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PC not getting power -- testing PSU's w/ voltage tester

Discussion in 'Hardware' started by prokrastinet, Feb 10, 2005.

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  1. prokrastinet

    prokrastinet Thread Starter

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    I have a voltage tester that I picked up to test a lady's computer. She has an HP Pavilion 7955 I believe. Anyway, upon pressing the power button absolutely nothing happens. No fans or anything. Checking the inside of the case I see that even though nothing is turning on, the motherboard light is lit up, indicating that I am getting some kind of power.

    This is a P4 system, but there is only one 2x10, 20-pin ATX power connector on the HP power supply. The HP PSU doesn't have the 2x2, 4-pin 12V connector that I was told all P4 systems use. Thus, this HP is obviously proprietary. However, I tried connecting an Antec 300w (brand new) to the motherboard and again the mobo light lit up again, indicating power, but the system was still completely un-responsive.

    I don't know how to work my voltage tester. It has 5 Settings
    • OHM X1k
    • DC V (10 - 500)
    • AC V (50 - 500)
    • m A DC (25, 250)
    • BAttery

    I could never get any reads from either PSU when I didn't have the tester on OHM. However, both PSU's I tested got power through various connectors. Even when I tested the HP 20-Pin ATX connector it was getting power. Does this sound like a motherboard problem? Or despite getting power, the PSU is sending out the wrong voltages?

    Oh, and when I saw was "getting power", the bar wouuld read 0 OHMS as it did when I tested the battery in the voltage tester itself.
     
  2. Skivvywaver

    Skivvywaver

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    To test for power you need DC V. If you have the mutimeter on ohms and hit it with voltage it will most likely kill the multimeter.

    To test the PSU you would need to find an empty molex or unplug one from a drive. The black wire will be ground, orange is 3.3 volts, red is 5 volts, and yelllow is 12 volts.
     
  3. Arcadion

    Arcadion

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    The answer could be a lot simpler than this. Have you tried disconnecting the front power button and shorting the pins on the motherboard with a screwdriver instead? The power button could be faulty.

    Alternatively, keep a close eye on any fans in the computer as you plug in the power cable in the back of the powersupply, and again when you try to power the machine up. If you see the fans twitch (even just a little) but not start spinning, the motherboard is dead.
     
  4. Skivvywaver

    Skivvywaver

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    Might be as simple as the switch that turns the machine on is bad. HP uses one big plug instead of individual plugs. You would need to find out which two pins on the mobo start the machine and short them together with a screwdriver. If it starts that way it would be the switch. I am sorry, I misread your post at first.
     
  5. Skivvywaver

    Skivvywaver

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    Arcadion got it first. I was eating a piece of pizza and typing with one hand so I was very slow. ;)
     
  6. Arcadion

    Arcadion

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    Yeah, gotta watch that one-handed typing ;)
     
  7. Skivvywaver

    Skivvywaver

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    Gotta watch when having "Geek" supper. No sauce on the keyboard.
     
  8. prokrastinet

    prokrastinet Thread Starter

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    i checked HP's site also, about power issues, and they mentioned having the PSU set to 115v. The psu was set to something else, 200+. could that have cause the motherboard to fail?

    also, the power button has 6 wires coming from it, all connected to a seven prong connector to the motherboard (one prong missing purposely). However, im not sure yet which is power, ground etc. The colors go --black > red > black > yellow > blue/green > black.
     
  9. Arcadion

    Arcadion

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    I sincerely hope you know whether your country uses 115V or 230V for its mains AC power. America uses 115V, Australia/NZ/UK use 230V. If you have that switch set to the wrong one and power up your computer, at the very least your powersupply will be dead, if not the whole computer.
     
  10. prokrastinet

    prokrastinet Thread Starter

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    i didn't even think to look at the AC Power the power supply was using, because who would change it? That was how I received the computer, with problem above already in place.

    but if the powersupply was dead, would I still get the green light on the mobo telling me im getting power? and wouldn't there be a nasty burnt smell coming from the PSU? ive already done the sniff check ;) and its not burnt.
     
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