Late 2009 Mac Mini Fan running at 7700 RPM. Fan was checked in store and they said it could be a logic board issue. I don't want to replace my logic board so is there any way of fixing the issue?

If your temps are OK but just high fan speeds perhaps a program like SMC fan control might work as it overrides the Mac settings.

Could also just be a bad temp sensor. Did they run a full diagnostic test on it...?

Run the Apple Extended Hardware Test, as per > Using Apple Hardware Test

Fan speed is a function of temperature in the system. There are utilities that report temperatures recorded by probes at various points throughout the system and the temperature recorded by these probes generally control fan speed. The one I use is Marcel Bresink's Hardware Monitoras it provides the most comprehensive set of information. There are others on the App Store but they are less comprehensive in the information provided. There are several possibilities for the high fan speed

1. some component in your mini is running hot -- too hot
2. a temperature probe is repporting false information
3. a temperature probe has become disconnected
4. the fan speed control chip has failed
5. the ventilation ports are clogged prventing proper airflow
6. your mini is in too close proximity to a heat source
7. your mini is enclosed so that it cannot get good air circulation and there is environmental heat buildup.

Items 6 and 7 you can check by observation and correct. Item 5 may require you to open the case and blow it out with canned air, but I would have thought the Genius at the store would have checked this. Items 1 through 4 are in all likelihood beyond your ability to fix and even if you did would cancel your warranty/Applecare. Internally the mini is pretty much a monolithic structure and best fixed by replacing the logic board. Trying to repair the logic board would cost many times more than a new logic board.

If it is running hot artificially slowing the fan speed will at best lead to premature system failure.

thermaltake mobil fan II: proctect you hardware and add life by keeping it coool.

I also have a late 2009 mini with a fan that comes on full blast as soon as the power cable is plugged in. Apple's diagnostics will tell you it's a bad fan, but given that it's happening before you even hit the power button, that's probably not the issue (I tested mine with a known-good fan, and it did the same thing). My best guess is that the chip that regulates the voltage going to fan is fried, so instead of a variable voltage the fan is getting a full-on 18VDC.

You can measure this by opening the mini, and putting a voltmeter across the black and grey wires on the fan connector--as you're looking at the rear of the mini, with the cover off, the fan connector is near the middle of the small circuit board that hangs at the rear of the optical drive. It's the 3-wire connector with black, blue, and grey wires.

Fan control software won't fix this, because (if I'm right) the chip that the software needs to control is fried. The only "right" way to fix this is with a new logic board. That's not acceptable to me, so I went online and bought a 5 Watt, 220 Ohm resistor, cut the black wire, and put the resistor inline. That drops the fan speed to ~2600 RPM, which is slow enough to be reasonably quiet but fast enough to keep the mini cool under most circumstances.

https://www.alliedelec.com/search/pr...x?SKU=70023234

Hi,

When the machine was powered on previously, the power button may have been held on for over 5 secs. On some models, this can enable the fans to keep running.

Do try : Intel-based Macs: Resetting the System Management Controller (SMC) for your model and see whether the fans stop after the reset.

If they don't, then do AHT: https://github.com/upekkha/AppleHardwareTest

Cheers

If the fan comes on full-blast when power is connected but the mini is turned off, download SMC Fan Control or some other monitoring software, and check the fan RPM. If it's over 5500 RPM, then you're almost certainly looking at a hardware failure, because the onboard controller--even with an improper PMU reset--will never push the fan faster than that (it's a 12VDC fan to begin with, so there's no way the controller would ever feed it 18VDC). My fan runs >7000 RPM, whenever the power cable is connected, and there's no way to slow it down via software, SMC reset, or anything. The inline resistor was the simplest and cheapest fix I could come up with. I've tested it at 100% CPU load in a normal indoor environment, and the CPU die temps stays ~65˚C, which is fine.

Actually, make that a 10-15 Watt resistor. The 5W gets a bit hot.