nMP + 10.13.5 + HDMI = no stable sync?

[damezumari]

I have used my nMP (D500, 32GB) for few years with various issues every now and then; notably resume from standby crashes GPU so I don't. Currently I use two displays, Acer HK321 and Dell UP3214Q (both 4k).

With 10.13.5 there seems to be a new interesting issue; if I connect one of my displays via HDMI (and I should, as there is no 4k output over thunderbolt in login screen?), the screen goes black every few seconds, and sometimes re-syncs again and sometimes now. This makes that display unusable via HDMI.

Same display is still fine over thunderbolt (aka mini displayport), and the behavior started with 10.13.5, so I suspect that is the culprit. I guess I will have to try the HDMI cable with different computer to be sure, but I am very surprised if it broke down just as I upgraded to 10.13.5.

I wonder if I should just downgrade the AMD drivers or revert to a TM backup, this is somewhat .. annoying.

 

[axantas]

They did indeed remove the 4K output during startup - so no bootlogo, no possibility to visibly select the startvolume. BUT, this came back with a system update a couple of month ago. There were one or two Firmware Updates. Maybe you should try to "iron over" a combo-update for your nMP.
>> just let it run. As you are "blindfolded", you will just sit in front of a black screen and see your Mac reboot several times. It will take quite some time. Do not interrupt it! (or connect the not really working HDMI monitor for this procedure.)

 

[mikeboss]

I'm running an EIZO (1900x1200) off the HDMI port on my MacPro6,1 and I don't see the symptoms you're describing with macOS 10.13.5.

 

[axantas]

The flickering symptoms once existed indeed - I guess it was brand specific DELL particularly, in MacOS AND Bootcamp. One could avoid it by forcing the monitor to use 50Hz - which is quite a hassle.
I don't know how and when, but It was eliminated after quite some time.

 

[damezumari]

It turns out it was probably false alarm (loose cable?), it seems that once I rebooted (thanks to it deciding not to fire up displays at all today after a day of not being used) and reconnected cables HDMI is once more fine. Still no picture on displayport-based 4k/60hz monitor setup at boot so second monitor at end of 30hz HDMI is helpful. I wonder if combo update would fix it..

 

[damezumari]

I was being optimistic; I restarted machine yesterday, this morning HDMI connected display is again going on and off every few seconds. Sigh.. I guess I will be using time machine to try previous version next when I have to motivation (for now, just using one display).