[johhhn]

Symptoms-
Fans turn on
No video
No Bong
HD powers up

Tried-
Replaced PRAM battery (also reset many times *properly*)
Unhooked HD
Swapped out RAM

Any ideas? Could it still be Power Supply?

[mountainash]

It could be the Power Supply. Or you could have a dead logic board. The hard drive and fans will spin up as long as there is power, but the power lines to the logic board are separate.

You could try booting it in to taget disk mode and accessing it from another Mac. This will tell you whether the logic board is working.

[johhhn]

I forgot to mention--

-1- time it did boot up, it bonged and booted up to the flashing System folder (hard disk was disconnected)-- this was after I tried resetting cuda several times,, but it hasn't done it since then

[mountainash]

Could be the PSU, could be the hard drive. Try a different hard drive, or disconnect the hard drive and try booting from CD/DVD.

[aquilles10]

I have the same problem with with a MDD 867 dual G4. It used to chime on start-up with now video and it would eventually go into full blare vaccum mode. I tried everything, from swapping RAM, to reseatting the CPU to resetting the PMU. Nothing worked. As a matter of fact, it stopped chimming after a while.

Just yesterday, I took it to the Apple Store to have it diagnosed in case I missed anything. The Genius narrowed it down to a dead cpu, a dead logic board, or a defective power supply. Considering that we would have power spikes once in awhile and I would have to reset the PMU every once in awhile, I think that power supply is shot. I sure wish I didn't give away the original load power supply to the Goodwill!

Any how, I hope this helps a bit.

[mountainash]

Originally Posted by aquilles10

The Genius narrowed it down to a dead cpu, a dead logic board, or a defective power supply.

"Genius" HAHAhahahaaaa....

[Waragainstsleep]

Narrowing this sort of thing down without swapping known good parts in is tricky without a Service Diagnostic CD. And one of those won't help much without a video signal.
Swapping/pulling RAM is a good one to try, simply trying to boot from CD will be worth trying if you haven't.
A spare AGP or better yet a PCI graphics card would be worth trying too.
Try disconnecting CD and HD drives for these tests where appropriate, (this is the minimal configuration approach- try booting with just PSU, CPU, logic, single RAM stick and graphics card. Disconnect everything non-essential) if you're really lucky maybe an IDE cable has failed.

[mountainash]

You could probably take it to an Apple service centre, and they can diagnose (for a fee), and then quote you a fix price.

If you want to do it yourself, then get another FW800 machine, and swap over the components one by one.

If the logic board is dead, it might not be worth fixing.