MP 1,1-5,1 5,1 Mac Pro not booting (no chime no display), even after Logic Board replacement

[HeliosArm]

Hi,

Mac Pro suddenly stopped booting after turning itself off while idle. Two Xeon CPU's with 5,1 flashed, RX 580, faster ram etc.

Things I've tried:

• SMC Reset

• SYS RESET pressed on the board (no power going to keyboard for PRAM reset)

• Replacing battery

• Replacing GPU (also tried original GT120)

• Reseating and swapping round DIMMs

• Reseating and cleaning/re-pasting both CPUs

• Only using CPU A

• Inserting an old 4,1 configured CPU tray with RAM to match

• Removing peripheral PCI devices

• Replacing Logic Board that was pre-flashed to 5,1 (did this today and no dice).

I'm at my wits end here, I simply can't figure out what's causing this issue. Diag LED's look normal etc and have done throughout the entire debugging process (apart from the GPU OK LED flashing straight after replacing the Logic Board, re seated some stuff and it's now normal).

Any advice?! Cheers.

 

[tsialex]

Are you sure that the replacement backplane is really cross-flashed to MP5,1 firmware? Did you tested it before?

The PSU was tested with another known working Mac Pro?

 

[HeliosArm]

Thanks for your reply tsialex.

I have only the seller's word to go by, but since I also tried it with a 4,1 CPU configuration (which didn't work either) I assume that's not the issue?

I haven't had the chance to test/swap the PSU yet (feeling a little burned out on replacement parts 😅) but will do ASAP. The reason I left it so late was that the deeper I dug about the issue the more people said it was less likely to be the PSU.

The fans spin, even on the GPU with the 6-pin power connected - could it still possibly be the PSU?

 

[tsialex]

The fans spin, even on the GPU with the 6-pin power connected - could it still possibly be the PSU?

Sure, for one example, too low voltages can cause exactly what you describe.

The main point is to be absolutely sure that you have a working PSU and then eliminate it from the diagnostics. Mac Pros are too complex to diagnostic, you have to be absolutely methodical and you can't jump any steps.

Start testing your PSU with a known working Mac Pro, then the CPU tray - one at a time.

 

[HeliosArm]

Sure, for one example, too low voltages can cause exactly what you describe.

The main point is to be absolutely sure that you have a working PSU and then eliminate it from the diagnostics. Mac Pros are too complex to diagnostic, you have to be absolutely methodical and you can't jump any steps.

Start testing your PSU with a known working Mac Pro, then the CPU tray - one at a time.

Thanks for the advice - will do that ASAP and post an update.

 

[HeliosArm]

Update: managed to borrow a tested & working PSU from a friend and it's still not working!

Not sure where to go from here. Tried putting in the old 4,1 CPU tray again for good measure (and swapping out RAM) and no boot. Something's obviously gone!

 

[tsialex]

Disconnect the front IO board, any SATA devices, check again if you can get at least a chime. Sometimes is a short with a SATA drive, the DVDs or the front IO board.

Also, test both CPU trays with your friend's working Mac Pro.