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Released on July 21, 2011. Core i5 or Core i7 Processor. Thunderbolt. This unit is also used to run the Mac mini Server configuration.

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no pwm in fan pin

I have a 2011 mac mini that has full speed fan all the time. I have checked the fan in other mac mini and it works correctly. I have checked pin 2 (near gnd in the fan connector) and it is always 3.3v, no pwm. I do not know which element generates that pwm for the fan, nor where is that component. I have tried to follow the track that goes out from the connector but i have found nothing. Anyone with the schemes may help me? please. it seems there are no missing components on the board. thank you

Update (05/26/2022)

Hello, i do not know if my smc chip is broken or not, what i know is that in the fan connector i have 12v in pin 1, tacho is measuring correctly in pin 2, pin 3 is always 3.3v and pin 4 is gnd. The problem is that the pwm that controls the speed of the fan is not existent, pin3 is always at 100% so 3.3V all the time. I do not know what chip generates the correct pwn to control the speed. I tried to follow the track that goes to the pwm but i got lost.

Does anybody have the electric circuit of the pwm? or tell me what chip is the smc? i cannot identify it in the motherboard.

I run the diagnostic and i got ( 4MOT /1/140000003: exhaust-6262) the number after Exhaust is the revolutions of the fan so that means nothing, it is maximum speed. There is no speed control because there is no pwn, just a 3.3v signal.

If could see the electric scheme maybe i can identify if it is the smc chip that is broken or maybe some capacitor or resistance.

Macfan software shows the speed of the fan and all the temperatures, everything is ok but the fan speed that has no control regulation.

thank you

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The error 4MOT /1/140000003: exhaust-6262 is telling us the signal is not getting through.

There is a feed back loop which controls the RPM based on SMC's temp sensor values and the tach feedback

The exhaust callout is telling us the feedback logic on the logic board has a problem from the fan and/or the fan speed controlling logic.

Sadly there are no schematics or board views from the mini's (at least I've never found them) The best I can offer you is to review the 2011 MacBook Pro schematics as the logic is basically the same. You'll still need to hunt down the components comparing things.

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Thank you so much. I have the schematics of several macbook but i do not think that they resemble the one in the mac mini, first of all they show 5v fan and the one in the mac mini is 12v, the rest of the circuit is not similar. i can follow the trace from the connector and i can see 2 resistors but they are not 47K; so far the only similitudes with the macbok schematics is the connector pins. I will keep searching.

thank you again

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It sounds like you have a SMC issue. What happens is SMC will ramp up the fan's speed as well as lower the CPU's clocking to prevent the system from damage.

I would see what the onboard diagnostic tells us. Restart your system and press the D key to enter, let us know what the error codes are.

Reference: Mac startup key combinations

Depending on the macOS release you have installed you might encounter it won't work, thank Apple from messing it up!

If that happens we need to see what TG Pro tells us the free version is a good start but the full version does offer some diagnostic functions. Take a snapshot of the apps main window, making sure to get all of the sensors and fan info into the snapshot and post it here for us to see Adding images to an existing question

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