Bad Motherboard or CPU -How To Tell WHICH ???

Macintosh / G5 1.8 powerpc
May 2, 2011 at 11:32:55
Specs: XP, AMD

I have a basic PC that will not boot at all. The fans will spin...but that's it.

There are no beeps from the motherboard.

The monitor simply says "nothing attached....monitor is not attached to a computer"

I have removed ALL items (CD, HD, all cards, and memory)

It has an integrated video and audio.

With only a monitor, cpu, and power supply attached to the motherboard, I will turn it on.

The fans will spin...but NO beeps (none at all)...and no video output.

Is there any way to tell at this point WHICH is the problem....the CPU or the Motherboard ???

One other note: To turn it back OFF (so that the fans are not spinning)....I can hold down the power button for 4 seconds (or simply unplug it, of course).

Any advice appreciated....THANKS

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May 2, 2011 at 12:57:20
Try puting in one stick of ram. Sometimes that is needed to get a post beep. Also while your problem could be either your MB or CPU it could also be the PSU. Partial failure if you will is rather common. It doesn't take much amperage to spin the fans and normally if they spin this tells me the MB is ok. This is not 100% true I know but it has worked that way for me every single time. Before replacing the CPU I would see about borrowing a known working PSU or test the amperage ( not voltage ) of yours. Voltage can remain constant when there is an amperage drop. There is a certain amount of amperage required to power the CPU and spin the harddrive. I think it is somwhere in the area of 7 or 8 amps for the CPU versus something like .25 amp to spin a fan.


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May 3, 2011 at 14:33:22
Thanks. I will try another PSU before making any decisions about the cpu.

Does the fact that the 4-sec (button push) power-down feature is active/functioning indicate anything about the health of the motherboard?

(rather than the power cutting as soon as it is pressed)

I'm don't really know what enables that 4-second-button-press before power-off just assuming it is something withing the motherboard.


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