Grainy Screen

[hughvane]

Mac 2018 Mini, OS Mojave

I posted quite some while ago asking for monitor recommendations for the 2018 Mini. Financial constraints got in the way of further progress, but I'm back seeking knowledge and advice this time.

See image. That is what greets me from the Samsung [24" via HDMI, approx 3 years old] monitor once the Mini is reactivated after auto-sleep (ie. no activity for perhaps 15 minutes to 3 hours). The only fix is to switch the monitor to Standby and then back on again. Very occasionally that needs to be done 2-3 times.

What I would like to know is if the experts recognise a monitor issue, or a wake-from-sleep issue with the Mini's graphics function. Sometimes things wake up and function normally, eg. after being put to all-night sleep from the black apple menu.

OnyX finds nothing wrong with the System.

 

[chscag]

Should be easy enough to find out if it's the monitor or cable. Do you have another monitor or even a TV that you can attach to the Mini? Another HDMI cable should also be substituted if possible.

I doubt if it's the GPU since that's integrated within the CPU on that model Mini. You can always try resetting the SMC but it likely won't help.

 

[MacInWin]

Could it be that the monitor is shifting inputs when the Mini sleeps and stops sending video signals? That image looks like the "snow" that appears with no input. (Just in passing, I read many years ago that that kind of static is caused by the background radiation created at the Big Bang.)

 

[hughvane]

Update: I neglected to mention that the connection from Mini to Samsung is - now was - via an HDMI splitter, which made it much simpler to switch between the two Minis when operating to the single monitor. MacInWin may therefore have a valid point, although there is only the one HDMI port on the monitor, other inputs are VGA and USB, neither of which have ever been used.

Connection is now cable directly between the Mini & monitor. I shall give it a week of trials before throwing a hissy fit and rushing into purchasing a new monitor.

Thanks for the inputs.

 

[pigoo3]

Connection is now cable directly between the Mini & monitor.

I would think a direct connection like this would eliminate many possible connection issues...assuming the video cable is fine. Then any issue would either be the computer (hopefully not)...or the monitor itself.

Has this setup eliminated the grainy screen issue?

Nick

 

[hughvane]

[QUOTEHas this setup eliminated the grainy screen issue?
Nick[/QUOTE]

Unfortunately, no, but Phase II is changing the cable within the next couple of days. My gut instinct is a monitor fault, but more testing required.

 

[MacInWin]

Take a look at the monitor user guide to see if there is a way to set the default input to what you want and to lock it in. I still think it is shifting inputs when it loses the signal as the Mac goes to sleep.

 

[hughvane]

Take a look at the monitor user guide to see if there is a way to set the default input to what you want and to lock it in.

Thank you, that process is underway, but is very fiddly. I'll report back.

I still think it is shifting inputs when it loses the signal as the Mac goes to sleep.

My question about that is "if the monitor goes into grainy screen mode* when it cannot find an active source, why then doesn't it transfer back automatically when the source is reactivated, namely the Mini woken from sleep?"
*I'd have thought it more likely simply to go blank.

I realise this is more a Samsung issue than Mac, but from (fickle) memory, I did not encounter this issue until 2019, perhaps a year or so after I'd bought the Mini. The problem has been more pronounced in the past year.

 

[MacInWin]

My question about that is "if the monitor goes into grainy screen mode* when it cannot find an active source, why then doesn't it transfer back automatically when the source is reactivated, namely the Mini woken from sleep?"

"Grainy screen mode" is actually just "no incoming signal" which leaves the snow you see. The snow is caused by random electrons moving in the circuits in the absence of a signal. Most modern design has thresholds below which the screen just goes dark, but I guess that monitor doesn't have that engineered in. In the "old days" of early CRT monitors (and televisions), you would see that snow any time you tuned in a channel with no signal. And there is an accompanying sound of "white noise" that goes along with it. Again, modern equipment is usually designed with thresholds below which the screen is black and the sound is off.

As for your situation, I can imagine a design that says the default input is "x" but a user can set up the input to "y." If the "y" goes away, after a while the monitor reverts to "x" input. Now if I designed it, I would poll the ports and if "y" reappeared, I'd go back. But maybe they didn't do that because they wanted to avoid a situation where the user had two inputs connected, set to be looking at "y" but it went to sleep for a few minutes so the monitor reverted to "x" but the user came back and woke up the "y" input the monitor would not know what to do. Stay with "x" or go to "y?" So, it could be the design is that if it goes back to the default, it stays there unless manually changed. I'm guessing here, so all of this could easily be dead wrong. However, the way the monitor seems to handle empty inputs (the snow) would imply that they didn't design much sophistication into this particular monitor.

 

[hughvane]

"Grainy screen mode" is actually just "no incoming signal" which leaves the snow you see. .....
As for your situation .... it could be the design is that if it goes back to the default, it stays there unless manually changed .... the way the monitor seems to handle empty inputs (the snow) would imply that they didn't design much sophistication into this particular monitor.

I really appreciate the amount of thought and time you're putting into this issue.

Update: using instructions from the User's manual, I have set the Samsung Input selection to Manual, and selected the only source shown (a bunch of numerals and letters). So far, when left alone for anything ranging from 5 mins to an hour, the monitor has resumed normal display. That in turn suggests the cable and ports are okay, but I will change the cable again next week, meantime keeping a watch on the screen behaviour after waking.

Slightly off-topic, but parallel, what brand of monitor does Apple use in its iMacs?

 

[pigoo3]

Slightly off-topic, but parallel, what brand of monitor does Apple use in its iMacs?

From what I understand...LG seems to be the supplier of the display panels for Apple iMac's.

Nick

 

[pigoo3]

...I have set the Samsung Input selection to Manual, and selected the only source shown (a bunch of numerals and letters). So far, when left alone for anything ranging from 5 mins to an hour, the monitor has resumed normal display. That in turn suggests the cable and ports are okay, but I will change the cable again next week, meantime keeping a watch on the screen behaviour after waking.

I've messed around with a lot of external monitors...and as you probably know...many external monitors have their own built-in multi-level menus for various settings...and many times they can be VERY difficult to navigate with the 3-4 buttons located somewhere on the perimeter of the display (usually the bottom area).

Not quite as simple as:

* attach the video cable between computer & monitor
* plug in the power cable to the monitor
* turn on the computer
* set the monitor resolution in Apple Menu preferences (if it's not auto detected)

I had to setup a new computer & external monitor for my wife recently...and it was an absolute nightmare to navigate the built in menus of the monitor before we finally got the settings correct & everything working as expected.

- Nick

 

[hughvane]

Not quite as simple as:

Thank you Nick, will try what you've outlined on Monday morning when I change the HDMI cable. Meanwhile, the grainy screen issue has recurred a couple of times since my most recent post, very annoying.
[Aside - I recall printer problems being 'cured' by following removing their power source altogether, and then reconnecting in a predetermined sequence.]

The monitor setting in SysPrefs is the default for the S'sung monitor.

 

[hughvane]

Update: changed to brand new HDMI cable on Mon morning. Connected directly between S'sung monitor and Mini (no splitter involved). I have managed to replicate the snowy screen behaviour twice, both times after manually putting the Mini to sleep and switching off (to standby) the monitor while absent from the computer for an hour or more. The workaround is to switch the monitor off and on again. I have also added pulling the plug from the Mini end while the monitor is off, then plugging back in again, but I don't know if that makes any difference.