View Full Version : PowerMac G5 has 4 CPU fans, and only 2 work!?

Sep 16, 2009, 11:14 PM
My CPU fans for proc.A are near-constantly capped at 300rpm(system minimum), no matter how damn fast the B-fans spin to compensate.

I have:
Kept it clean inside.
Kept CPU settings on Highest, as usual, but tried Reduced/Auto
Repaired permissions
Reset the PRAM
Reset the PMU
Booted into single-user mode
Reinstalled Leopard
Obtained & ran :apple:Service Diagnostic CD and passed all tests
Re-calibrated the CPU's only to notice the speeds now hover around 400rpm now...:confused:

What more can I possibly try? I don't believe a re-seating of CPU's is in order. They work great. All my fans & temperature sensors passed their diagnostics tests, too.
I am very irritated by the noise of 2/4 fans overcompensating and getting very loud, from 2000rm-4000rpm, and hey, my Mac is screwed up, and I really need to fix this.

It's the G5 in my sig. Mid-2004.
Thank you all for your brains, experience & consideration.

Sep 16, 2009, 11:18 PM
What amount of ram

What OS

What hard drive

need info.

Had the same machine. Make sure your hard drive isn't failing; this is sometimes difficult to diagnose on Powermac G5s for some reason.

Also make sure no dust inside the processor areas. Will cause fans to kick in because the dust retains heat.

More ram, faster hard drive on Highest -- and my same machine ran pretty quietly.

Sep 16, 2009, 11:35 PM
-4GB RAM (maximum)
-Nvidia 7800 GS AGP 256MB
-Two HDD clones, both Seagate, both are maintained well with DiskWarrior & TechTool Pro. No diff' on either drive. I'm 98% sure they are both good.
-OS 10.5.8

Thanks for your interest.

Sep 17, 2009, 12:59 AM
Well, whatever else you do you better change out those broken fans on the quick! Before something else breaks as a result of the heat.

Sep 17, 2009, 04:04 AM
It could be a flat back-up battery. That could affect the PMU settings. It's probably worth replacing it as a matter of course after 5 years, anyway.

Other than that, I'd suspect a deeper problem. By:

Re-calibrated the CPU's

I assume you mean thermal calibration using the service CD. Did it actually re-calibrate your system or did it just announce that everything was OK?

If it didn't actually re-calibrate the system, I would probably try removing and re-installing the 2 processors and swapping their positions to force a full re-calibration.

Sep 17, 2009, 04:17 AM
If you have your original PMG5 discs, I'd do a fresh install on a hard drive and bring it back to Leopard, too. Or try to boot off the oem discs and see what happens.

Sep 17, 2009, 08:55 AM
It could be a flat back-up battery.

Did it actually re-calibrate your system or did it just announce that everything was OK?

I will replace the battery today, and report back.
Yes, it did say that thermal calibration was successful, unless it lied, which for all I know, it may have...

California, I don't possess the discs no mo', but I do have a copy of my old G5's HW test, which this tower passed the day I brought it home, and again, yesterday.

Thank you all for the thoughts. Please, keep the smarts comin'!

Sep 17, 2009, 12:14 PM
It's not the fans since they are both CPU A. My CPU B fans are running slower than A on my G5 right now. At idle it would show 300RPM for the exhaust fans but temps were fine. I have been running it at max for the past 30 min (system load utility) and CPU A is sticking to 60 and B to 65. Those seem pretty similar to what I remember 2 years ago.

Also, Temperature monitor is reporting different temps than istat pro, so I don't trust it on the G5. istat shows 50 degrees when it is really 60/65.

I do seem to remember my CPU A always being the slower fan and that never made sense to me as I though the higher of the 2 should be running faster since heat rises. So it is weird that now CPU B is the slower one. That may have something to do with it being a 2.0Ghz CPU running at 1.8Ghz though. I also noticed the colour of the heatsink metal and pipes is different... maybe a more efficient material. However it is still running 5 degrees hotter, but still well within limits from what I understant. My Mac Pro hits 91 degrees for 2 of 4 cores in windows (die temp), but the fans don't rev up... and it stays at 3059Mhz and doesn't down clock to 2.93 or lower so it must be within limits.

Sep 17, 2009, 02:07 PM
Just a thought.

We're looking at the problem from the perspective of the CPU A fans running slow but there's an alternative explanation.

If the temperature control for the CPU B fans was the real culprit, then those fans would run too fast as a fail safe. With them running at full blast, there'd be enough throughput of air to keep CPU A nice and cool, so its fan control system would keep its fans at idle.

So maybe there's a sensor on the way out or a dodgy connection.

Sep 17, 2009, 02:32 PM
Interesting theory but FYI no air from the B fan goes through the A heatsink... or even touches it. I don't know why they made such an effort to split the air when it really wouldn't matter that much I don't think.

And 1700 is far far far from full blast.

Sep 17, 2009, 02:57 PM
You're right as far as the intake fans are concerned. I had one for 3 years, so I should have known that.

The exhaust fans aren't separated, though, and one fan at full blast will pull at least some air through both heat sinks.

Sep 17, 2009, 04:36 PM
Yes, the B fans are certainly not running at full blast, and adjust themselves often, so I assume they "work".
I just went out and blew a scarce $23 on a new PRAM battery, and nothing changed, except that my internet no longer works :( WTH?
I reset the PRAM again, safe booted, repaired permissions, reset PMU, and nothing. I reset PRAM a second time w/the new battery and that didn't solve anything...my 'net issue is still there. I'm typing on my lady's PC right now.

My istat pro widget has trustworthy looking temp. readings for bot the CPU's and their ambient sensors, so I can't say that they look guilty here.

I am so weary and beaten by this. Thank you all for your great suggestions, and please, keep 'em coming!

PS: Seriously, does anybody know why the battery swap reset my clock, and killed my internet connection? I put the old battery back and still no luck. Thanks.

Sep 17, 2009, 05:40 PM
PS: Seriously, does anybody know why the battery swap reset my clock, and killed my internet connection? I put the old battery back and still no luck. Thanks.

Because that little battery is all that is powering your G5 when you turn it off (or at least unplug it). The clock will lose time if you pull that out. For the internet, maybe some data is stored on whatever the battery powers, so you would have to re-setup your internet settings. What do you mean it doesn't work? Is it wireless? Ethernet? Dialup? Is it on a network? Did you ever have to enter a password? Is it a hidden wireless network? Does it use PPPOE instead of DCHP? Are any settings you had before still in the preferences or is it all erased? What message are you getting?

Sep 17, 2009, 05:45 PM
Well, the clock will reset, along with the other parameters stored in PRAM, when the battery is removed. It shouldn't affect your network connections, though. Do you connect via airport or ethernet?

Sep 17, 2009, 06:27 PM
I connect to cable 'net via ethernet. I'll call my uncle about that. He lives upstairs and runs the connection. If there's no easy fix, I'll just re-enter the network info w/his instructions.
EDIT: Just fixed the internet myself by manually copying settings from my Pismo.

Sep 18, 2009, 03:14 AM
I'm glad you got it back but I don't know what else to suggest. If it were me I'd be thinking seriously about re-seating all the components and interior cables (including the processors) and cleaning their connector blocks with a good electronic cleaning solvent.

Sep 18, 2009, 11:15 AM
If anybody wants to buy a tested, new battery, lithium ion 3.6v, please, feel free to make an offer! :D


Nov 2, 2009, 06:54 PM
Well, this thing is still way too loud. Does anybody have any comments on my current plan to change every fan, to new, quiet ones, especially those 2 on the PSU?
I'll probably have to remove a processor or both, to get at the PSU, which would be a good excuse to swap their positions for evening the heatload, and forcing a new recalibration.

I hate G5s! This is my fourth Mac, and because I'm flat broke, I always end up getting the Mac I can afford. :p