Mac mini USB C / Thunderbolt connection to monitor

[mph999]

Hey Guys,

Anyone got any ideas on this, it has me a little stumped ....

Short Version

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New Mac Mac mini works fine with LG monitor connected via thunderbolt / USB C using same cable as old Mac mini
Old Mac mini which was connected the same way, and had worked for several years has suddenly stopped working with the monitor via thunderbolt/ usb c
No changes made, other than disconnecting and reconnecting
USB C cable is good
USB /Thunderbolt ports on old Mac mini are working (mouse/ trackpad connected fine)
Old Mac mini works fine via HDMI

Long Version

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I took the jump and upgraded my Mac mini to the new M4 model.

Previously, my 'old' (intel based) Mini was connected to my LG monitor via one of the thunderbolt ports - all working absolutely fine.

I connected the new Mini the same way, no issues - booted, recovered all my files via migration assistant - all good.

This evening I went to wipe the old Mac, with the intent to sell - popped the USB cable out of the new machine, back into the old - booted, and nothing at all on the display - I've not touched anything, other than the cable. (Machines were powered off when I removed/ plugged in the cable).

Tried a reboot, different ports - nothing.

Connected the monitor back to the new Mac, booted - and absolutely fine - in fact I am using it to type this.

Connected the old Mac to a different monitor via HDMI (that monitor has no USB c port) - that worked OK, was able to wipe the machine.

Tried again, reconnected to my main LG monitor, nothing ....

I know the USB ports are working as I connected a keyboard and trackpad ... just not with the monitor.

Any ideas gratefully received ....

mph999

[LunarOne]

I've recently got a new Mac Studio M4 Max connected with USB-C to two HP LP2475W monitors using their displayport connectors. I don't know whether they are using "Thunderbolt' or USB3.0. My monitors are still connected to the old computer via DVI and to another computer via HDMI. One thing I noticed is that my monitors did not auto-switch to the displayport inputs because I had configured the monitors that way. I needed to press the scan button to get the monitor to detect the signals, and then the Quick Select button to switch inputs.

I wonder whether there's something similar going on. Could it be that your old Mac mini isn't sending the right signal for the monitor to automatically detect the right input and switch to it? Have you tried checking the monitor menus so see whether it can see anything connected on the USB/Thunderbolt input?

[mph999]

LunarOne said:

I've recently got a new Mac Studio M4 Max connected with USB-C to two HP LP2475W monitors using their displayport connectors. I don't know whether they are using "Thunderbolt' or USB3.0. My monitors are still connected to the old computer via DVI and to another computer via HDMI. One thing I noticed is that my monitors did not auto-switch to the displayport inputs because I had configured the monitors that way. I needed to press the scan button to get the monitor to detect the signals, and then the Quick Select button to switch inputs.

I wonder whether there's something similar going on. Could it be that your old Mac mini isn't sending the right signal for the monitor to automatically detect the right input and switch to it? Have you tried checking the monitor menus so see whether it can see anything connected on the USB/Thunderbolt input?

Good theory, but nope ...

I only moved the cable from the back of the new Mac to the old - so it's using the same import on the monitor.
However, I did try flicking round the inputs - nothing (Only have three, HDMI, Displayport and USB).

I actually have my work laptop also connected to the LG monitor - the old Mac mini used to switch to the right input automatically.

I'm inclined to agree it's something along these lines though - there is no way on earth x4 USB C ports have suddenly stopped working, just at the point I unplugged and then (well a day later) plugged it back in - plus I know the ports work as I had a keyboard/ trackpad plugged in.

Edited by mph999 on Thursday 10th April 00:45

[megaphone]

Have you tried powering down the monitor, unplugging the power, and restarting?

Is there a setting on the monitor for 'auto sensing' the resolution? Maybe the M4 is outputting a higher res and the monitor has switched and stayed there?

[Magnum 475]

Another thought - check that you have a 'proper' Thunderbolt 4 cable, rather than a cheap USB-C cable. I've been bitten by this - USB-C cables are not all the same. I have a Dell docking station that gets used with a number of laptops. As it has a short cable, I bought a USB-C extension. Some laptops will only work if i don't use the extension, whereas lower resolution displays work fine with the extension - I must get round to buying a proper Thunderbolt 4 extension to solve this problem.

So, USB-C display is very sensitive to cables. It's possible that the new Mac is pushing higher res / refresh rate, and the cable won't cope.

[mph999]

Magnum 475 said:

Another thought - check that you have a 'proper' Thunderbolt 4 cable, rather than a cheap USB-C cable. I've been bitten by this - USB-C cables are not all the same. I have a Dell docking station that gets used with a number of laptops. As it has a short cable, I bought a USB-C extension. Some laptops will only work if i don't use the extension, whereas lower resolution displays work fine with the extension - I must get round to buying a proper Thunderbolt 4 extension to solve this problem.

So, USB-C display is very sensitive to cables. It's possible that the new Mac is pushing higher res / refresh rate, and the cable won't cope.

Cable is good - it was working before I unplugged it, and had been working for 5 odd years.
The new Mini is running on the same cable, no. issue at all.

I had made a mistake, the cable is actually USB-C (thunderbolt) -> HDMI, I thought it was plugged into a thunderbolt port on the monitor, but nope, it HDMI - not that that makes a difference to the issue.

I can get another cable just to prove that is defo not related, never a bad idea to have a spare as I only have the one.

I reset the nvram last night, still no go ....

[mph999]

Just to close this off - bought a new Ankar thunderbolt cable - connected the old mini to by second monitor and it’s working fine.

Makes no sense …

If I can be bothered I’ll connect it back to my main monitor on the old cable and see if ‘what ever it was’ has cleared, off if it’s really the new cable.