Removing CPU from 1.8ghz DP PCIX G5 Power mac.

You model is a little newer than my 2003 unit, but you may have the same general configuration.

To remove a processor module on my unit, disconnect everything from the computer, remove the side panel and air deflector and lay the machine on its left side so that the processors are facing up.

Remove the front fan assembly. Using your fingers, gently remove the processor modesty caps by placing both index fingers under the edge of the cap on the "G" side of a cap (towards the front of the machine) and press in on the pair of latches on the under side of the cap. Then releast the second set of latches under the other end and left the cap off of the heatsink.

Then, using a long-shaft Philips screwdriver (#2 works fine, as I recall), remove four processor mounting screws from a processor and gently lift the processor module away from the logic board. Do not separate the heat sink from the processor chip.

Installation is pretty much the reverse.

Be very sure to mark the processors as to which position they came from, because if you put them back in the wrong slots, you will void thermal calibration and the fans will go into permanent firewall, unless you run the thermal calibration routine in Apple Service Diagnostic (version 2.5.8 is supposed to work on your machine).

⚠ The usual precautions about proper grounding and ESD protection should be observed meticulously.

There are illustrated instructions--plus some CAUTIONS⚠--on this iFixit site:

Processor and Cooling Unit

Be sure the model is the same. It's not blatantly clear to me which of the G5 variants they are using as a sacrificial goat.

Allan Jones wrote:

Be sure the model is the same. It's not blatantly clear to me which of the G5 variants they are using as a sacrificial goat.

Were I a betting man, I would put that iFixit demo unit as the 2.7 GHz LCS unit from early 2005, since it is obviously liquid-cooled and it is still using the half-AA PRAM battery in the PCI bay. Probably not at all like either of the dual processor 1.8's from 2004.

Yup, "This guide will review the repair process of an Apple PowerMac G5 model number A1047 EMC 2061 from 2004."

Rob wrote:

Thanks OCG, this is what i needed to hear! I just didn't want to dive into this without some prior guidance. My PM wont start up anymore, from looking at the crash log i've been led to believe that the 1st

CPU has failed. I'm going to try and swap them over to see if i can get this machine to boot again. I have DL the ASD dmg from the web so hopefully i can start bringing this back to life. I've seen a few replacement CPU / heatsinks available on bay too so i will be buying one of those if it is a simple CPU failure.

Thanks again for your detailed help.

The one thing I noticed in prowling around was that on some machines, the Philips screws are replaced by 2.5 mm Hex head screws (I'm not sure whether people were actually referring to allen heads or hex heads, since lots of folks don't know exactly what they are talking about).

Also, when you make the initial swap, you should try the ASD, which may show the failed CPU. In that event, until you get a replacement in, you can get by with disabling it in open firmware. Boot into OF with cmd-option-O-F keys held down, then enter the following commands:

reset-nvram <enter>

setenv boot-args cpus=1 <enter>

reset-all <enter>

That will keep the machine from using the second CPU in line.

When you get the other CPU replaced, you can repeat the above without the setenv line and be back to baseline.

Rob wrote:

Yes i have found out that mine does have the replaced screws so the philips driver is a no go 😟. Will have to source a new tool. I have found a very useful guide ;-) http://dl.dropbox.com/u/2189255/Powermac%20G5.pdf

On a side note, do you know what the other screw holes are for? These are located in the middle of each CPU unit where the cutouts are. One seems to be a tiny philips head and the other a larger philips which seems to be located through the CPU plate hole underneath the processor?

Not a clue as to what the other screws are for, though I would suspect something to do with securing the heat sink assembly.

Are the main screws actually hex head or are they Allen socket screws? 2.5 mm, which I have heard bandied about as the size of the head, is pretty small for a hex-head fastener; I have an Excelite set that I have used over the years in dealing with audio and video equipment and the smallest hex-driver it has is 3.0 mm. On the other hand, 2.5 mm is a common metric socket screw size, though there are not a lot of really long drivers available in that size. I think that I have a Bondhuis T-handle driver in that size that is fairly long, which I got to deal with part of my Dewalt thickness planer a couple of years ago.

The link is relevant to the first models of the G5, which is what I have.

Rob wrote:

My next plan is to remove the 2nd CPU, boot into OF and run the commands you posted. Will the G5 boot if i don't run the thermal calibration on the 1 swapped CPU? I know the fans will all go into over drive.

I think the only way to find out is to try it that way. My guess is that it will boot, but that is only a guess.

Does it boot into

Target mode...

http://support.apple.com/kb/HT1661

So you could use Firewire on another Mac to look at any logs?

Great to hear, thankls for the report. 🙂