iMac CPU fan at full speed

[Ken Li]

Here is my situation and story. I am fixing an iMac A1225. After replacing the logic board. everything else seems working fine except the CPU fan is running at full speed. I tried everything but nothing worked.

Attachment is the report of all sensors & fans. It seems all sensors are normal but only CPU fan is running like crazy.

Anyone has any idea about it?

Thanks for helping me.

 

[Transeau]

Did you reconnect the LCD temp sensor?

 

[GGJstudios]

If all the hardware is connected and functioning properly, try resetting the SMC.

 

[chevalier433]

Here is my situation and story. I am fixing an iMac A1225. After replacing the logic board. everything else seems working fine except the CPU fan is running at full speed. I tried everything but nothing worked.

Attachment is the report of all sensors & fans. It seems all sensors are normal but only CPU fan is running like crazy.

Anyone has any idea about it?

Thanks for helping me.

run a hardware test

 

[AppleNewton]

reseat all cables, sounds like something is either not seated correctly or possibly bad logicboard connector. if you have access to ASD or AST you should be able to pinpoint the problem a bit better if reseating doesnt cure it.

 

[Ken Li]

Did you reconnect the LCD temp sensor?

As the report shows, all sensor were detected and the readings are normal. I have checked all cable connections times, but they seemed normal.

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run a hardware test

That's something I am not able to do. Because the iMac is running windows.

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If all the hardware is connected and functioning properly, try resetting the SMC.

Had tried 4-5 times. It doesn't work

 

[Transeau]

As the report shows, all sensor were detected and the readings are normal. I have checked all cable connections times, but they seemed normal.

The Mac EFI will no report that a sensor is present, when a sensor is not present. In other words, if the LCD sensor isn't attached, or the wire has been damaged, the system simply will not show that it exists.

That said, the only reason that the iMac would run one of it fans at 100% is when it is unable to detect and/or use one of the sensors tied to that fan.

 

[Ken Li]

The Mac EFI will no report that a sensor is present, when a sensor is not present. In other words, if the LCD sensor isn't attached, or the wire has been damaged, the system simply will not show that it exists.

That said, the only reason that the iMac would run one of it fans at 100% is when it is unable to detect and/or use one of the sensors tied to that fan.

Will try that. Thank you very much.

 

[hawaiitek]

Did you find a Conclusion? Figure out why the fan is running at full throttle?

Did you figure out what the problem was? Its got to be something simple.

I'm dealing with the same problem with my A1225.

The original logic board was dead. So I replaced it and the system booted, but CPU fan ran at full throttle after about 5-10 seconds after system turned on. Everything was plugged in fine. (CPU is not overheating)
Then, I replaced that logic board with another one. Same issue, cpu fan running at full throttle. WHAT IS THE DEAL?

UPDATE: Fixed it. Solved. It was the front panel sensor at the top of the IMAC next to the webcam. It was plugged in to the connector backwards, or it wasn't connected in all the way. I also replaced the thermal compound on the gpu. Running quiet as ever now.

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