PowerMac G5 11,2 only boots when logic board was reset

[netsrot39]

Hello,
I've been encountering some strange issues lately with one of my PowerMac G5s. I do have 3 G5s 11,2 but only one pretty much gets used regularly and behaves in that strange manner. The machine I'm talking about was rebuilt about 2 months ago and worked flawlessly until a week ago. Since then it basically refuses to boot. When I press the power button the computer seemingly starts but never chimes. After a short time it goes nuts and enters fans at full blast mode. Repeated power on tries yield the same results. The only thing that does indeed make a difference and grants a next boot is (while the machine is off but plugged) to open it, take the front fans out (I hope they're hot pluggable) and press the small "SMU reset button". Pressing the button on the logic board guarantees a proper start (this solution is replicable)

Initially I thought that my USB keyboard was preventing the PowerMac from starting up and unplugging everything from the system also brought it to boot successfully. I did a full check with Apple Service Diagnostics OF and no issues were found (trying to boot Apple Service Diagnostics OS does result in a Kernel Panic and in a LED7 checkstop for some weird reason). Once the machine has booted, it is rock solid (apart from waking up from sleep which exhibits the same symptom). So I now have a machine that will not sleep and that needs a quick and dirty fix in order to boot in the first place.

I also tried to swap the CR2032 battery but it was still pretty good (at 3.1V). Nevertheless I borrowed a CR2023 battery from a HP computer from 2014 because I do not have any CR2023 spares lying around. As far as I can tell it didn't make a difference and also the battery of the HP was at 3V so there should be no problems. Well, I'm still gonna try it with a brand new battery once I can get one.

My question is if anyone experienced the same issues with their PowerMac. Is there any good fix for this?

By the way, this post was written on the particular PowerMac.

Thanks for any hints you might have!

 

[netsrot39]

I've been using my other PowerMac G5 today but tried to power on the flaky one multiple times during the day and it worked every time! The only thing I had to do is keep the machine unplugged after shutting it down and the next boot was more or less guaranteed. So I have two choices: reset the logic board or unplug the machine after using it. The latter option is of course better since I do not have to open the machine and yank the fan out. Anyways, I'm glad to have this figured out (sort of) but weird behavior nevertheless.

By the way isn't it insane that the OG PRAM battery (which is now back in) still sits at 3V? (it has been almost 17 years!)

 

[Certificate of Excellence]

I've been using my other PowerMac G5 today but tried to power on the flaky one multiple times during the day and it worked every time! The only thing I had to do is keep the machine unplugged after shutting it down and the next boot was more or less guaranteed. So I have two choices: reset the logic board or unplug the machine after using it. The latter option is of course better since I do not have to open the machine and yank the fan out. Anyways, I'm glad to have this figured out (sort of) but weird behavior nevertheless.

By the way isn't it insane that the OG PRAM battery (which is now back in) still sits at 3V? (it has been almost 17 years!)

Yanno, I recall watching a video of a quicksilver that was acting absolutely bonkers (inconsistent boots, KPs etc and it ended up being a hard drive that was shorting) - op swapped the drive and sanity was returned. I'd start swapping points of wear like power cable, hdd etc. and see if that stops the weirdness.

Worst case scenario - you dont find the culrpit, and you could plug it into a power strip and velcro that to the top or side of your desk - cut the power from that strip vs having to bend over each time to unplug the actual cable from the wall.