Resolved Upgraded to Catalina 10.15.3 - no image via HDMI

djc6

macrumors 6502a
Original poster
Aug 11, 2007
591
135
Cleveland, OH
I upgraded from Mojave 10.14.6 to 10.15.3 today - everything seemed fine when the upgrade was done.

I then shutdown my mac mini and ever since, no picture on one of my LG 27UD58P-B 4K displays. I have one connected via HDMI, one connected via CableMatters USB-C to HDMI 2.0 cable:


I can use either display, but only via the USB-C cable - I can no longer get any picture on either monitor via HDMI. I don't have room for another USB-C cable due to other thunderbolt devices.

Any ideas whats going on? I saw a few threads in the fall about similar issue, but they don't have any recent posts.
 

ikaka

macrumors regular
Mar 5, 2009
135
22
SMC reset fixed it.

Shut down mac
Hold down power button for 10 seconds

Seems fine now!

Yup, I have to do that like 3-4times every time I reboot or cold boot, pisses me off. (and no I don't want an adapter, no room)
 

tstimper

macrumors newbie
Jan 29, 2020
29
0
today i found that removing power from the mac mini 2018 for some hours fixed HDMI.
But i expect that the issue will come back after the next update. You could test this. Make a backup, than internet recovery to Mojave -> HDMI ok -> than update to Catalina -> HDMI fail. Than the behavior would be confirmed at another Mac mini 2018. I have seen this with three different logigboards. This is #macmini2018hdmigate . Apple needs to fix this soon. Otherwise this device goes back to Apple ...
 

frou

macrumors 6502a
Mar 14, 2009
686
749
Unplugging power for several hours is basically doing the same as PRAM/NVRAM reset in background:

Isn't the whole point of the "NV" in NVRAM the exact opposite? i.e. that it doesn't require power to retain its contents.
 

tstimper

macrumors newbie
Jan 29, 2020
29
0
funny, a NVRAM (se https://de.wikipedia.org/wiki/NVRAM) wich is actually only a temporary NVRAM for some hours. But the point is that there could be a problem with NVRAM on Mac mini 2018 which corrupts stored settings and this breaks HDMI. #macmini2018hdmigate
 

ikaka

macrumors regular
Mar 5, 2009
135
22
confirmed, removing power for few hours restores hdmi on the 1 boot, vs pram/nvram reset takes 3-4 times.
 
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tstimper

macrumors newbie
Jan 29, 2020
29
0
ok, so NVRAM has corrupt data which breaks HDMI. Ckearing NVRAM fix this.
There are two questions:
1. which data get corrupt? Is there something we can do with a script to fix this?
2. is this normal behavior that NVWAM loose his data after some hours without power is is this a hardware error?
 

bsbeamer

macrumors 68040
Sep 19, 2012
3,476
1,768
Anyone with this issue have Windows/Boot Camp installed? Created major issues with corruption in MP5,1 and exacerbated with incorrect Windows install method. Most noticeable when trying to update firmware and unable. Required 3+ resets and even then occasionally would fail. Some needed manual cleanup by users. Beyond technical skill for many.