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1.5 Core Solo, 1.66 or 1.83 Core Duo, or 1.83 or 2 GHz Core 2 Duo processor. This covers the first Intel-based Mac Mini models from Early 2006 to Mid 2007.

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How to lower the fan rpm below 1500

Hi,

As the fan of my old Mac Mini (Core 2 Duo, 1.83GHz, A1176) was annoyingly loud, I transplanted the mainboard into a new case and connected a 120mm PWM case fan. The problem is, that the system does not allow to set the fan speed below 1500 rpm, meaning that the fan always runs at its max speed. I already tried tools like smcFanControl and Macs Fan Control, but they also only allow settings between 1500 and 5500 rpm.

Does anyone know if it is possible to change the min rpm value in the SMC somehow?

Thank you.

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The fan you put in doesn't sound like its the correct part. It appears like the mini's SMC services doesn't know what to do so it goes into high RPM mode to make sure you're system doesn't over heat (which is a good thing!).

First I would get the correct part, Apple P/N: 922-7317 Fan. Hopefully the tach connections on the logic board for the fan are still working.

I would also download this app so you can see whats happening: Temperature Gauge (OS-X 10.6) or Temperature Gauge Pro (OS-X 10.8 or newer). Post a screen snapshot here for us to see.

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4 Comments:

Hello Dan,

Thanks for your response.

Actually I don't want to put in the same fan again, because it's a small fan and has to run at high rpms. My goal is to have a really quiet system.

The 120mm fan can run between 500 - 1500 rpms, and the rpm and temperature sensors are working fine (using Macs Fan Control). I can see how the rpm ramps up from lower rpm to approx. 1470. The issue is that the SMC does not allow to set a lower rpm than 1500.

Is there a way to change that minimum rpm value somehow?

Thanks

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Yes & No here. Yes it can when the tachometer circuit is present. Because SMC can't manage the RPM via the tachometer in the fan you installed you are manually over-riding it and as the software is unable to control things at the lower level you have a problem. This is not a workable solution. You need to re-install the correct fan and its likely the fan you did have in the system originally was bad which was the root issue on creating the noise that was bothering you.

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Not sure what you mean with "when the tachometer circuit is present".

The fan is providing the current speed to the SMC, but as it expects a minimum speed of 1500 it probably turns up the PWM to 100%.

So you think there is no way to modify the SMC's min fan speed?

Reinstalling the old fan is not an option, even at 1500 rpm my 120mm fan is very quiet, but it could run even slower and keep the system cool.

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Quick update that might be useful for others.

I installed Fan Control (http://www.lobotomo.com/products/FanCont...) which allowed me to lower the min fan speed to 1000 rpm.

First it appeared not to work and I uninstalled it again, rebooted as described in the uninstall instructions, and went back to using Macs Fan Control.

After the reboot and starting Macs Fan Control, the minimum speed remained set to 1000, and now the fan actually was set to that speed. Yay!!!

I can now freely change the speed between 1000 - 1500 rpm, or just leave in auto mode, and the SMC will slow the fan down to 1000 rpm as long as the CPU is cool enough.

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