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Mac Pro PSU fan not spinning...

System: Mac Pro (early 2009)


After a while the system shuts itself down, and then repeatedly does so while trying to boot back up. After letting it sit a couple of hours, it boots back up, but again starts shutting itself down.

I opened it up and noticed the PSU fan was not spinning - which eventually caused the PSU to overheat and power off.


I ran a hardware test, and got the following error...

4MOT/1/40000002: PS-0


I searched on the Internet for this error, and it seems (I assume) that this error means the PSU fan is bad, but I plugged it into another fan port on the motherboard and it worked fine. I then, plugged one of the other fans into the PSU Fan port and it did not work.


I reset the SMC.

I reinstalled the OS (Snow Leopard)

I loaded "Fan Control" software (PSU Fan stays at 0 RPM and cannot be manually adjusted.)


At this point I'm guessing it's either the power supply itself (which I find hard to believe), or the PWM controller for the PSU Fan is not working. To get around the issue, I'm ordering a "simple" (2 wire for power only) fan to replace the built-in fan and a manual (knob) speed controller. (Total of $10, until the real issue can be determined.)


If anyone could help any further, I'd appreciate it.



===========


Wanted to add reason I didn't think it is the PSU...


Red LED flashes when power cord is plugged in and again when it's unplugged.

PSU PWROK LED is green

5V STBY LED is amber



Tags: Mac Pro, 2009, PSU, power supply, fan, PWM

Mac Pro, Mac OS X (10.6.8)

Posted on Oct 6, 2014 7:35 AM

Reply
6 replies

May 22, 2017 12:08 PM in response to tinojr

The other possibility is that the fan in the power supply has died. You can probably dis-assemble and get the information off the sticker on the fan. Unlike the custom fans everywhere else, that one IS likely to be a commodity, interchangeable part. Look up that part number.


My experience has been that they are only available new in the handy 10,000-pack in trays on pallets for factory use. But a quantity-one replacement with comparable size in mm hole-to-hole, air moved in cfm (or more), and noise generated in dB (or less) may be available for under US$20.

Oct 6, 2014 8:39 AM in response to Michael Tomlin

If that fan has a third yellow wire, it is an RPM output from the fan, and is read by SMC firmware and used in a feedback loop to control system temperatures.


The MOT failures are all MOTor failures, i.e., the fan MOTor is not spinning (no RPM output).


It is truly vexing to have something as trivial as this on a complex expensive component die on you.


These folks sell power supplies.


http://www.dvwarehouse.com/Mac-Pro-Power-Supply-c-4884.html

Or with some diligence, you may be able to find someone "parting out" a dead Mac Pro on eBay.

Oct 6, 2014 8:56 AM in response to Grant Bennet-Alder

The Apple fan has four wires and as I understand it the third wire is basically the tachometer and the fourth wire is used to control the speed of the fan.


I tested pins 0 (GND) and 1 (PWR+) on the motherboard and it is in fact feeding 12v power to the fan. I also tested pins 0 and 3 and getting 12v. Maybe I'm misunderstanding how it works, but the PWM voltage is used to "negate" the PWR+ voltage; this is how the fan speed is controlled, the higher the PWM, the lower the speed, i.e. no PWM means full speed.


It seems to me that whatever is supposed to tell the fan to spin, isn't or can't. Could there be a short on the backplane or do you still think it is a power supply problem?


Thanks for your input.


:-)

Oct 6, 2014 9:16 AM in response to Michael Tomlin

Most of the fans in the cabinet are under control of the SMC software. They do indeed run full speed with no software intervention, as a fail-safe mechanism. (Software crashes, fans roar at top speed.)


A program like "SMC fan control" can provide visibility to the temperatures, and SOME control of the base fan speeds. My recollection is that the PSU fans 'do their own thing' (unlike the main cabinet fans) and are not software controllable. Components inside the power supply determine the temperatures and adjust its own fan speeds.


If that is the case, when used in combination with your analysis above, you should be able to trace back to an output amplifier (intended to modulate fan speed) that is DEAD and stuck at an output that is telling the fan not to spin. I would hope a 29 cent component was responsible.


A short in the backplane seems exceedingly unlikely. Most of what the power supply does is directly onto its discrete wiring harness. The main DC harness to the motherboard uses high-current connectors. Using more than one of those for signaling or fan speed seems more wasteful than power supply designers could tolerate.

Mac Pro PSU fan not spinning...

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