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Dual 1.25 GHz Start Up Chime, Powers Up, then nothing

Message #1 - Posted 2006/01/13 - Mr. Newb

Here's my mystery:

The machine gets an every two months air blowing, so no smothering, no dust bunnies, no filth.

The machine gets a once a week video project (usually a TV show rendered to to DVD) without issue.

The machine worked fine, then one day it powered up with the start up chime, then just sat. The fans whirr, but that's it.

No flash to the optical Pro Apple Mouse - no USB apparently No hard drive chatter
No booting from start up CD
No video - monitor stays dark

So, by process of elimination, I swapped parts into other comparable and compatible Macs, all internal components via USB, IDE, and AGP ok in other machines. Compatible parts brought in from other machines had no change.

So it was either the Logic Board or the CPU.

I borrowed a CPU from friend: machine all good.

So I know the CPU is somehow flakey.

The mystery deepens:

So I let the machine just chill for a week, master power cable fitting unplugged from the logic board, PRAM battery pulled, and flakey CPU pulled out of the Logic Board.

A week passed, then I reinstalled the CPU and heatsink (yes, thermal grease) installed the power cable and battery and the machine started up and booted into OS 10.3.9!

However, with an eye on Temperature Monitor on the Menu Bar, the temp rose quite quickly at idle to about 56 degrees C. before I decided I better shut it down (the thermal cutoff for the 7455 is 62 degrees C)

I let it sit fully assembled for a half hour, started it up and I'm back to the crazy start up chime then nothing scenario.

Why would the CPU act wiggy all of a sudden on a machine with casual use?

Message #2 - Posted 2006/01/13 - Philip Ronan

Mr. Newb wrote:

However, with an eye on Temperature Monitor on the Menu Bar, the temp rose quite quickly at idle to about 56 degrees C. before I decided I better shut it down (the thermal cutoff for the 7455 is 62 degrees C)

Are you sure *all* the fans are running?

I had a similar problem with a G4 MDD machine. The power connector had worked loose on a small fan in a corner of the motherboard. The CPU kept running too hot and putting itself to sleep.

philronan [@] blueyonder [dot] co [dot] uk

Message #3 - Posted 2006/01/14 - Mr. Newb

Previously, Philip Ronan wrote:

Mr. Newb wrote:

However, with an eye on Temperature Monitor on the Menu Bar, the temp rose quite quickly at idle to about 56 degrees C. before I decided I better shut it down (the thermal cutoff for the 7455 is 62 degrees C)

Are you sure *all* the fans are running?

I had a similar problem with a G4 MDD machine. The power connector had worked loose on a small fan in a corner of the motherboard. The CPU kept running too hot and putting itself to sleep.

Yep- all fans breeze away... I was thinking something related to one CPU has a prob creating a thermal runaway.

After letting the machine sit for a couple weeks again, fully assembled, I did a CUDA switch reset, plugged in the AC cable and the same problem: the initial start up chime, then it sits.

Crazy - a bad CPU is supposed to signal five start up beeps - but then, maybe if one has a single processor and it's bad, one would get the five beeps. If you have a dual and one processor is bad, it's not capable of signaling the five beeps because there's still one processor inside that's ok...

Oh yeah, I forgot to mention: the red light on the logic board stays on and the power stays up and running, unlike some I've seen where the machine goes off the second they take their finger off the power button (which seems to indicate a P.S. prob)

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