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Computer won't power on when auxillary power cable is connected

Discussion in 'Hardware' started by tg84569, Mar 21, 2008.

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  1. tg84569

    tg84569 Thread Starter

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    I have a ECS P4.945GCT-M/1333 (3.0) 775 mATX Motherboard and I installed Intel E2180 cpu and put memory stick on it. The computer won't boot - the cpu fan moved a second when I plugged in the power, and the stopped. If I disconnect the auxillary power cable, the CPU fan just can start, but of course it won't post. If I also disconnect the cpu fan, the power supply fan starts and I can see keyboard lights turned on for a second.

    I measured the power on auxillary cable and it is ok: 2 12v and 2 GND. I am pretty sure that the power supply is good: I put on another power supply there and it is the same thing.
     
  2. crjdriver

    crjdriver Moderator

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    Did you swap in a known good [ie working] power supply?
    What brand and wattage of power supply did you install?

    It would help if you posted your exact specs ie board, video card, brand and wattage of pw supply, etc.
     
  3. Rich-M

    Rich-M

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    I would bet a pin is loose from the heatsink/fan and it is so hard to tell when the board is screwed into case.
     
  4. crjdriver

    crjdriver Moderator

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    I went back and reread your first post. Do you mean the cpu fan started when you connected the atx power connector? If so, you either have a failed relay on the board OR you have a failed pw supply. Another possibility would be a pw switch that has failed closed. This is very easy to test; just pull the leads from the pw switch where they connect to the board.

    What pw supply did you swap in to test?
     
  5. tg84569

    tg84569 Thread Starter

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    The ATX power connector is always connected. And if the auxillary power connector is connected, when I plug in the power cable to the psu, the cpu fan moved a little bit and stopped. If I use the power switch on the case, it is the same thing. I even disconnected the front panel power switch connector to the motherboard and used a jumper to short the power pins on the board, same result. But if I disconnect the auxillary power connector, the cpu fan started.

    When the auxillary connector is disconnected, I measured the voltage from the psu on the auxillary cable, it is correct: two 12v and 2 GND. I am pretty sure the power supply is good. It is SPI 550w. The other power supply I used is the one came with my dell computer, only 200w, but it should be good too.

    What do you mean by "failed relay"?

    Not sure about "pw swich failed closed". How the pw switch works? When you press the switch, it should remain closed? And if you press again, should it disconnect the pins on the board?
     
  6. crjdriver

    crjdriver Moderator

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    OK, backup a little bit. Are you trying to either install a new board into a dell case or use a dell pw supply on a standard atx board?

    If so, you will have problems, the dell case, board, and until recently the pw supply are proprietary. That is you cannot install a standard board into a dell case, use a standard atx power supply on a dell board, or use a dell pw supply on a standard board. In short dell and standard atx do not mix or play well together.

    The pw switch is a momentary connection, it supplies pw to a relay which in turn applies pw to the system. If the switch is failed closed, pw is always on. If the relay or connection on the board has failed, it can always be on.

    FWIW I would suspect the board first since it is ecs, then the pw supply.
     
  7. tg84569

    tg84569 Thread Starter

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    I am only reusing my dell case, and everything else is non-proprietary. I can fit in the mATX board without a problem, the screws are on the right place. The only thing I am using from the dell case is the power switch.

    The pw supply goes to the motherboard with ATX and auxillary connectors. I am quite curious how the auxillary pw connnection could affect cpu fan - wish there is a diagram of the motherboard to see how it works. It used to work, and now it won't. I suspect the mb is the problem, but can not prove. For power supply, can I measure the voltage to see if there is anything wrong? The problem is I have to go through the mb for the pw supply start, isn't it?
     
  8. crjdriver

    crjdriver Moderator

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    You are asking for a problem using a dell case. Even though you think everything lines up, I can just about guaranty you that you will have problems. Dell cases are proprietary along with just about all of their hardware ie you cannot install a standard atx board and expect it to work.

    In short get a standard case and install your parts.

    You may or may not have a bad board however you will have problems using a dell case with a standard atx board.
     
  9. tg84569

    tg84569 Thread Starter

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    "The only thing I am using from the dell case is the power switch". In fact, I am not using the dell case at all and the barebone system just won't start.
     
  10. crjdriver

    crjdriver Moderator

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    If you have the board out of the case, then do not use a pw switch. Just jump the pw pins with a small screwdriver to start the board.
    There are step by step troubleshooting instructions at the top of the forum. It is labeled troubleshooting guide for problems builds. If you follow the guide, you will find the cause of your problem.
     
  11. tg84569

    tg84569 Thread Starter

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    I went to the store to exchanged a new board, and again it worked fine when I set it up. But when I put the motherboard, power supply and the dvd rom into the case and fastened the screws, it would not post again! Exact same symptom.

    This is unbelievable. Can the case cause any problem? It is a metal case with pre-drilled uplifted holes to mount the motherboard. At no time the mb would be touching the case, except the holes area.

    Since you mentioned that dell case might be a problem, could you explain what is the problem?
     
  12. Rich-M

    Rich-M

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    I haven't seen any of those cases with thew raised holes around for a while and was sort of wondering why? Perhaps that is the issue. Is it possible to put some very small flat risers in there that won't raise it up much and still mount the board properly. I mean I have seen some 1/8 inch off the base and perhaps less?
    Other thought is the psu. Dell psu could be proprietary and you have yet to tell us what psu you used. Also sounds like same ram i9n all these exercises and you need to match ram to motherboard specifically, not just speed of ram. Either Ram no being compatible or bad psu could cause these things to happen.
     
  13. crjdriver

    crjdriver Moderator

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    As I posted, you are asking for a problem using a dell case with a standard atx board. Just buy the correct case and be done with the problem.

    As before, dell cases are proprietary. You cannot install a standard atx board into a dell case and expect it to work. The dell case is made to dell's specs and it is NOT standard. As you have seen it causes a grounding/short problem. In addition even if you did get it to post, slots do not line up, etc. It just does not work.
     
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