2 Monitors on MacMini M1

I just purchased the MacMini fully loaded and 2 LG 24” 24MD4KL-B. I am having problems getting the 2nd monitor to work, it should work if plugged into the HDMI port with an USB-C HDMI adapter which I purchased but it is not, nor will it work plugging it into second Thunderbolt 3 port. Late yesterday I finally got to a AppleCare senior adviser, he could not figure it out. The issue has been referred to Apple Engineering, the Advisor promises a response by tomorrow - we’ll see.

Stay tuned I’ll post an update.

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This is a well-known problem.

I guess I’m lucky. I connected both of my 24” HDMI monitors to my Macmini today, did several reboots, and everything is working fine so far. No flickering, no blank screens.

@Donsanborn, you’ve probably been through all this already but just in case…

  • Is the adapter a bi-directional / HDMI to USB-C adapter OR only a USB-C to HDMI adapter?
    • Some of the adapters I’ve had in the past only work one way.
  • Does the monitor / cable / USB-C - HDMI connection work when it’s the only monitor plugged in?
    • Is this a dual monitor issue or a problem with the setup for one of the monitors.
  • Does each monitor work when connected via USB-C one at a time
    • does each monitor actually work?
  • Does the HDMI port of the Mini work ok if connected to a TV: HDMI to HDMI?
    • i.e. prove out that the HDMI port got soldered on correctly! :wink:
  • Does the USB-C / HDMI adapter work ok when setup the other way?
    • Use the adapter to connect to USB-C on the mini to a HDMI TV - rule out the adapter being completely duff.

My approach would be to first confirm that each component works ok in isolation.
My personal unsubstantiated, wild speculation here is that HDMI to USB-C conversion is the problem.
Everything I’ve seen for HDMI to USB-C always seems to assume you’re going from a video source of USB-C to a HDMI display, not the other way.
Most of the M1 multi-monitor setups I’ve seen involve some sort of Dock or Hub so it might be you can have the Mini & these 2 monitors working but have to be a little more creative with the bits joining them together.

Fingers crossed you get this sorted :slight_smile:

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Stu, thanks so much for your reply. All of your suggestions are logical and helpful. I lack a lot of the proper equipment to perform the tests suggested. I have elevated the problem to the Apple Engineering Dept thru a Senior Advisor, I exchanged emails with that team earlier today without any progress yet, but am optimistic they will come up with a solution.

tonycap,
Could you please share the specifics on how you configured the 2 monitor to feed from on HDMI port? Are the monitors in mirroring mode or independent?

Thanks so much

Don

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I’d be happy to, it may be easier if you ask for the specific settings though.

I don’t think I needed to do any configuration changes.

I plugged in 1 HDMI cable to the HDMI port, did the OS update and installed 1Password and a few other TV essential programs.

I had to reboot a few times because the App Store app updates wouldn’t install.

After spending an hour or so installing SW using 1monitor, I then connected the second HDMI monitor to a USBC-HDMI adapter.

If I remember correctly the displays do not come up in mirrored mode, that is both monitors are independent of each other.

If I’m wrong about the mirrored mode NOT being the default, that would be the only configuration change I made is to not mirror the monitors.

(Why would anyone want both monitors to show the same display anyway?)

If you need more information just ask.

I’m happy to take a picture if you like, I’m not using any dock or other special equipment.

Believe me- I did this blindly and all by feel, fully expecting fir the second port not to work at all.

If it helps, I bought the Apple USB-C to HDMI adapter when I ordered the Macmini. I normally don’t like overpaying for connectivity such as this, but wanted to make sure I had everything I needed to get the Macmini up and running from the beginning.

TonyCap, thanks for your speedy reply. Please share the following:

  • monitor manufacture and model of the 2 connected to the MM. Mine are LG 24" 24MD4KL sold by Apple, but I got mine at B&H.

  • do the monitors have HDMI ports? Mine only have USBC and Thunderbolt ports

  • I don’t find an Apple HDMI (male) to USBC (male) adapter, I bought the J5create adapter at BestBuy and it is not compatible with BigSur.

  • I just got the Upgrow USB C to HDMI Cable 6FT 4K@60Hz USB Type C from Amazon and will try it this morning.

The saga continues.

@Donsanborn I had 2 LG 4k monitors I was using with my Intel MBP, and was also experiencing the issue of not being able to run both of them. TL;DR - get this: Siig HDMI to USB-C Port 4K 60Hz Converter Adapter

The problem for me has been two USB-C displays. It’s easy to find a USB-C source to HDMI display cable, but they are almost all unidirectional and won’t work the other way around. I looked long and hard for something that could go from an HDMI source to a USB-C display.

I just got this in and can confirm it works at 4k resolution, 60hz. You hook the HDMI into the Mac Mini, USB-A power to the mini USB plug on the dongle, and the USB-C out to the other monitor. Since you need to plug both HDMI and USB-A in for the dongle to work, you might need another USB/Thunderbolt hub (I had an OWC Thunderbolt 3 Dock that works just fine to give me additional ports).

The downside of this is that the monitor’s USB ports do not work. This doesn’t really bother me (I don’t trust the USB ports on the LG monitor anyway), but just so you know.

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ASUS VE248 Monitors, with native HDMI ports ( I can’t tell you which HW spec revision though, without looking up the specs).

I’m using a Belkin USBC-HDMI adapter bought from Apple’s website when I ordered the Macmini. However, I’m sure they have many sources for these adapters. If you ordered one from Apple now you may get an adapter from a different Mfgr

How can an HDMI adapter not be compatible with an OS?

I seems strange to me as well, but there is a clear and specific warning on their website stating the J5 is not comparable with Big Sur.

This problem has been turned over to the Apple Engineers by my Senior Advisor, I am hoping to hear their answer in the couple of days. This capability is clearly stated on the Apple website as a feature of the MM M1.

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Mike
I just received the SIIG HDMI to USBC that you suggested. I started the MM cold with both monitors and USB -A power cord plugged in, all that happened was the monitor with USBC flashed the HDMI monitor did not show any signs of life. I’ll try a few reboots, do you have any suggestions?

Thanks for your help

I had my Mac Mini powered on and one monitor (TB—>USB-C) connected, then:

  1. Connected the SIIG to the Mac Mini via HDMI
  2. Connected the USB power to an empty USB-A
  3. Connected USB-C to my other monitor

It showed up after about 2 seconds. Have had no problems since.

EDIT: Not sure it makes a difference, but I’m on 11.1.

As of lately, one of my HDMI ports goes out of sync when the Macmini goes to sleep. I have to reseat the USBC-HDMI adapter to fix it.
It’s always the same port though.

I’m using the Macmini to Remote Desktop to my Windows laptop. Sometimes the ledt&rigth RD displays get swapped. Not sure how much of that is the Macmini or the RDP app

FWIW I have had zero issues with monitors waking from sleep with the M1 Mac Mini. Used to have one not wake from sleep often with the old MBP, however.

Will finally yesterday I got the solution to 2 monitors on the new M1. It is really quite simple and wish that Apple’s Spec Sheet make it clearer. I think I told you that I got 2 new 24” LG monitors to go with the new CPU. The LG monitors only have USB-C ports (2 of which are Thunderbolt), the MacMini only has 2 USB-C Thunderbolt ports and one HDMI 2.0 and will only drive one monitor thru the USB-C ports. The second monitor must use the HDMI output from MacMini and go into a monitor with an HDMI input Not thru an adapter!!. So my 2nd new LG is being returned and I am now shopping for another with the correct port configuration. This solution was worked out with an Apple Genius who just happened to be taking calls on the AppleCare line.

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