On some of my G5 Powermacs I can see a strange behaviour of backside temperature (Northbridge).

Under MOS a G2/2,3GHz heats up over 70°C in a short time (eg. useing Webbrowser). Normaly I limit it with CpuFanControl to 55°C (on all my G5), but in that case, fan is blowing full, most of the time. Useing OSX on the same machine, Northbridge don't reach even 48°C under same conditions (Webbrowsing) by very low fan-speed. Its a late G5 with ROM 5.24f1. The same behaviour I can see also on a G5/2.0GHz with ROM 5.18f7.
My old (now gone) G5/2.3GHz, ROM 5.24f1 and a 1.8 GHz G5, ROM 5.15f0 does'nt do that. There temperature for Northbridge is always under 50° (MOS and OSX) at moderate fan-speed (can't really hear it)
All other temperatures (CPU, DriveBay......) are always normal.

What happens here?

OSX likely uses different naming for sensors. Backside is actually a memory controller, at least on the PCIe G5. If that one gets to 70C, you should likely rebuild your machine and replace the thermal paste on it. It’s a common cause of issues with the G5s.

>> On some of my G5 Powermacs I can see a strange
>> behaviour of backside temperature (Northbridge).

> OSX likely uses different naming for sensors. Backside
> is actually a memory controller, at least on the PCIe G5.

Isn't northbridge ⊃ memory controller?


Edit: corrected operator

[ Edited by Andreas_Wolf 08.09.2021 - 15:57 ]

Thank you for that hint - I'll renew thermal paste!

Quote:

Sometimes yes. Sometimes it is:
Northbridge = memory controller + PCIe (or AGP) graphics bridge.
I think, that Powermac G5 PCIe is the second case.

>> Isn't Northbridge = memory controller?

> Sometimes yes. Sometimes it is:
> Northbridge = memory controller + PCIe (or AGP) graphics bridge.
> I think, that Powermac G5 PCIe is the second case.

I'm well aware of the overall PowerMac11,2 system architecture. Seems my use of the '=' operator was kind of sloppy and thus has you confused with regard to my question. "Northbridge ⊃ memory controller" would have been the correct expression.
So my question still stands: Doesn't the northbridge chip (if present) always contain the memory controller, so the first implies the second? Or why is there the need to dinstinguish between those with regard to the temperature sensor?
(Btw, I don't think there were/are any northbridge chips that contain nothing but the memory controller.)

OK, I did a little bit of googling and yes, the Apple U4 (IBM CPC945) is a north bridge/memory controller unit. It also features PCIe support and additional stuff like I2C.

http://static6.arrow.com/aropdfconversion/86f55fc3c7ce0714ba0e1880ce7e6964ea1d4fa9/cpc945_ds_a15-6009-02.pdf

And here is nice diadram od G5 PCIe:

thehouseofmoth.com

I'd now renewed thermal paste on north bridge (backside temperature), but does'nt have any effect. Temperature always reaches 55°C and above, so that blower starts to be very noisy.
And again: It does'nt show that behaviour under OSX.

Apple Diagnostic says everything OK!
Could this be also influenced by firmware-version?

Edit: tested it again under MAC OSX: Temp never reaches more then 45°C (even looking YT (TenFourFox). Blower is always more or less ideling and never blowing like under MOS!

[ Editiert durch Amigaharry2 07.10.2021 - 13:03 ]

I can confirm this behaviour with my G5 at 2,7 Ghz.

MacOS seems to use some kind of CPUFreq thingie to lower the speed of the G5. There is no such thing on MorphOS and the CPU is always at 2,7 Ghz.

Temperatures on MorphOS : 86°C is indicated for the 1st CPU (and 77°C for the second CPU). I don't know if it is accurate or not but the temperature is maintained at 86° by the fans (I can hear them constantly, not very loud though). I get this temperature thanks to the temperature sbar. I don't know if there is a more accurate software to check them.

I installed MacOS X Leopard yesterday to see and, indeed, the temperature stays at 49-50°C when idle and jumps to 70°C on load (and fans start spinning louder).

In my case it's not the CPU-temperatures - these are OK (limited on 2GHz-G5 by setfancontrol (MOS) to 55°C) and they are'nt be noisy.
But the problem is the North-Bridge-Chip, which is located on the backside of the board. There are big cool-structures to cool it down. Air is blown through by a radial blower, located below the drivebay-fan, at backside of case. And this blower sounds most of the time like a starting jet!! AppleDiagnostics says "erveything is ok", Backsidetempsensor is ok.

The stange thing: I have 4 PowerMAC G5 here (2x2,3GHz, 2,0GHz and a 1,8GHz). Only one of the 2.3GHz and the 2.0Ghz shows that behaviour. The northbridge sots quickly over 55°C, which I've set as limit and the blower starts.........
In MacOSX they never get more than 45°C and the blower is ALWAY near idle-speed. So there must be something in MOS which puts much load on this chip.

Now to make it a bit stranger: Both other PowerMACs (2nd 2,3GHz and 1,8GHz) are running perfectly (MOS) at low noise - even under high power.

So, what is the difference??