24 iMac loud fans

[Danwilderspin]

Hi everyone,

I currently have a problem with my 24" iMac 8,1 . When I turn it on I get fan blowing full speed.
I then installed fan control and a sensors app and noticed that none of them even suggested I had a cpu temp and gpu heat sink sensor. They weren't there let alone registering.
I opened her up checking connections all were good.
I then rebooted and used Apple hardware test and got the 4sns TmOP error.
I am struggling to find anywhere what this means and how to fix it.
It also just randomly switches off even when fans are at high speed....

Help?

 

[Danwilderspin]

Hi All,

An updare on this - wasted more money and still stuck... so i put in a new logic board...and guess what.. same problem? when i run about 5 different temp gauge programs none show the od temp, cput temp or the hdd temp - despite all being plugged in? so i could have another logic board ssame problem (unlikely?) or its something else... helP!

 

[DeltaMac]

Try an SMC reset:
Shut your iMac off.
Unplug everything from the back, including the power cord.
Let it sit unplugged for at least 15 seconds.
(check the cooling inlet directly above the power cord connector. That sometimes will be completely blocked)
Plug the power cord back in, but wait another 10 seconds or so before pressing the power button.
Plug in ONLY the mouse and keyboard.
Press and release the power button. If your fans are now under control, you can plug in whatever else you usually use. I always like to do a PRAM reset at this point, too.
If none of this helps, carefully check ALL the sensor connectors, including the ones on the back-side of the logic board.
If you don't find anything else -
Maybe a faulty power supply….

 

[Danwilderspin]

Hi thanks for that but,

Not sure if i mentioned this but even with fans on full power *both boards) it will switch itself off randomly still. I assumed it was overheating so put on compound but made no diffenece. did an dmc and pram reset no dice.

Also again snot sure if i mentioned - i have used 3 different temp sensor programs and none of them even discover the odd, hdd or cpu sensors (i mean not even reporting 0128 or anything they ar just not there!) on both boards?

I then took the board out and put in my working 08 iMac... problem still happened.. so i am really stuck - could it be a bad cpu or wireless card? clutching at straws now

 

[DeltaMac]

When did you first start getting the constant fans?
Was it AFTER some hardware change?

You said that fan control software doesn't see the fans, or show any temps?
That SHOULD be a stuck SMC chip, and the SMC reset (simply removing all connections and power, and letting it sit for a few minutes) should fix that.
If no resets, or any other testing, do not help -

When you replaced the logic board, you swapped the video card from one logic board to the other, correct? The temp sensor for the video card may still be disconnected, or the sensor has failed.

Are you sure that the fail code is 4sns TmOP ?
That fail code doesn't appear in Apple's list of codes for that model iMac.
Can you run the hardware test again to verify that?

There's a single-wire sensor connection on the top edge of the power supply.
It's a tiny connector that can easily be missed, and the wire might be accidentally tucked underneath when you were putting all the cards, etc back in place.
If that is not connected, it's another reason the fans will run at full speed.
I DON'T know if that also means that the other sensors won't be detected properly (I never tried that)

Finally, after replacing some other parts, the power supply remains suspect, could just be a problem like a failing capacitor.

 

[Danwilderspin]

Ok psu is good as i swapped that too...

anyway...

***UPDATE***

I've fixed it (and am probably the first one too based on hours of searching the web)

The problem?

You wouldn't believe it ... a bad CPU!

I had an old 2.4 from and 07 iMac surprised it worked but thought id test it and it booted lovely fans normal and all temperatures were back!

Ever heard of that?

I am going to order a new correct cpu - it did have a 2.8 but will the 3.06 drop straight in as it was also offered at that spec?

Cheers all!