay on, until it is turned off

      If the system is not posting, and you cant turn it off, then you will have to unplug it

       

      TV’s will do the same thing, the first time you plug it in, the TV will come on

      Once you turn it off with the remote, it will go off and stay off, until the remote is used to turn it back on

       

      But the first time you plug it into the wall, it may come on

       

      Both boards were tested and fully working when they left here

      Something else on that end must be the problem

       

       

       

       

      Thank you,

      Steve

      Ascendtech, Inc.

        • 1. Re: Motherboard Runs When A/C cord plugged in.
          Doc_SilverCreek

          Well, I not sure his explanation is too clear, and it is definitely not true for all boards. It is a design issue with the board / product, but not necessary a problem.

           

          When you apply AC power , stand-by power is what comes on ( I assume this is what he means by remote power)

          The stand-by power operates a limited number of circuits on the mother board that deal with the power control and features that should work whether you system is on or off (like wake on lan, or PCI card wake)

           

          (SIDE NOTE: because stand-by power is present in many parts of the board when you system is "off" you should always unplug the power supply before attempting to install or remove any components. This is one place a lot of folks manage to kill their systems by plugging in stuff with the (stand-by) power connected)

           

          In the best hardware designs, the circuits should be configured so that everything stays off until told to power-on. However, many Hardware designer don't think about the possible race conditions on first power-up and fan jumps or on\off events can  occur.

           

          Many boards also have settings in BIOS set-up to define how the board is suppose to react to an AC power event. (Stay off, Turn on or Last State)

          Stay off and Turn On are self explanatory, but Last State means that if it was on when the AC was removed it should turn on when AC is reapplied.

          Some factories may just pull the plug when they finish building and testing so the first AC at the customer , the system powers on.

           

          With Intel high end boards ( I don't know desktops as well) you can press and hold the power button for 5 seconds to force a shutdown regardless if the Baseboard management controller is running or not.

           

          As far as the your problems,

          • Check the power and all the connectors. Some board require 3 or more connectors from the power supply. (The 2X4 pin - 12v to CPU is one commonly missed. which then causes the board to not POST, but the fans will run)

           

          • Check the CPU socket. CPU sockets pins are very fragile and dropping a CPU in off center can bend them

           

          • Make sure your memory is on the mother board's supported list and fully seated

          • Remove any add-in cards and see if system will POST without them if your having troubles.


           

          • Check all cables and wiring. Unplug anything not need to POST if your having troubles. Shorted USB plugs or Front panels missed wired can cause real headaches trying to debug.

           

          "Both boards were tested and fully working when they left here" would kind of worry me.  Why would a distrubutor open the ESD seal on a new board to test it and risk damaging it when it was tested by DELL before they got it, unless it was not a new board?