MP 1,1-5,1 Mac Pro 5,1 Red Light On In Front of Fan

[Mattcooley2379]

Today I noticed may 2012 Mac Pro had a red light showing on the main board in front of the fan. The characters next to the light are R1531 to the left and OVTMP CPUB. I assume that it has something to do with on of my CPU's over-heating? Can anyone help me with determining what the issue is and how to fix it?

The Mac was still on and working but I didn't want to chance doing any damage to it if there was an overheating issue. I would very much appreciate all the help I can get. The only thing that has changed is I installed a new GPU (AMD Sapphire Nitro+ 580 last night) and everything booted up properly, even showing the new GPU in the About My Mac page.

I have not installed OCLP yet, but that was my plan, so that I can upgrade the OS to a newer OS. (Currently running High Sierra). I attached a pic of where I am seeing the red light (it's the second led cluster from the top above the PSU Fan cables).

 

[kimjongbill]

I don’t have my 4,1 in front of me, but I had a similar issue on mine, I don’t remember what LEDs were lit up. I fixed it with repasting the north bridge heatsink. There was a clip that fell off and I had to replace it. But then I had another similar episode and I had to replace the processor logic board with a new one, and that fixed it.

 

[MacCheetah3]

There was a clip that fell off and I had to replace it. But then I had another similar episode and I had to replace the processor logic board with a new one, and that fixed it.

Well, that doesn’t seem completely unheard of:

clip (snap rivet) for Northbridge heat-sink on 2009 Mac Pro 2X2.26

So I just picked up a Mac Pro on the weekend. I tested it prior to purchase with the ASD S3132 diagnostic. It passed everything EXCEPT the TNOD test, where it gave an error that the IOH sensor was above operating temp. Knowing this i purchased the unit at a reduced rate in hopes of fixing it...

forums.macrumors.com

As a further resource:

http://tim.id.au/laptops/apple/macpro/macpro_mid2010.pdf

Page 27 shows a Processor Board overview.

 

[kimjongbill]

Well, that doesn’t seem completely unheard of:

clip (snap rivet) for Northbridge heat-sink on 2009 Mac Pro 2X2.26

So I just picked up a Mac Pro on the weekend. I tested it prior to purchase with the ASD S3132 diagnostic. It passed everything EXCEPT the TNOD test, where it gave an error that the IOH sensor was above operating temp. Knowing this i purchased the unit at a reduced rate in hopes of fixing it...

forums.macrumors.com

As a further resource:

http://tim.id.au/laptops/apple/macpro/macpro_mid2010.pdf

Page 27 shows a Processor Board overview.

Yup, this was the thread I used to diagnose that problem. To diagnose the north bridge, just take off the heat sink and see if the north bridge heat sink is laying flat. While you're there, you might as well replace the rivet. Just make sure you have thermal paste on hand because you're gonna have to repaste both the north bridge and the processor (but you already know that)