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Mac Pro 5,1 thermal shutdown problem

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Hi all


This should be  an interesting challenge for you guys.


I have a 2010 - ish Mac Pro 5,1. Its running either Snow Leopard for legacy compatibility or Mojave when I'm in a flashy mood.


I have a single processor tray which works fine for practical purposes but I also have a dual processor tray which is where the challenge arises. In order to get the dual processor tray to work, I have to put it in the freezer for half an hour before fitting it to 

the machine. If I do this it boots fine and runs for a good five minutes before the second processor (B) warms up, I get a red light on the tray and the machine shuts down.


If I try and start it without putting the tray in the freezer it fails to boot and the red light comes on. All the usual suspects have been tried, replacing thermal paste on heatsinks, replacing spring rivets on Southbridge chip heatsink etc etc. When the B processor is removed, the machine boots fine and the fans are noisy but can be slowed with software.


After much investigation it seems there is a fault/misalignment in the temperature value/voltage being reported by the hardware to the SMC device, which is (mis)detecting an overtemp and shutting the system down when it needn't.


The question for you guys is this. The SMC firmware is updated regularly and is accessible with software debugging tools (MacProSMCUpdate11.dmg). Can some clever person more up to speed (than me) with Mac firmware and software generally, point me in the right direction as to how I can:

                      a) locate the B processor temperature detection logic.

                      b) modify it so it either ignores the erroneous overtemp data or re-interprets it to give a correct (ish) value which                                does not cause a red light and a shut down.

                      c) install the tweaked software so as to avoid/evade the shut down issue?


That should keep you guys out of trouble for a few minutes at least, and stop you hanging round street corners and chewing gum.





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