Mac Pro 5,1 multiple GPU’s having same flickering issues

[Swervin81]

Hey. I bought a MP 5,1 (an actual legit 2010) and it came in a couple weeks ago. Unfortunately, it’s been a bumpy ride. When I turned it on, the boot screen appeared on screen just fine but once the OS loaded up, it crapped out and started flickering like crazy, alternating between a black screen (no signal) for a second or two and the actual display for a brief flash, with a few instances of static snow in there. It made even the OS install process a nightmare. After I got back to the seller, they told me it may be a GPU or CPU issue, so they sent me an HD 4870 as replacement for the stock 5770 and a replacement CPU tray with the same processor. I receive them both today, pop the 4870 in, and... same flickering issue, but even worse. It starts off alternating between display and static snow, then drops signal every now and then.

And I did indeed test my monitor with other devices (Lenovo laptop through VGA and Win10 PC through same DVI-D input as I tried on Mac). It worked perfectly there. I tested it with another monitor, same issue on the Mac front. Swapped CPU trays, same issues. Tried resetting SMC, PRAM, NVRAM, cMOS. Everything.

I’m totally stumped at this point. If it’s not the monitor or CPU... there’s no way I could have such rotten luck that I’ve gotten 2 bum GPU’s in a row, right?

 

[h9826790]

Sounds like they gave you two bad GPU in a roll.

Can you take a photo of the GPU and post it here?

 

[Naimfan]

Return it.

While it's possible you got two bad GPUs, it seems more likely that there's a problem elsewhere.

 

[JedNZ]

I had similar screen artefacts when I installed my Sapphire Nitro R9 380X (via DP cable). I overlooked the cable for weeks thinking it was my GPU and/or logic board/PCIe slots etc, but eventually replaced the DP cable and the problem went away immediately. I know it sounds like a simple fix, but using a different video cable might be all that's going on here.