Mac Mini 2012 not detecting dual monitors

[thisguyneil]

First time poster, if this belongs somewhere else/isnt allowed please be patient with me
Hi,

I have used my 2012 Mac Mini (MD387LL/A) with my 27 inch LG monitor (27MP33HQ) for years without any problem, but recently I've picked up a Samsung 24 inch curved monitor (CF390 24'') and wanted to run dual monitors. I have had my 27inch monitor plugged into my mini using the standard HDMI port on the back of the machine, and I have had a spare mini display to HDMI adaptor (Sabrent Mini DisplayPort (Thunderbolt) to HDMI Adapter [4K Support] (DA-MDHA)) lying around and thought I would just plug that into the back of my mini and plug an HDMI cable from that to my second monitor. So whatever monitor is plugged into the main HDMI port on the back works fine and is detected, but whatever is plugged into the mini display port using that adaptor does not. Its not detected, no signal, etc. I then plugged the adaptor into my macbook air and to a monitor and it works fine, no problems at all. I did a little research into passive and active mini display port adaptors and thought maybe my adaptor was passive and wasnt allowing a connection. So i ordered (Active Mini DP to HDMI, CableCreation 6 Feet Mini DisplayPort (DP1.2) to HDMI Cable, DP to HDMI, 4K X 2K & 3D Audio/Video, Eyefinity Multi-Screen Support, 1.8 Meters/Black) a new adaptor and when it came in im still having the same issues, nothing connecting to the mini display port is detected. With the first adaptor (sabrent) whatever was plugged into that adaptor, when you turned it on both monitors reset and would sometimes turn the main monitor (whatever was plugged into the HDMI port on the mac mini) into a blank black screen after flashing for a second. Then when you turn off the monitor thats connected through the adaptor the main monitor turns back on. I have swapped out HDMI cables, I have tried both monitors in several different combinations, and now i have tried two different kinds of adaptors. I have completely shut down my mini and turned it back on, its on the latest OS as of 9/19/2018, i just do not know what to do.

 

[Partron22]

USB to VGA adaptor -shudder-
You seem to have tried all the other combos.
Maybe they make a USB to HDMI nowadays?
Had same trouble on a 2014 Mini. I just swapped displays around until I got a pair that worked together.
I think it has something to do with the Mac not waiting long enough for some monitors to go through boot, before the Mac decides the connection is empty.

 

[thisguyneil]

USB to VGA adaptor -shudder-
You seem to have tried all the other combos.
Maybe they make a USB to HDMI nowadays?
Had same trouble on a 2014 Mini. I just swapped displays around until I got a pair that worked together.
I think it has something to do with the Mac not waiting long enough for some monitors to go through boot, before the Mac decides the connection is empty.

At this point I’m willing to try anything to get it to work. Any combination of adaptors.

 

[marclondon]

I'm running a 2012 Mini with two monitors - they both run fine off cheap DVI adapters (obviously one to HDMI, the other to displayport).

Screens are an Eizo and a LaCie.

Poss your problem is no DVI port on the monitor? I seem to recall an issue with HDMI.

 

[thisguyneil]

I'm running a 2012 Mini with two monitors - they both run fine off cheap DVI adapters (obviously one to HDMI, the other to displayport).

Screens are an Eizo and a LaCie.

Poss your problem is no DVI port on the monitor? I seem to recall an issue with HDMI.

I’m willing to try DVI if that would work, obviously I have no preference. Also yes I definitely have scanned all inputs on both monitors

 

[marclondon]

I’m willing to try DVI if that would work, obviously I have no preference. Also yes I definitely have scanned all inputs on both monitors

Well what are the input ports on your two monitors. You may have to get one with a DVI. Both of my monitors are 1920 x 1200 (one 24 inch and one 22 inch, unusually) and both have DVI but they quite old now - I suspect these are now hard to come by.

 

[MultiFinder17]

I've had such an issue with my own 2012 mini. It turns out that the Thunderbolt port is slightly loose, and wiggling it into the right position makes it work. Without it in just the right spot, I get no video.

 

[California]

First time poster, if this belongs somewhere else/isnt allowed please be patient with me
Hi,

I have used my 2012 Mac Mini (MD387LL/A) with my 27 inch LG monitor (27MP33HQ) for years without any problem, but recently I've picked up a Samsung 24 inch curved monitor (CF390 24'') and wanted to run dual monitors. I have had my 27inch monitor plugged into my mini using the standard HDMI port on the back of the machine, and I have had a spare mini display to HDMI adaptor (Sabrent Mini DisplayPort (Thunderbolt) to HDMI Adapter [4K Support] (DA-MDHA)) lying around and thought I would just plug that into the back of my mini and plug an HDMI cable from that to my second monitor. So whatever monitor is plugged into the main HDMI port on the back works fine and is detected, but whatever is plugged into the mini display port using that adaptor does not. Its not detected, no signal, etc. I then plugged the adaptor into my macbook air and to a monitor and it works fine, no problems at all. I did a little research into passive and active mini display port adaptors and thought maybe my adaptor was passive and wasnt allowing a connection. So i ordered (Active Mini DP to HDMI, CableCreation 6 Feet Mini DisplayPort (DP1.2) to HDMI Cable, DP to HDMI, 4K X 2K & 3D Audio/Video, Eyefinity Multi-Screen Support, 1.8 Meters/Black) a new adaptor and when it came in im still having the same issues, nothing connecting to the mini display port is detected. With the first adaptor (sabrent) whatever was plugged into that adaptor, when you turned it on both monitors reset and would sometimes turn the main monitor (whatever was plugged into the HDMI port on the mac mini) into a blank black screen after flashing for a second. Then when you turn off the monitor thats connected through the adaptor the main monitor turns back on. I have swapped out HDMI cables, I have tried both monitors in several different combinations, and now i have tried two different kinds of adaptors. I have completely shut down my mini and turned it back on, its on the latest OS as of 9/19/2018, i just do not know what to do.

Isn't this a High Sierra known problem? (Which is why I'm still on Mavericks)

 

[Neodym]

Same problem here: HDMI monitor working fine, TB monitor erratically not recognized (but lighting up every 30 seconds or so, indicating their has been some signal, but the picture would not come). So far I attributed it to DP1.1 in the 2012 mini’s HD4000 iGPU not suited well for multi monitor operation.

A loose TB port/connection possibly being the culprit is a new twist, but I’m willing to grasp for any straw, before I eventually give in and replace my 2012 mini with ... whatever else.

 

[ActionableMango]

At this point I’m willing to try anything to get it to work. Any combination of adaptors.

No signal conversion is necessary, so you shouldn't be using any adapter at all. Your Mac has Mini Display Port and your Samsung monitor has Display Port. Just get a cable with MDP on one end and DP on the other. This solution is cheaper, cleaner, and more reliable.

Using the On Screen Menu, set the Samsung Display Port version to DP1.1.

If this still doesn't work, you may have a faulty port like Neodym.

 

[Neodym]

If this still doesn't work, you may have a faulty port like Neodym.

I tend to believe that it's NOT a hardware fault. The port shows no signs of a bad connection, neither is it lose or the solder pads would look bad. Multiple cables show the same symptom, all sitting well when plugged in.

Instead, with a simple reboot, the screen is back in all glory. I don't even have to zap the PRAM. If I would stick to this setup (i.e. use the monitor for the mini exclusively), it would probably run until the mini (or the monitor) breaks. The problem arises when I start switching around the inputs on the DP monitor, so the mini goes from a dual display to a single display (and back when I switch back to the TB input on the monitor).

This looks very much like a driver/cache problem to me. Probably the software engineers at Apple don't have the scenario of someone using multiple computers in parallel not on their radar.

The problem seems to be persistent over multiple OSX ... errr macOS generations (had it first on ElCapitan and it's better, but still present in HighSierra - and probably in Mojave as well), but usually one does not completely rewrite a driver from scratch for a new OS release anyway.

 

[Neodym]

Just a small followup: As of Nov-2019, macOS 10.14 a.k.a. Mojave seems to finally have fixed the problem! Seems it was indeed a Software issue.

 

[davekro]

The issue with my mid 2012 Mac mini (Sierra 10.12.6) and identical dual Dell 24" monitors was that the (secondary) one that's connected to the small mini display port would go black (to sleep because it no longer sensed a signal from the Mac mini's display port): 1) seemingly for no reason during use, 2) upon restart on Mac, 'then' powering up both monitors. Someone mentioning it might be that the Mac was not allowing enough time for the Dell's boot up time, I shut down the Mac, powered both monitors up, when they both showed 'going to sleep', I then powered up the Mac. The right errant monitor worked too. I hope this is a consistent fix, not a random one. Thanks for the idea!

 

[tooloud10]

I've got the same problem with my second monitor running off the Mini Displayport. It's been doing this for years but it seems to be getting harder to get the second monitor to 'come to life'. The Mac Mini knows that the monitor is attached because I can see it under the Displays tab in System Preferences and I can 'click' on things on the blank screen...it just won't show an image without mucking around with the cables and power buttons, and sometimes rebooting the whole machine.

 

[Neodym]

What macOS version are you on?