Anyone with a 2012 21.5" iMac able to do me a favour?

Discussion in 'iMac' started by maximage77, Jan 6, 2019.

  1. maximage77, Jan 6, 2019
    Last edited: Jan 6, 2019

    maximage77 macrumors newbie

    Nov 4, 2014
    Quick back story, used to be an Apple Tech about 15 years ago in a previous career, no longer in IT though, so hand me a spudger, a torx and some kapton tape and I'm still quite at home, however not 100% up to date with the intricacies of more current machines.

    My parents iMac was slowing down due to being a 2.5" spinner, so offered to whack in an SSD, also upgraded the RAM while in there. All back together and I'm getting the dreaded fans spinning at full speed and the system is limiting the processor speed right down, so it appears and behaves as if the processor is maxed out (when in reality it is barely doing anything.)
    Screen Shot 2019-01-06 at 21.51.20.png

    Running Apple Hardware Test, it reports back with a fault of 4SNS/1/C0000008: TA0p--124 which indicates that the ambient thermal sensor has either coincidentally failed (this is usually referring to the one on the back of the LCD panel itself) or I managed to mangle the cable somehow. Have been Googling for a couple of days and can find barely any people with 2012 iMacs getting this error, lots for other years though, where the hardware is unfortunately different.

    However, if I run TG-Pro, (and this is where I start to come undone), it shows all sensors OK apart from GPU Diode having an N/A next to it. Now from what I can tell, this app should only show sensors relevant to that model machine, so this concerns me.
    Screen Shot 2019-01-06 at 21.50.38.png

    Additionally, running iStat shows no figure against the Ambient Logic Board, CPU Proximity, GPU Die, GPU Proximity, Platform Controller Hub and Power Supply Heatsink. Now in this instance, I believe all these are sensors this machine doesn't have as iStat doesn't always remove unnecessary ones from the list. However, general consensus online is that the Ambient Sensor (that Apple Hardware Test reports as faulty) is one that is attached to the back of the LCD, and iStat shows a temp reading for the LCD, guessing this may be the same sensor.
    Screen Shot 2019-01-06 at 22.42.12.png

    Sooo, what I'm hoping is that someone with one of these machines might also have these apps and be able to check and see if those are blank on their machines too? Mostly worried about the GPU Diode one on TG-Pro as I don't believe that should be blank.

    I have pulled the machine apart again and checked every single cable is plugged in. What I am down to is that it is either the ribbon cable running from the back of the display to the motherboard, as this carries the Ambient Sensors data or the Ambient Sensor itself has failed, neither of which is too major. There is also a small interconnect board on the back of the screen that joins the sensor and the cable, and if it is that then I believe it may mean a full screen replacement. Or it may be something to do with the GPU sensor. Or a mix of both!!

    Huge thanks in advance to anyone who may be able to assist!!
  2. AnonMac50 macrumors 65816

    Mar 24, 2010
    It could be because of the SSD, Late 2009 and newer models have a sensor to check in hard drive temperatures. What you need to do is modify the connection or use an adapter (modifying the connection is easy and shouldn't take long). Your iMac fan issues will most likely be fixed once that happens.

    EDIT: I just wanted to add, the reason this happens is that the computer cannot read the temperature on the SSD, and thus spins the fans up "just in case" it's hot. Or it just assumes it's hot. Ran into this on a late 2009 iMac and the fix was simply to modify the connection.
  3. maximage77 thread starter macrumors newbie

    Nov 4, 2014
    Thanks for trying to help Anon, much appreciated!

    Unfortunately in this case case that isn't the situation. The 2012 models didn't have that thermal sensor on the drive, so they can be run with a normal drive without having to buy a replacement sensor from the likes of OWC etc. That was one of the first things I checked before I started ordering parts.

    From OWC: "The Late 2009 – current iMacs will need the OWC In-Line Digital Thermal sensor with the exception of the 21.5″ 2012-Current iMacs!"

    Much appreciated anyway as Im still pulling my hair out a little trying to determine exactly what it is causing it.
  4. AnonMac50 macrumors 65816

    Mar 24, 2010
    No worries! Wish I could be of more help, but I don’t actually have any 2012 models (let alone with this issue). Hopefully someone else can provide more help! Please do keep us updated if you do figure it out! Good luck!
  5. Wickintime macrumors newbie

    Feb 27, 2018
    Probably not much help, but I have a late 2012 model 21inch and just a week ago I replaced the HDD with an SSD. I just cloned the drive to the SSD using CCC, took it all apart, dropped in the SSD and then spent some time cleaning the fan impeller which was covered in dust. I reassembled it, switched it on et-voila! I use DriveDX and it seems to track the temperature as it changes. I'm not aware of the fan being on at all.

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