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I have an early 2009 Mac Pro (2 x 2.66 GHz Quad Core) that recently started having issues. It started as the black screen issue, that I troubleshooted to find that there was an issue with the CPU tray. I found this out by doing the usual troubleshooting, replacing the graphics card and then buying a used second machine and interchanging the CPU cards between chassis.

I ended up replacing the 2009 Octocore CPU tray with an Early 2009 2.8GHz Quad core tray, as this machine has now become a spare machine, but the fans are cranking loudly.

When I run hardware diagnostics I see that the PS, Exhaust and Intake fans are not running and the PCI and Boosta fans are running at 850 rpm - seemingly not too far above min spec.

I would love to get guidance as to how to get the three fans running again and got my lovely mac pro back to its usual quiet self. The loud noise is unbearable in my home office.

Thanks for the guidance.

Wellardmac
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  • So, the fans are running top speed but they're not being reported as running? The boosters generally run at 1800-2500 at a reasonable idle (fast but still quiet). The larger case fans tend to top out around 3000, which is like living near an airport ;) Nominally, I'd expect boosters at 2k, case fans at 1k, which is essentially 'silent'. I'd suspect a sensor if it was one fan misbehaving, but 3 or more… I think you have a motherboard issue (which I'm not qualified to diagnose further, I'm afraid). Maybe have a look at iStat Menus who I think do a freetrial. – Tetsujin Dec 12 '20 at 16:41
  • They're showing as zero on the mac fan control app. What do you mean by motherboard? The spine? I already changed the CPU tray. – Wellardmac Dec 12 '20 at 16:50
  • I think you have too many sensors not reporting for it to really be a sensor issue per se. I don't know precisely what they all report back to, but that would be my suspect. Data is being sent, but not received. – Tetsujin Dec 12 '20 at 16:52
  • This only started as we were troubleshooting the black screen issue. It was silent before, but initiated after many reboots PRAM and NVRAM resets. Prior to that the machine was silent . – Wellardmac Dec 12 '20 at 16:54
  • You changed hardware - did you reset SMC? Shut down, unplug mains, wait 15s, press power button 5s, release button, plug back to mains, wait 10s, boot. (This is a kind of 'composite' reset, which definitely works on all Mac Pros) … Ohhh… & change the "CMOS" battery. CR2032 coin battery, maybe a quid/buck/euro from any supermarket ( or pence on eBay if you buy a lot) – Tetsujin Dec 12 '20 at 16:59
  • I did do the SMC reset after each step. – Wellardmac Dec 12 '20 at 17:17
  • It's between the lowest & 2nd PCI slot on the motherboard - https://d3nevzfk7ii3be.cloudfront.net/igi/NNA6D6x5dEcGGUvt.huge – Tetsujin Dec 12 '20 at 17:30
  • Just replaced it. That didn't work either. :( – Wellardmac Dec 12 '20 at 17:32
  • Then we're back to "I think you have a motherboard issue", which is where my expertise ends, I'm afraid. As you have two, I'd be tempted to build up from the other one & see what happens. – Tetsujin Dec 12 '20 at 17:39
  • Thanks for trying. That's how I figured out that the CPU tray was defective last time. I fixed that machine and gave it back to my daughter. I was hoping to have this working as a spare, but it's not viable to have the fans cranking all the time, much as the machine is otherwise functional. – Wellardmac Dec 12 '20 at 17:58

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After some research I discovered that the fans were blowing because I put a single CPU tray into a machine that originally had a dual CPU tray. Apparently it doesn't like this mismatch and runs the fans full, as it thinks it has suffered failure of a CPU.

Wellardmac
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