My hot Mac Pro! Sensors, fuzz, or what?

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Level 1

27 points

My hot Mac Pro! Sensors, fuzz, or what?

Mac Pro goes to sleep as it should, but at some point it shuts itself down. If the fans are spinning faster, or an external fan pushes more air through the box, it stays asleep.

Using iStat Menus app to show temps and fans' speeds and to boost fan speeds to test the result. Right now, iStat fan control is OFF, and a small desk fan blows air into the front of the case. Stays asleep, doesn't shut down.

Internal fan speeds are controlled by one or more sensors, right? If the sensors work, then the machine would be running fine and sleeping fine. Is the air path clogged, the sensors not working, or something else?

What needs to be fixed?

Specs: CPU: 2 x 2.8 GHz Quad-Core Intel Xeon; Graphics card: ATI Radeon HD 2600 XT 256 MB; Display: Cinema; Disks: 2 X 500GB internal, 2 TB FireWire external.

tia

OS X Yosemite (10.10.3), 20 GB RAM, 2 internal SATA drives

Posted on Jun 19, 2015 1:13 PM

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Answer 1

Best reply

Grant Bennet-Alder

Level 10

127,669 points

Jun 19, 2015 1:58 PM in response to harv47

what you described about sensors is right, but incomplete.

There are also two fail safe modes -- if a sensor stops working, or its results are out-of-range, the fans roar at full speed. If certain measured temperatures (such as the internal processor sensors) get dangerously high, your Mac will do an uncontrolled power-down.

The approved method for cleaning the inside of your Mac Pro 42b silver tower is to move it to place where dust is a 'don't care', then use compressed air to launch the dust bunnies airborne and out of your Mac. Don't use a household vacuum cleaner, as its plastic tools generate huge, electronics-killing static charges long before they generate a Zap you can feel.

There is no concern whatsoever that you will force dust into place where it can do damage or mess up connections. The spec for electrical connections inside your Mac is described by component engineers as a "gas-tight" connection.

A rare but vexing problem can be caused by the NorthBridge heatsink. It is mounted with two plastic pins. if one or both break, the northbridge chip get very hot and your Mac gets really flaky.

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Answer 2

harv47 Author

Level 1

27 points

Jun 19, 2015 4:11 PM in response to Grant Bennet-Alder

Re the Northbridge heatsink: I see four sensor readings for CPU (temps are F):

CPU-A Die 1 Offset: 142

CPU-A Die 2 Offset: 149

CPU-A Heatsink: 80

CPU-B Die 1 Offset: 140

CPU-B Die 2 Offset: 136

CPU-B Heatsink: 80

These readings are with the desktop fan blowing into the case.

I'll look at the reading again with the fan shut off. And buy a can

of compressed air.

Thanks, Grant!

Harv

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Answer 3

harv47 Author

Level 1

27 points

Jul 28, 2015 2:02 PM in response to Grant Bennet-Alder

Blowing compressed gas into the front of the case didn't seem to loosen any dust bunnies.

For good measure, I blew gas into the back of the case, to see if any dust collected on the

fans would come loose. Saw none. Also blew gas across the FBDIMM trays.

The machine stayed asleep as it should for a week. It then started to shut down overnight

as before. Blowing air into the case with a small desk fan didn't help.

To monitor and keep the FBDIMM riser temps down to double digits (80s and 90s F), I use

Bjango's iStat Menus' Medium fan setting, which run the fans around 1700-1800 RPM,

except the power supply fan, which stays around 600-650 RPM. The fans could run around

1000 RPM, but a custom setting disappears when the box shuts down.

Any suggestions welcome!

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Answer 4

The hatter

Level 9

60,990 points

Jul 28, 2015 2:29 PM in response to harv47

I found 900 rpm with SmcFanControl was all that was needed and new FBDIMMs did not need it - and talking 59-69*C (not 80-90F!) for proper functioning.

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Answer 5

harv47 Author

Level 1

27 points

Jul 30, 2015 3:10 PM in response to The hatter

Thanks, Hatter. Will try SMC fan control.

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Answer 6

harv47 Author

Level 1

27 points

Jul 30, 2015 3:45 PM in response to The hatter

How did you get SMCFanControl down to 900RPM? The defaults are all well above that. And "custom" settings use the default as a base. Am using 2.5.2. tia.

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