Resolved PowerMac G5 System Board Replacement

[defjam]

I have a 2.3GHz PowerMac G5 (7,3) which needs the system board replaced. I've got a replacement on the way and expect to be swapping it out over the weekend. I haven't cracked the case to see what will be involved so I'll be learning as I go. Before doing so I wanted to check with the forum to see if there is anything of note while going through this replacement. Things like gotchas, tips, tricks, techniques, etc. to making this go as smooth as possible.

Anyone have any experience with a system board replacement and know of any things of special note?

 

[AdiPlayZ]

I never do a logic board replacement on a G5 but here a note do not touch the processor pins on the logic board as well the processors itself. The G5 will refused to startup when the processors pins or logic board pins are bent. So be careful on the processors and the replacement logic board pins. Good luck on the replacement.

 

[defjam]

I never do a logic board replacement on a G5 but here a note do not touch the processor pins on the logic board as well the processors itself. The G5 will refused to startup when the processors pins or logic board pins are bent. So be careful on the processors and the replacement logic board pins. Good luck on the replacement.

Thank you for the words of caution. I replaced the system board yesterday afternoon and it wasn't too bad of a process. A few minor things to watch out for but overall not too difficult.

 

[AdiPlayZ]

Thank you for the words of caution. I replaced the system board yesterday afternoon and it wasn't too bad of a process. A few minor things to watch out for but overall not too difficult.

Your welcome

 

[micahgartman]

I've dissected too many G5s to count. I was known amongst my Mac Genius team as the go-to guy for PowerMacs and 12-inch PowerBooks. Here are some tips:

Replacing the main logic board may not fix the issue. The board and the processors/processor unit need to match. There are "B" and "Z" and "G" sets. The only way to figure out which one is which was to have access to Apple's PeopleSoft implementation (called GCRM) and see which parts could be ordered under that computer's serial number.

Removing the processors requires a VERY LONG screwdriver.

There are LOTS of sharp metal pieces inside that chassis—be careful not to cut yourself.

The "mid-plane" is a b¡tch to remove. Be patient and you'll figure it out.

Once it's all reassembled, you need to "calibrate" the processors. This requires a special piece of software. If you can't find it using the Google method, PM me and I will guide you to the source.

Good luck, and may The Force be with you.

 

[Eriamjh1138@DAN]

This may be useful.

Disassembling Power Mac G5 Motherboard

I will teach you how to replace the motherboard

www.ifixit.com

 

[defjam]

Thanks for all of the suggestions everyone. Unfortunately the new system board appears to be dead so I had to pull it and replace it with the original system board (the original system board has a bad DIMM socket). Pulling the system board isn't too difficult. The second pull took much less time than the initial one. The biggest issue I had were the two SATA wires and at the top, upper part of the board. They were difficult to push into the drive bays and didn't want to stay there.

Question: There's a very small plug wire which comes off the system board and goes near the (I assume) Bluetooth board. I was unable to find any connection point so I ended up leaving it disconnected. I took photos of the system for reference but must have missed this wire. Any ideas?

 

[defjam]

It turns out the system board I purchased was nonworking (when pressing the power button nothing happened, no lights, fans spinning, nothing). I swapped back in the original system board and the system now powers on. However it no longer boots to the desktop.

Symptoms: Press the power button and I hear the startup chime and the system attempts to boot. The gray boot screen with Apple logo appears and then the status "circle" starts to spin. Then the system hangs and the fans start to spin up (they don't appear to be full speed but definitely audible). Then it just hangs at this screen.

When starting up I can hold down the option key to get the boot selector and I can boot the Leopard DVD with the results being the same as above. I have reset the PRAM with no improvement. All the hardware in the system is the same hardware which was installed prior to the system board change. Thus it is all known to be functional (or was immediately up to the point I performed the system board swap). I have pulled the processors and inspected the pins on the system board and processor modules, all look fine. It appears these system cannot boot with just a single processor installed. I swapped the processor positions and that didn't change anything.

Any thoughts? Could this be related to the small connector and cable I mentioned earlier? Is it a temperature sensor?

 

[AphoticD]

Any thoughts? Could this be related to the small connector and cable I mentioned earlier? Is it a temperature sensor?

Can you post a photo of the connector and its location?

 

[defjam]

Can you post a photo of the connector and its location?

Here you go. This wire comes up on the memory slot side of the system board along with the AirPort Extreme and Bluetooth (I think the small board in the upper corner of the system board is the Bluetooth module) wires (this wire is not either one of those). It runs along the backside of the system board and terminates underneath a black paper cover near the lower portion of the I/O connectors (i.e. near the ethernet connector).

 

[AphoticD]

Here you go. This wire comes up on the memory slot side of the system board along with the AirPort Extreme and Bluetooth (I think the small board in the upper corner of the system board is the Bluetooth module) wires (this wire is not either one of those). It runs along the backside of the system board and terminates underneath a black paper cover near the lower portion of the I/O connectors (i.e. near the ethernet connector).



View attachment 884871 View attachment 884870
View attachment 884869

Nice work. That looks to be the modem filter cable which connects into the modem board, which is the small board on standoffs behind the speaker fan assembly. The cable pushes into the side of the modem board toward the front of the case, behind the thin black plastic shielding.

Unfortunately, I don’t believe this will have any impact on the booting of the Mac.

There are a few more resets, beyond resetting PRAM, which may help.

Try resetting the PMU - small button below the bottom Memory banks. See screenshot excerpt from the PowerMac G5 service guide.

If that does not help, try resetting NVRAM:
1. Boot into Open Firmware by holding cmd-opt-O-F at the chime.
2. At the prompt: reset-nvram
3. set-defaults
4. reset-all

If that fails to get the OS booting, I would try downloading, burning to CD, then booting from Apple Service Diagnostics (ASD) 2.5.8 and run the extensive hardware diagnostics to check RAM, logic board, CPUs, etc - only this version will work for your PowerMac, the later 2.6.3 is only suitable for the late 2005 model G5s.

 

[defjam]

Thank you for identifying the wire. I agree that it shouldn't have any effect on booting this system.

After trying the suggestions you've provided as well as downloading and burning the ASD 2.5.8 image I'm about ready to write this system off. It's not booting the ASD disc I created (CD, written on my Mac Pro running High Sierra) I'm just about done with it. I may try to burn it on my alternate G5 system and if that doesn't work I'll probably just throw in the towel. Spent too much time on it already.

 

[defjam]

Well, it's now working as before. Not sure what happened but I suspect maybe a connector wasn't well fastened. I decided to reseat the connector to the front fans, the IDE connector for the optical drive, the two wires next to it, and the wire next to the SATA cables but not the one which connects to the rear fans. I also pulled the "B" HD and it booted right up. Reinstalled the "B" drive and it boots right up. It must have been a poor connection on one of those five connectors. Anyway it's as it was before and I'm happy.

 

[AphoticD]

Well, it's now working as before. Not sure what happened but I suspect maybe a connector wasn't well fastened. I decided to reseat the connector to the front fans, the IDE connector for the optical drive, the two wires next to it, and the wire next to the SATA cables but not the one which connects to the rear fans. I also pulled the "B" HD and it booted right up. Reinstalled the "B" drive and it boots right up. It must have been a poor connection on one of those five connectors. Anyway it's as it was before and I'm happy.

Well done. That’s my kind of perseverance!

I have found myself scratching my head with my G5s like that a few times. They were complicated, hot running beasts with many parts.

In most cases, reseating RAM helps. This is likely due to RAM banks and/or modules failing from years of heat. I have witnessed RAM modules in my G5s simply fail, causing intermittent kernel panics.