PC power-on troubles

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Tom Del Rosso 14 years ago

The PSU and mobo are a couple of years old, but previously tested good. They've been in storage, and I just put them in a new case.

5v standby is good. Power switch works and is in the right place. But when I close the power switch, the power-on pin (of the ATX power connector) stays high (4.4v).

The 5v standby line is 5v disconnected and 4.4v plugged in. That sounds like too much of a load.

Hey! The fans just spun for an instant when I wasn't even touching it.

Now the fans spin for a second when I press power.

Maybe something is loose or shorted.

Will try without the video card and other connectors (like reset) disconnected.

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Ian Field 14 years ago

By the sound of that, I'd download the user manual and re-check all the front panel connectors.

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mike 14 years ago

good idea. Check the voltage on the switch pin when you press the switch.

The switch typically goes through a huge "glue chip" before reaching the power on pin on the psu.

If you figger it out, post the result. I've got a mobo with the same problem. The switch wire goes under a smt chip and can't be probed further. In my case, forcing the psu to turn on doesn't help.

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Ken 14 years ago

My experience under the conditions you describe would indicate the power supply is failing. It could also be the MB, but the failing item is most often capacitors that have lost some of the capacitance. If you have a ESR meter, check the caps. My guess is you will find some bad ones that are preventing the power from coming up fast enough.

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Winston 14 years ago

Also connect your POST board and look up the codes (for YOUR BIOS) that the MB tosses at you.

formatting link

--Winston

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Franc Zabkar 14 years ago

On Fri, 2 Dec 2011 12:32:07 -0500, "Tom Del Rosso" put finger to keyboard and composed:

Sounds like a short on one of the outputs. Should be easy enough to locate with a multimeter.

- Franc Zabkar

Please remove one 'i' from my address when replying by email.

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Jim Yanik 14 years ago

"Ian Field" wrote in news:Gg8Cq.64832$ snipped-for-privacy@newsfe18.ams:

I had a PC that would beep and not start up;replacing the CPU fan fixed it. the old CPU fan still ran,but apparently drew too much current. I only noticed it when I left the fan disconnected while checking other things,and the PC started right up. a new fan from Skycraft,and no more problem.

Jim Yanik jyanik at localnet dot com

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Jeff Urban 14 years ago

Skycraft in Florida ? Or are there more ?

Go figure, I go to Florida and think of Skycraft as a hot tourist spot !

Anyway what I would like to know is if the fan will run if the processor is bad. I got two dead boards here, on one the fans run and on the other they don't. On the one on which they don't the PS has been tested by substitution and continuity to the power switch has been confirmed.

J

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Tom Del Rosso 14 years ago

In this case, it's the caps in the PSU.

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Bob_Villa 14 years ago

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nd

I'm intrigued...seriously! Thanks, I may have had one like that and never thought of the possibility!

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PC power-on troubles

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