Mac Pro 5,1 with AMD/Gigabyte r9 280X

danallen

macrumors member
Original poster
Oct 8, 2018
48
20
Houston
The display on a Mac Pro 5,1 is blacking out for a second or two at times that seem random. I am hoping you will be able to help me fix this problem.

BACKROUND
I read that replacing the stock Radeon 5770 with AMD r9 280X would suffice as a graphics card in a Mac Pro 5,1 upgrading to Mojave. With a Mac-Flashed edition of that card, the upgrade has come off without incident.

However, I have had problems with a Samsung U28d590 4K monitor connected to that card via displayport. Regardless of the screen resolution selected, the monitor goes black for a second or two.

This problem first appeared about a month before the stock Radeon 5770 was replaced, A brief visit with Google search combined with moving the displayport cable from one of the ports to the other solved the problem. Temporarily.

When the replacement card went into cheese grater, filling the slot made vacant by the departure of the Radeon 5770, the 1-2 second screen blackouts came back. At first, it seemed the obvious culprit is the "new" used video card, but that theory was undercut by a few considerations and then an experiment with a surprising result.

It's Not Necessarily the Graphics Card, Stupid.

Short screen blackouts happen on all kinds of computers for all kinds of reasons. A half hour visit to Google search on this topic will show you what I mean.

Unexpected Result of Experiment

Two mini displayport ports on the new video card means two monitors can be hooked up to the same card. I have two monitors, on my desk now. I expected when the Samsung monitor went dark, the other monitor would too, thus removing from the monitor from the list of suspected culprits. Here is what happened:

Unexected result 1: When the Samsung monitor went black for a second, the other monitor, (Asus 287 HD monitor) stayed lit. It never goes black.

Unexpected result 2: The frequency of black outs on the Samsung monitor fell from once every minute to a couple times all day.



 

danallen

macrumors member
Original poster
Oct 8, 2018
48
20
Houston
Has the Gigabyte R9 280X been efi flashed ?
yes.
I'm betting the Samsung monitor is the problem. I have a flashed R9 280X in my 5,1 and have no monitor problems.
That is my impression as well, based on the fact that when the Samsung and another monitor, happens to be from Asus, are both connected at the same time, each with its own displayport cable going into the minidisplayport ports on the card, side by side, I can see the Samsung blacking out while the Asus continues to run normally.

What monitor are you running?


Have you tried the Samsung monitor on another system, yet?
I have been running the Samsung for over a year on this computer, but with the stock Radeon 5770 card.



Can you think of any reason why this blackout problem goes away when booting with two monitors instead of one? One monitor is the Samsung 4k and the other is an Asus HD.
 
Last edited:

danallen

macrumors member
Original poster
Oct 8, 2018
48
20
Houston
Switched to hdmi cable, plugged into the hdmi1 port on the samsung U28d590. Had to hassle with the process for getting the monitor to switch from displayport to hdmi. The hassle is caused by the fact that once the monitor is connected to displayport, the button for bringing up the monitor's menu stops working. That problem is documented elsewhere. Carefully following the instructions, I found the magic key to getting the monitor to switch to hdmi. I have read in a few places this will eliminate the blacking out problem, at the price of reducing the frame rate from 60 fps to 30 fps. I didn't think I would notice the difference in frame rate, but that turns out to have been incorrect. Still, the slower frame rate beats the black outs.

It looks like the cost to fix this problem is a different 4k monitor. This one was way cheaper than any other I could find, and I would have to say the performance of this monitor is not great. It is 4k, which is nice, but it is noticeably less responsive, even for typing as I am now.

Also, the image is not as crisp with the hdmi connection as it was with the displayport.


**************************************

Another surprising result: System preferences for displays is set to 30 frames per second. Running Cinebench Open GL test, it scores 49 fps.
 
Last edited:
  • Like
Reactions: TheStork