Mac Pro 3,1 won't boot after suspected RAM riser failure

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Level 1

4 points

Mac Pro 3,1 won't boot after suspected RAM riser failure

My Mac Pro (3,1) has been my daily work from home driver and had an unexpected shutdown while I was having a break a few days ago. I came back to the computer thinking it had gone to sleep but it wouldn't wake, or boot properly. It powers on but doesn't chime or show any display.

I had a similar issue a few years back and found that one of the risers had a leaky cap which was preventing it from booting (but fans were full blast instead of off), so I looked at the remaining riser. I found that a bug or something must have got in and died on it and corroded a bunch of pins on DIMM1.

What I have tried:

Bought another riser and tried multiple different (good) RAM sticks in it
Put the riser into the empty slot below
Removed the GPU, tried another GPU known to work
Removed all drives
Remove power cable for 15s while holding the power button, and booting again
Removed Lithium battery, drained power to machine, tried a new battery
Cleaned the bad riser and tried it again

What happens every time with all of the above troubleshooting:

The machine powers on, but no fans run and it doesn't chime. The only fan that runs is the GPU. All LEDs on the riser light up, even if there's only one or two sticks in it, and when it's placed in each riser slots.

Diagnostic LEDS:

At one point when I ran it Both OT A and OT B were red, all other LEDS were off. This only happened once and I haven't been able to replicate. Now every time it runs I get the following diagnostics:

SLP: off
STBY: orange/yellow
ERRB: off
ERRA: off
OT B: off
OT A: off
GPU: green
PWRG: off
EFI: green

Any idea what is going on? Has it shorted and fried the main board or is there something else I can try?

Mac Pro

Posted on Feb 10, 2022 5:55 PM

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Answer 1

Best reply

Grant Bennet-Alder

Level 10

127,843 points

Feb 10, 2022 7:17 PM in response to jordan248

<< When I do this both OT A and OT B light up red even though the system is powered off >>

if I recall correctly, that is a good sign.

STBY lit when pressing the button says the "always-on" power supply that provides standby power is working. This is required for startup.

I don't have the service book for that model, but you may be able to find a link to one online.

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Answer 2

Feb 10, 2022 6:37 PM in response to jordan248

No chassis fans?

Check the PRAM backup battery for more than 3.0 Volts in hand. If low, replace it.

Non-recharging long-life Lithium coin cell half-hidden behind the graphic card slot. CR2032 used in car-key fobs and garage door opener controls is a good substitute.

If no joy, conventional wisdom is the strip the machine all drives and of everything in a slot and look for power light blinking a code or the chime. The chime is played under software control when it passes the Power-On Self Test and is all working. Then add back ONE item at a time.

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Answer 3

jordan248 Author

Level 1

4 points

Feb 10, 2022 6:48 PM in response to Grant Bennet-Alder

No fans at all apart from the GPU.

I checked the PRAM battery which was reading 3.01v, replaced it with a new one reading 3.2v and there were no changes.

All drives and PCI cards have been removed, the only thing I have put in is a known working GPU. I've tested two with the same results.

There's still no chime, and no power light even when it's running. Could the issue be the logic board? I thought since the EFI diagnostic light is green that it should be getting to the software control part right?

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Answer 4

Feb 10, 2022 6:56 PM in response to jordan248

Strip the machine and leave ALL the drives and cards Including the GPU card OUT for the duration of your testing, unless/until you get a chime or the blinking power light.

If you don't get a chime leave the memory risers OUT as well, and look for the blinking power light.

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Answer 5

jordan248 Author

Level 1

4 points

Feb 10, 2022 7:05 PM in response to Grant Bennet-Alder

Removed all drives, cards (including GPU), and the single riser and still the same results. Same diagnostic LEDS, no system fans and no power LED.

Some older machines would come to life holding the power button while it's unplugged, then plugging in while holding, so I tried this too. When I do this both OT A and OT B light up red even though the system is

powered off, and all other LEDS are off (Replicated what I mentioned above). When I press the power button all system fans run full blast but it still doesn't chime or boot. While powered the same green diagnostic LEDs light up when I press the diagnostic button.

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Mac Pro 3,1 won't boot after suspected RAM riser failure

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