iMac G5 abruptly powers off when booting - but only on 10.5.8

[InAWhiteRoom]

Hi all,

So my new £10 iMac G5 is working a treat…with leopard 10.5. If I try to upgrade the OS to 10.5.8 (or 10.5.Sorbet), the initial boot works, but after restarting the computer, it chimes, I get a grey apple loading screen - and then an abrupt power off.

I’ve popped in a new PRAM battery, reset the PRAM, tried safe mode… I’ve even tried substituting some 10.5 .kext files relating to power management in 10.5.8. The only thing that resolves the problem is reloading the OS to stock 10.5 - which I fortunately have on DVD from my own original purchase way back when.

Anyone else come across this issue?

There’s chatter from when people on this forum were buying G5s new about them randomly shutting down, but they seem more concerned with faulty PMU/SMU hardware, rather than a software problem.

https://forums.macrumors.com/threads/imac-g5-switching-itself-off-randomly.197809/

 

[InAWhiteRoom]

So scratch that - it’s just powered down on booting from 10.5, too. It seems to work perfectly the first and second time it’s switched on, but subsequent restarts lead to this problem.

The capacitors look good. I’m going to try and decipher the LEDs on the logic board, that describe (I think) the status of the SMU.

What’s quite perplexing is that it happily stays on for hours in target disc mode, or once booted. It’s the startup that seems to cause problems. I’m wondering if my slightly janky M2-to-SATA adaptor SSD I have in place of the HDD might be having any effect here.

 

[TheShortTimer]

Anyone else come across this issue?

There’s chatter from when people on this forum were buying G5s new about them randomly shutting down, but they seem more concerned with faulty PMU/SMU hardware, rather than a software problem.

https://forums.macrumors.com/threads/imac-g5-switching-itself-off-randomly.197809/

I have an iMac G5 that shuts down randomly regardless of the macOS version - Panther, Tiger or Leopard. Very helpful souls looked over photos of the logic board and determined that many of its capacitors are shot.

The capacitors look good...

Ok but it's worth pointing out that the people who examined the logic board photos for my iMac G5 drew my attention to the fact that its capacitors also seemingly look good but under close scrutiny they are exposed as slightly swollen. There's a possibility that your machine might have the same issue. Going on my experience, I'd urge you to inspect the caps again.

 

[InAWhiteRoom]

I'd urge you to inspect the caps again.

You’re quite right - visible in the photo above, you can just see that one of the capacitors on the bottom right of the logic board is not like the others. Slightly swollen, with a central dark pinpoint spot. Oh dear.

Anyone fancy a recap job?

 

[TheShortTimer]

You’re quite right - visible in the photo above, you can just see that one of the capacitors on the bottom right of the logic board is not like the others. Slightly swollen, with a central dark pinpoint spot. Oh dear.

Don't despair... It wouldn't be difficult to pull and replace them. (Even if only one is afflicted, I'd remove the whole lot as a precautionary measure to save yourself having to go back in and deal with the others later when they fail.) I've bought capacitors for renewal/overhaul work on my 80s computers and they were cheap, plus the Mac only cost you a tenner anyway so it's hardly money pit territory.

The only reason that I decided against repairing mine was that I'd also need to replace its destroyed LCD and I didn't think it was worth it. Yours on the other hand is in much better condition.

Anyone fancy a recap job?

You could probably do this yourself with a suitable desoldering gun. I won't volunteer because I don't want to be blamed/excoriated if I botch something! Are you confident with soldering or would you be willing to learn? If so, think it over as it could be a fun project. If I was you with a machine in that condition, I'd consider tackling it.

 

[Certificate of Excellence]

On a side note, I cant help but just love the engineering, branding & design that went on inside these G5 era machines. Just gorgeous. Most imac owners at the time would never see it either. So cool

 

[InAWhiteRoom]

I agree - gorgeous