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Old iMac maintenance notes

by Poster Feb 9, 2023 7
By chance, I got a late 2013 21.5-inch iMac with a broken screen. After reinstalling MacOS, it can be used with an external monitor, but the fan is always running at full speed, making loud noises, and getting stuck seriously (iState information does not show that the sensor is overheated, but iMac automatically reduces the frequency to protect itself). Power on and press the D key to enter the detection mode, and get two error codes PFM006 (SMC fault) and VFD001 (Display fault). Multiple resets of SMC and NVRAM are ineffective. After a lot of research and experiments, we finally found a solution: 1. Install Macs Fan Control to manually control the fan speed. 2. Install [GoodbyeBigSlow.kext] (https://github.com/jakwings/GoodbyeBigSlow.kext) disable the BD PROCHOT thermal throttling Forcibly let the CPU 996 work. Although it treats the symptoms rather than the root cause, it solves the problems in use.

Replies

  • Anonymous9609 Feb 9, 2023
    There is a cable on the iMac motherboard connected to the back of the display screen (glued on), which is used to detect the temperature of the display screen and control the fan speed. If you don't connect this cable, the fan will always run at full speed, taking up computer resources, so the iMac will be very stuck and basically unusable
  • Anonymous9609 Feb 9, 2023
    I said wrong above. This cable is not on the motherboard, but comes with the display screen (upper middle of the back, next to the camera hole). https://i.imgur.com/AxVCPCb.jpg
  • Poster Feb 9, 2023
    @ Anonymous9609 Thank you, I guess this is the problem, but unfortunately the broken screen has been thrown away
  • Anonymous3690 Feb 9, 2023
    Alas, Apple is very good at this technology.
  • Anonymous9463 Feb 10, 2023
    The imac external screen is so visual. Can you post a photo?
  • Anonymous3692 Feb 10, 2023
    Trash guy, let's change to half-length mbp 2017
  • Anonymous9583 Feb 10, 2023
    The iMac 2015 2017 model should be a more cost-effective model, right? The 27-inch screen is really comfortable.