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Desktop won't start. Will boot by shorting ATX connector.

by Avranu / December 31, 2015 8:24 AM PST

I'm working on a dell precision 390. PC began exhibiting strange behavior, including memory and battery warnings. I replaced both. Now the PC won't turn on when the power button is pressed. The computer fails to respond at all; no display, fans, lights, etc.

I can short the green/black wires on the ATX connector (shown here: https://www.youtube.com/watch?v=nYb7UaWip8w) and it will boot and run normally. I understand this means the power supply still works, but I don't understand what it suggests is broken.

When the computer is on, the power button reliably turns the computer off... so the button appears to work fine. What could be causing this issue? Could it be a capacitor on the motherboard? Is there a way for me to test that?

Any pointers would be greatly appreciated!

Thank you!

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All Answers

Best Answer chosen by Avranu

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That's a clear sign the motherboard is gone.
by R. Proffitt Forum moderator / December 31, 2015 8:41 AM PST

The green wire test worked but the motherboard is not sending the signal from the motherboard PWR ON to the green wire.

I've seen new techs not want this to be the case but hey, they eventually get enough repair jobs and learn this.

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Answer
PS.
by R. Proffitt Forum moderator / December 31, 2015 8:42 AM PST

Forgot to mention that a voltage check of the CMOS battery is required too. Still means a motherboard issue here.

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Thanks!
by Avranu / December 31, 2015 9:52 AM PST
In reply to: PS.

Thank you! Yes, the computer was reporting low voltage on the 3v battery. I tested the old one (2.8v), and replaced it (new reads 3.2v)... both should be in range, but I still get the same warning on occasion.

So, you're saying this is definitely a motherboard issue. I appreciate having some resolution, at least! There won't be anything I can do to fix the problem, aside from replacing the motherboard, is that correct? I've seen suggestions about replacing the capacitors, but I'm not sure how that could possibly be helpful.

Thanks for your help!

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The circuit from PWR ON to the green wire
by R. Proffitt Forum moderator / December 31, 2015 10:18 AM PST
In reply to: Thanks!

Is on the motherboard. I've found some techs that want to fix that circuit but no schematics, etc mean it's unlikely. Yes it could be badly configured jumpers but still the motherboard. In fact I don't need a CPU for this test.

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