PowerMac G4 MDD (FW800) will NOT boot...possible PSU????

Question

Hi - just bought a used Dual 1.42 MDD with FW800....replaced the heatsink, RAM, hard drive, and DVD drive and was trying to boot it to load 10.5. I can not get it to boot or display any video beofre going to the fail-safe fan rush.
I searched the forum and read several posts concerning MDDs not being able to boot.....so I have performed some of the recommended troubleshooting steps - no avail. So here is my situation and the facts:
This is what happens when you power up the unit:
1. Both fans power up.
2. Red light on the motherboard lights
3. DVD (brand new) does an initial spin with the light coming on for about 8-10 seconds
4. Then fans go into overdrive with a loud, continuous roar
5. No video out
6. Seems the hard drives do not power up.
Here's what I have done so far:
1. Reset the PMU several times and different recommended techniques
2. Removed the battery, probably needs replacing...but should boot w/out it...right?
3. Swapped bootable drives...checked jumpers...still no power going to drives
4. The CAPS LOCK light on the Apple keyboard will not come on...so possibly the USB ports are not getting power
5. reseated the video card as well as all the RAM modules
I will test the PSU based on the recommendations from other posts - but was curious, based on the above facts, can it be safely determined that the PSU is bad (no CAPS LOCK light and no power to hard drives).
Any other ideas or suggestions....thanks.
jc

Answer 1

I agree with Japamac, it's odd that the HDs aren't spinning up. I bet they are but you can't hear them over the fans. The best it to use tester on them. Another thought it to unplug the fans, and startup the MDD with the case open -- be sure you ground yourself. You'll probably hear the HD 'click' when they startup; otherwise, if you touch the top (non-circuit board side) you can usually hear them vibrate.
Even if the HDs weren't getting any power, I'm not sure that would cause the wicked fans. One thing you can try is to disconnect the data cables to the HDs (and the power too), and see if the Mac will boot without the roaring fans. If possibile try booting from the Installer CD -- hold down the mouse button at startup to open the tray. You may need to boot again to actually boot from the CD/DVD. Completely dead HDs on the data buses can cause your Macs to have fits -- if they're not getting any power they'll appear dead.
I will not say with authority that it's not the PSU, but it may not. I've experienced what you described twice -- all issues with CPU board.
1. I bought for about $10 a condition-unknown 1.42 GHz dual card (low risk, high reward). At startup I get the bong, mb lights, no video signal, and the roar of the fans. The card gives roaring fans on both my 133MHz and 167MHz boards, which I know both work.
2. When I tried to undo an unsuccessul 133MHz to 167MHz motherboard FSB overclock. I didn't stir my conductive paint well, and I suspect the CPUs were clocked differently or overclocked way too high. I got the roaring fans at startup in this unstable situation with my bad paint job on the bus-multipliers (on the CPU board) and motherboard.
Without tinkering with the motherboard. I then put my other known working 1.25GHz dual CPU board, and I started up without issue. So something seemed out of what with the work on the bus-multipliers. I confirmed that when removed all the paint, put the other CPU board back in (the one that caused roaring fans with my bad painting) and I started without issue.
I've since gotten better with conductive paint, and the motherboard is back to 133Mhz and that old CPU is clocked properly (and since replaced).