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Interesting Bad Psu PSU starts but won't turn pc on

#1 User is offline   Rommel 

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Posted 05 February 2013 - 05:43 PM

Hi guys.

This is a first for me, perhaps not for you.

My buddies Dell Dimension 5150 wouldn't start so I took a look at it.

All it would do was flash a yellow LED once when the power button was pressed.
Unwired PSU and jumped it and it started.
Plugged into mobo connections only and again, only the yellow amber flash on start button.
Hooked my backup psu to mobo only and booted to keyboard failure.
Normal, no keyboard plugged in.
Back to his PSU, notta.
Back to mine.
Pc boots.

Never experienced a PSU that turned on jumping yet failed to turn on PC.
All connectors look good and are firm.

No I did not check for voltage and won't.
If it acts like this, it gets replaced.

Anyone here experience this before?
Just curious.

BTW,
Nice of Dell to make mobos that don't have the standard front I/O pins.
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#2 User is offline   waldojim 

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Posted 06 February 2013 - 12:20 AM

Your motherboard reads the voltages as your PSU attempts to power on, and sends back a "power ok" signal. If the voltage is incorrect, it won't start. But, that jumper bypasses that check. The motherboard actually protected itself from a bad power supply! Be happy! :D
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#3 User is offline   Rommel 

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Posted 06 February 2013 - 04:11 AM

View Postwaldojim, on 06 February 2013 - 12:20 AM, said:

Your motherboard reads the voltages as your PSU attempts to power on, and sends back a "power ok" signal. If the voltage is incorrect, it won't start. But, that jumper bypasses that check. The motherboard actually protected itself from a bad power supply! Be happy! :D



Thank you for the explaination.
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#4 User is offline   mjd420nova 

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Posted 06 February 2013 - 05:45 AM

Power supplies have a crowbar circuit to stop it from going to full power when it senses a short. Common, the fans give a jerk but won't turn when powered up. A short for sure. A close exam might reveal a bulged or leaking capacitor.
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