Since a while I'm running Debian server (no GUI) and in the beginning the monitor was being detected, but since the installation I solely connect via ssh to my server and everything seemed to work just fine.
Now I came across the situation that I had to connect the monitor again as I could not ssh in anymore and connected the same screen again, but unfortunately there was not display at all. So I had no other option to power cycle the MacMini Server.
I started trying to trace down the problem, but as a beginner I didn't get very far :-(
Please find below a few details I could gather so far.
$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
$ sudo dmesg | grep HDMI
[sudo] password for admin:
[ 70.873123] input: HDA Intel PCH HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:1b.0/sound/card0/input11
[ 70.873194] input: HDA Intel PCH HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:1b.0/sound/card0/input12
[ 70.873276] input: HDA Intel PCH HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:1b.0/sound/card0/input13
$ cat /sys/class/drm/*/status
disconnected
disconnected
disconnected
disconnected
disconnected
connected
disconnected
$ hwinfo | sed -n '/LCD Monitor/,/^$/p'
41: None 00.0: 10002 LCD Monitor
[Created at monitor.125]
Unique ID: rdCR.zEftk1FcUKA
Parent ID: _Znp.Ag8gOVmx9nF
Hardware Class: monitor
Model: "MX27UC"
Vendor: AUS
Device: eisa 0x27a2 "MX27UC"
Serial ID: "GCLMRS022323"
Resolution: 720x400@70Hz
Resolution: 640x480@60Hz
Resolution: 640x480@67Hz
Resolution: 640x480@72Hz
Resolution: 640x480@75Hz
Resolution: 800x600@56Hz
Resolution: 800x600@60Hz
Resolution: 800x600@72Hz
Resolution: 800x600@75Hz
Resolution: 832x624@75Hz
Resolution: 1024x768@60Hz
Resolution: 1024x768@70Hz
Resolution: 1024x768@75Hz
Resolution: 1280x1024@75Hz
Resolution: 1152x864@75Hz
Resolution: 1280x720@60Hz
Resolution: 1280x960@60Hz
Resolution: 3840x2160@60Hz
Size: 597x336 mm
Year of Manufacture: 2016
Week of Manufacture: 52
Detailed Timings #0:
Resolution: 3840x2160
Horizontal: 3840 4016 4104 4400 (+176 +264 +560) +hsync
Vertical: 2160 2168 2178 2250 (+8 +18 +90) +vsync
Frequencies: 594.00 MHz, 135.00 kHz, 60.00 Hz
Driver Info #0:
Max. Resolution: 3840x2160
Vert. Sync Range: 30-75 Hz
Hor. Sync Range: 31-135 kHz
Bandwidth: 594 MHz
Config Status: cfg=new, avail=yes, need=no, active=unknown
Attached to: #37 (VGA compatible controller)
The strange thing in the above output is that it doesn't change if I connect a monitor from another brand, well I did not reboot, but nevertheless shouldn't a change of the monitor not be detected automatically?
During boot the following is displayed
sudo journalctl -b | grep "i915"
Jul 30 19:02:21 MacMini kernel: i915 0000:00:02.0: [drm] VT-d active for gfx access
Jul 30 19:02:21 MacMini kernel: i915 0000:00:02.0: vgaarb: deactivate vga console
Jul 30 19:02:21 MacMini kernel: i915 0000:00:02.0: [drm] Using Transparent Hugepages
Jul 30 19:02:21 MacMini kernel: i915 0000:00:02.0: [drm] DMAR active, disabling use of stolen memory
Jul 30 19:02:21 MacMini kernel: [drm] Initialized i915 1.6.0 20201103 for 0000:00:02.0 on minor 0
Jul 30 19:02:21 MacMini kernel: snd_hda_intel 0000:00:1b.0: bound 0000:00:02.0 (ops i915_audio_component_bind_ops [i915])
Jul 30 19:02:21 MacMini kernel: fbcon: i915drmfb (fb0) is primary device
Jul 30 19:02:21 MacMini kernel: i915 0000:00:02.0: [drm] fb0: i915drmfb frame buffer device
So, I decided to connect an 10 year old monitor and reboot, the monitor is recognised, but there is still no output!
$ hwinfo | sed -n '/LCD Monitor/,/^$/p'
41: None 00.0: 10002 LCD Monitor
[Created at monitor.125]
Unique ID: rdCR.I4isrNo_UP2
Parent ID: _Znp.Ag8gOVmx9nF
Hardware Class: monitor
Model: "Viseo223DX"
Vendor: PKB
Device: eisa 0x037a "Viseo223DX"
Serial ID: "D2WEE0084206"
Resolution: 720x400@70Hz
Resolution: 640x480@60Hz
Resolution: 640x480@67Hz
Resolution: 800x600@56Hz
Resolution: 800x600@60Hz
Resolution: 1024x768@60Hz
Resolution: 1024x768@70Hz
Resolution: 1920x1080@60Hz
Resolution: 1280x1024@60Hz
Size: 477x268 mm
Year of Manufacture: 2013
Week of Manufacture: 37
Detailed Timings #0:
Resolution: 1920x1080
Horizontal: 1920 2008 2052 2200 (+88 +132 +280) +hsync
Vertical: 1080 1084 1089 1125 (+4 +9 +45) +vsync
Frequencies: 148.50 MHz, 67.50 kHz, 60.00 Hz
Driver Info #0:
Max. Resolution: 1920x1080
Vert. Sync Range: 50-76 Hz
Hor. Sync Range: 30-83 kHz
Bandwidth: 148 MHz
Config Status: cfg=new, avail=yes, need=no, active=unknown
Attached to: #37 (VGA compatible controller)
Hopefully there are some knowledgeable folks out there who could give me a hint or two...
Many thanks in advance for any help!