Mac Pro 5,1 diagnostic light on- won't boot

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Mac Pro 5,1 diagnostic light on- won't boot

I've had a 2012 Mac Pro A1289 3.33 GHz 6 core purchased refurb from Apple since 2014 that's been trouble free until now with the configuration it's had for most of it's years: 3 x 4 GB ram, a professionally flashed GTX 780, and 2 250GB Samsung 850 EVO's on an Apricorn Velocity Duox2 PCIe card in the second X4 slot from the top running OSX 10.11.6 and Windows 7 Pro.

Recently I took the PCI card out to put the SSD's into the normal HDD bays to re-install windows, once for Win10, then again after deciding to go back to Win7. After putting the PCI card back in the 2nd time the machine would not boot but only power on for less than a second then shut down (relay click heard), with a solid red LED diagnostic light at the upper LH corner of the backplane board near the front of the case labelled OVTEMP CPUA (the top most of 4 lights) that remains on. If I press the button labelled DIAG LED just below it I get a green light at the bottom of the same 4 LED's marked 5V STBY.

The machine was running fine only minutes before in both OS's when finishing up my OS install. Am wondering if I bumped or caused something while working only in the PCIe area. I did mis-seat the PCI card the second time and after re-seating it properly have since taken everything out and inspected for bent pins or anything loose or out of place. Still get the same symptoms after trying to boot with only the video card, normal and proven boot HDD, and wired Apple keyboard and mouse in place. Need some advice related to diagnosis, further testing, and fix.

Posted on Feb 1, 2018 1:26 AM

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Answer 1

Feb 2, 2018 7:21 AM in response to Little_Fish

I know it seems odd, but It is entirely possible that it is telling you the truth and your processor is reporting overheat -- essentially, failed processor chip.

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Answer 2

Little_Fish Author

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Feb 2, 2018 10:02 AM in response to Grant Bennet-Alder

Yes a failed processor does come to mind at this point (or perhaps a misreporting sensor). There's only one way to find out. Will report back when the issue has been determined.

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Answer 3

Feb 1, 2018 7:55 AM in response to Little_Fish

CPU A overheat certainly seem weird. Check for "wiggly northbridge heatsink". DO NOT remove processor heatsinks or anything else, just remove AC power, slide out the shelf, find the part and wiggle it.

http://www.xlr8yourmac.com/archives/jul14/071114.html

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Answer 4

Little_Fish Author

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Feb 1, 2018 3:35 PM in response to Grant Bennet-Alder

Performing an SMC reset didn't result in any change in behavior. Checking for "wiggly northbridge heatsink" is a long reach as I have a single CPU tray as pictured https://forums.macrumors.com/attachments/northbridge-sensor-lead-png.398551/

Using that diagram as reference I was able to reach in almost 3" from the left and it feels solid. I was also able to see the sensor lead and connector from the bottom and gave it a few taps for good measure. Everything in this area is very clean.

Would agree that a overheat LED is strange. I did find a 2010 tech manual online for reference but won't engage in any minimum configuration testing until I've heard back. I appreciate your response as can recall your name from when I purchased my first Mac's quite a number of years ago.

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Answer 5

Little_Fish Author

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20 points

Feb 1, 2018 7:10 PM in response to Grant Bennet-Alder

As an update, all behavior with respect to diagnostic lights is good when powering up minus the processor board (the entire tray). As soon as this tray is re-installed the issue comes back. Power on, immediate relay click followed by a 2nd click less than a second later and the solid red light.

Reference: http://tim.id.au/laptops/apple/macpro/macpro_mid2010.pdf page 34. Am now at flow chart on pg 39 but am reluctant to go to minimum config testing on the processor board.

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Answer 6

Feb 1, 2018 7:48 AM in response to Little_Fish

Perform an SMC reset by:

removing AC power cord.

press and hold the power-on button for a quarter minute to drain the power capacitors.

re-Install AC power cord.

attempt to start up normally.

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Mac Pro 5,1 diagnostic light on- won't boot

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