HP U28 4k HDR is not recognized when connected to a Macbook

[ophilippsen]

Hello all,

this week I stumbled upon a rather strange behavior of the HP U28 monitors.

A brief description of my setup:

- 1x Macbook Pro, i9, 16GB RAM, 512GB SSD, Macos 10.15.7.
- HP Thunderbolt Dock G2, 120W
- 2x HP U28

Macbook -- thunderbolt --> HP Dock G2 -- displayport --> 1. HP U28
                                                                             -- usb-c --> 2nd HP U28

The 2nd HP U28 is connected via usb-c cable because the Macos does not support MST, and therefore the 2nd displayport in the HP Dock cannot be used.

Both monitors have been working great for the last few weeks after solving the MST problem.

This morning I encountered a strange phenomenon:

- I come into the office and connect my Macbook to the HP Thunderbolt G2 and nothing happens.
- ok, I think to myself, the dock has hung up, I connect one of the monitors to my Mac, but nothing happens
- ok, then I try it with another adapter, nothing happens
- I turn the monitor on and off, nothing happens
- ok - I swap the Macbook for another one, connect the monitor, nothing happens

**bleep**, that can't be - then a thought comes to my mind - does the monitors firmware have a problem maybe ? How about disconnecting the monitor from the power supply - and lo and behold, after I disconnected both monitors once, they work normally again.

But what is the cause ?

Do the monitors need a firmware update ?

How can I report the problem to HP so that someone can take a look at it ?

Has anyone of you ever had a similar problem ?

I would be glad about feedback !

Oliver

[joevt]

you said "-- usb-c --> 2nd HP U28". I think you meant Thunderbolt port since the USB-C DisplayPort Alt Mode port is part of the MST Hub.

You were able to solve the problem by restarting the display (disconnecting and reconnecting power). Has this problem occurred more than once? I've had to do this with some other displays.

The support site doesn't have any firmware updates for your display.

[ophilippsen]

Yes you are right - I connected thrue the thunderbolt on the hp thunderbolt dock g2 to the second U28.

BUT - this problem does occur on both monitors, even when connected by the display port.

I had this problem several times.

Just today I played with the monitor settings in Mac OS.

After switching from 4k to scaled 2k, and back to 4k the switched monitor does not show any picture and is black.

The display shows the "cable is not connected" message.

Switching on/off by using the button did not help.

After disconnecting and reconnecting power it works again.

I will try to figure out a "replayable" test case to provocate the issue.

I would like to report this issues to hp, but do now know where ?
Do you know, where to place bug reports ?

[joevt]

Does the problem occur when connected directly to the MacBook Pro, or to a different Thunderbolt device?

How old is your HP Thunderbolt Dock G2? There is a firmware updater but you need to use Boot Camp/Windows to install it. You may need to install Thunderbolt driver if the one included with Boot Camp doesn't allow the firmware update. In that case, I believe you need to make sure you don't get the DCH Thunderbolt driver.

In your test of switching from 4K to scaled 2K, did the display show an image while at 4K? And at scaled 2K? And then not work when switched back to 4K?

The AGDCDiagnose command can show how the display is connected to the GPU and what resolution and pixel format it's using. Maybe you can use it before and after each step to see what's changing each time.

/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_test1_4K.txt 2>&1

SwitchResX can be used to see the timing info of the resolutions that you try (double click the resolution in the Current Resolutions tab for the display in SwitchResX).

As for contacting hp tech support, I guess first you should go to support.hp.com, login, add your HP devices (dock and displays) to My Dashboard (take a picture of the serial numbers and enter them). There's a bunch of options on the My Dashboard page. You can go to Contact Support, click on one of the products, then do a Chat. There's also a Business Support option but I don't know anything about that.