24" 2008 iMac full fan issue...

[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....
***
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

 

[Lifeisabeach]

That error certainly suggests a hardware problem and likely the logic board. Since you already replaced the logic board, that seems much less likely, but there's always the off-chance that you got a lemon replacement. Have you ever done anything else with the hardware like replace the RAM?

 

[pm-r]

I guess you have tried doing a PRAM and SMC reset??

And if and when doing the SMC reset, keep holding the power button longer than suggested, and also leave it unpowered for maybe ten minutes or longer.

Intel-based Macs: Resetting the System Management Controller (SMC) - Apple Support

 

[chscag]

I then rebooted and used Apple hardware test and got the 4sns TmOP error.

That's a temperature sensor error. Any program which can read fan speeds and temps should indicate 3 separate readings for your iMac: CPU, Optical Drive, and Hard Drive. I'm not sure about your particular model iMac but it should have a temperature sensor attached to the hard drive. Additionally there are sensors for the CPU and Optical Drive. It's possible one of those sensors is bad. Since you replaced the logic board, I would suspect the sensor that attaches to the hard drive. However, it could very well be another sensor that's amiss.

 

[johnodd4]

I would say bad temp sensors indeed..

But also make sure you check your ram is correct for that model of machine faster ram can also cause the fan to come on full tilt.

 

[pm-r]

I would say bad temp sensors indeed..

But also make sure you check your ram is correct for that model of machine faster ram can also cause the fan to come on full tilt.

Where do you get the info that "...faster ram can also cause the fan to come on full tilt." from??

I can understand if the fan control wire is dislodged or damaged during a RAM upgrade, but adding faster RAM…. Hmmm…????

 

[Lifeisabeach]

Where do you get the info that "...faster ram can also cause the fan to come on full tilt." from??



I can understand if the fan control wire is dislodged or damaged during a RAM upgrade, but adding faster RAM…. Hmmm…????

If I'm not mistaken, bad RAM or RAM that is too fast for the logic board they are put in can in fact cause the CPU to work harder, leading to increased heat, leading to the fans ramping up. A little Googling seems to confirm that. This person, for example, had his fans ramp up after installing new RAM, and only resolved when he put the old ones back in:
http://www.likely-answer.com/26069085/New-Ram-Causes-Fans-To-Speed-Up-On-Wake-Up

Same thing here:
http://www.ehmac.ca/anything-mac/60140-g5-freezes-fans-ramp-up-scream-bad-ram.html

 

[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

 

[pm-r]

That's pretty bizarre that none of the temp sensors seem to be working, unless a gorilla or a goat worked on that iMac!!

That could only occur if:
- all the temperature sensor chips failed — almost infinitely impossible
- the cables are damaged - very likely
- the temp sensor connectors are not making contact properly - very and most likely.

- a gremlin inside - very unlikely and also the wrong time of year.

Have you got a good Mac tech handy to give you some help??

 

[johnodd4]

the only reason i mentioned the ram is on certain macintoshes mac mini's and some iMacs after installing ram that wasn't designed for the machine in question or cheap ram the machine indeed starts to accelerate the fans out of control which can damage the heat sensors.

 

[danwilderspin]

***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!

 

[Lifeisabeach]

***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?

Well since pm-r gave a definitive list of what the problems could be, I guess this falls under "gremlin"? ;D

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!

I didn't even know the CPU could be replaced alone in an iMac. If there are no differences in the logic board used, then yah, it should.

 

[pm-r]

WOW!!! What are the odds on that — no temp sensor readings with TWO different CPUs??

I guess I missed that possibility. Must be getting old and brain dead coming on…

 

[pm-r]

Well since pm-r gave a definitive list of what the problems could be, I guess this falls under "gremlin"? ;D

I didn't even know the CPU could be replaced alone in an iMac. If there are no differences in the logic board used, then yah, it should.

It seems that the OP's early 2008 iMac 8,1 uses a ZIF Socket for its CPU and is replaceable — albeit, a bit of a fiddly PITA to do but doable. If it's actually worth it or not would depend on a lot of things I guess…

Is it possible to upgrade the processor in the Aluminum iMac models? How are these processors mounted? @ EveryMac.com

Lookup Mac Specs By Serial Number, Order, Model & EMC Number, Model ID @ EveryMac.com