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UKenGB

macrumors regular
Original poster
Feb 21, 2010
147
38
Surrey, UK
I have a cMP 4,1 converted to 5,1 and happily running Mojave for several years. It has a Radeon RX 580 graphics card driving the above monitor from its DVI port and also 2 x 20" ACDs from the 2 mini DisplayPorts, via active adapters. This has been working fine for years.

Recently, when waking from sleep the 30" ACD will go black again within a minute and the windows get shuffled around. I found that powering off the 30" ACD had no effect, but unplugging from the DVI port and plugging back in again would bring the 30" back to life (and the menu bar would relocate to that display as it should be).

Initially this was only occasionally, but over the last few months it has become more common and now this occurs EVERY time after waking from sleep and requires more unplug/plug-in operations before it would come back to life, such that I use 'caffeinate' to prevent it sleeping when not in use as it works perfectly otherwise.

Anyone any idea if this is a monitor or graphics card problem?

I thought I could try swapping the monitors and ports around to try and determine if ACD or card problem, but the mDP->DVI adapters aren't dual-link.

I'll try PRAM and SMC reset, but can anyone suggest what might be causing this?
 

UKenGB

macrumors regular
Original poster
Feb 21, 2010
147
38
Surrey, UK
Resetting PRAM and SMC made no difference and swapping monitors on card ports shows that the problem is the ACD 30" monitor that is the problem, not the card.

It's a puzzle to me as to what can be the problem that allows it to wake perfectly from sleep, then go off after 10 secs or so. Whatever it is, it seems to be getting worse as this morning I was unable to get it working until a restart and much unplugging and plugging in of the monitor.

Suggestions as to the cause of this would be much appreciated.

Thinking further on this, could it be software related? Presumably MacOS stores the display config in some preference file(s) and can uniquely identify a monitor. So if that pref is corrupt in some way, the problem might follow the monitor on different ports, even though the hardware is actually ok?

Thoughts on this?
 

UKenGB

macrumors regular
Original poster
Feb 21, 2010
147
38
Surrey, UK
Sorted.

The problem was the Monitor/PSU sensing system. Preventing the 2 sensing terminals from making contact (some carefully applied insulating tape in the monitor's power lead plug) brought it back to life and no 'singing' sound that was previously emitted by the PSU when the monitor refused to work.

Several options for a more permanent fix, but this is now the second ACD that has failed due to this 'sensing' safety feature Apple built in. However when a safety feature itself is the first thing to fail, then it is clearly worthless, so any permanent solution will involve simply eliminating that sensing wire connection so it can cause no more grief.

Hope this might help others.
 
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UKenGB

macrumors regular
Original poster
Feb 21, 2010
147
38
Surrey, UK
I was wrong. It now appears to be nothing to do with the PSU sensing whatsoever.

What I later discovered is that once this 'blackout' has occurred (usually within 30 secs of waking up), it is disconnecting the monitor's video cable from the graphics card and its power cable from the PSU, then reconnect video cable and then power from its PSU that re-awakens the monitor. It has to be those connections or monitor will stay dark. Once working again, it will happily work perfectly for as long as the Mac Pro stays awake. I've not yet determined how long sleep has to be to cause the problem, but to be clear, the monitor is not just dark/black, it is no longer seen by the Mac and the Menubar and windows are shuffled around due to the now 'missing' display.

What is odd is that a 27" mDP/LED monitor works perfectly on this Mac Pro, with no blackout problem at any time.

Even more bizarre, this ACD 30" (and its PSU) works perfectly on a Mini I have available for testing, with no blacking out after wakeup.

So the problem is this ACD 30 on this Mac Pro (doesn't matter which port is used from the graphics card). Really need another Mac Pro and another ACD 30 in order to troubleshoot further, but I have neither.

There is of course the difference in the monitors I've tried as the ACD 30 is 1600 vertical lines and the 27 is 1440. Could that be the difference causing the problem? Seems unlikely as once I've shuffled the connections and got the ACD 30 running again, everything works perfectly (at full 1600 vertical resolution) until next sleep.

So basically, this has got me completely stumped. I have no idea why this ACD 30 blacks out within about 30 secs after wakeup when running from this Mac Pro, yet both the Monitor and the Mac Pro both work perfectly when used with other devices. Also, this ACD 30 has been running perfectly on this Mac Pro for the best part of 10 years, so whatever the problem is, it is not some fundamental mismatch between Mac and monitor.

Anyone got ANY idea what's going on here?
 
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