Thread: problems understanding atx

  1. #1
    PC Fixer-Upper Waldo2k2's Avatar
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    problems understanding atx

    Ok,
    im at my service period in school right now and im having some trouble installing these new motherboards. they are microATX form factor gigabyte brand boards. We're using them to fix older systems that have the boards fried. I've just installed 3 that won't fire up, i've eliminated the possibilites of bad power supplies, bad power, etc. The fans will jerk, the "ram ok" LED stays lit, but the power led's don't come on and the system doesn't go. The pinouts for the power buttons are correct. I've gotten 2 other systems built exactly the same to fire up, but these wont'. I'm using a 300w Antec power supply, it worked fine on the other 2 boards, but these won't fire up. They can't be fried can they? otherwise the fans wouldn't even jerk and the "ram ok" led wouldn't be on. So, tell me, is it ok to use an ATX power supply with a microATX board? Do I HAVE to use a microATX power supply? From what I've read they're ony cheaper and have 1 fewer output modes than a normal ATX psu does. So am I wrong and I just got lucky with those other boards? Is there a jumper or fuse on the psu i have to mess with? Help!?
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  2. #2
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    try using the power supply in the boxes that work, to verify that they are ok, and try using the power supply in the working ones on the ones that don't work.

    Are you sure the CPU's are OK?

    Try those in the working boxes to verify.

  3. #3
    PC Fixer-Upper Waldo2k2's Avatar
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    I know the psu's im using are fine

    didn't think about the cpu's...I think im going to have the school invest in some testing equipment so I can diagnose mobo's and cpu's easier. I'll use that to check and see if the chip is ok.
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    Have you tried to toggle the power switch pins on the motherboard? I had an ATX board that I thought was dead too, but a simple toggle of the pins sprang the board to life. Worth a shot anyway?
    I haven't used a compiler in ages, so please be gentle as I try to reacclimate myself. :P

  5. #5
    verbose cat
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    I've built a few computers, and in a recent one I wired everything up, tried to fire it up and nothing happened. No HD spin noise, no display with an error message, nothing. I took the HD LED lead and reversed it (had green wire and white wire, changed so white wire is on what green was and vice versa) and hit the power button. Voila, 'puter worked flawlessly.

    Now, it is possible that I bumped or moved something else in my endeavor to do this, but I doubt it. I have had this in the past cause the LED's to not work, but never before this most recent board (an ASUS w/ VIA chipset, forget the exact model atm) did that reversal cause more than no HD LED function.

    It all comes down to the electronics I guess. Wierd stuff when you change the flow of one little electron path...

  6. #6
    PC Fixer-Upper Waldo2k2's Avatar
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    thanks jcat
    I'm an electrician so i understand what you mean
    Kind of annoying that something like that could kill the entire circuit, i'll give all the suggestions a try and hope for the best on monday.
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  7. #7
    Registered User Xei's Avatar
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    The motherboards may require a 12V, 4 pin, connector. Otherwise, I have no idea what your problem is. Faulty power switch? Did you check the voltages coming from the PSU with a multimeter? Are you using static mats and ESD straps? Your not trying to use CPU temp sensors under the CPU are you? Good luck, sir! The problem sounds quite solvable.
    Last edited by Xei; 10-26-2003 at 02:24 PM.
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  8. #8
    PC Fixer-Upper Waldo2k2's Avatar
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    FOUND THE PROBLEM!

    Turns out the psu's that were in thos computers originally not only fried the old motherboards, but they shorted out the hdd's too! So, no matter what PSU I used the system was drug down by those faulty drives (im thinking there was a surge one night causing those particular computers to blow their psu's). That's why the fan would just jerk. I discovered the problem today when I finally said WTF? after installing a microATX psu in one of them. So the first thing I did...unplug the HDD and there it went. So I put new hdd's in the system, and it fired up! I was sooooo excited that that was the only problem. So thanks to all that helped, you all got me to start back at square one and think things through again.
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