Hi Dom and Gsh.
Thanks for your responses. Answers below:
1) Dom - obtained the library Pi400 and using their power supply and HDMI cable (both RPi certified) I get the diagnostic output you said I would get of HPD=1 and EDID=ok. I then just change the Pi400 for my Pi4B and no output on the monitor at all. I then repeated both tests with my power cable and HDMI cable, neither is certified, but I get the same results, ie. output as expected with the Pi400, nothing with the 4B.
2) Gsh - Running kmsprint on my Pi4B I get:
Connector 0 (33) HDMI-A-1 (connected)
Encoder 0 (32) TMDS
Crtc 3 (100) 1280x720@50.00 74.250 1280/440/40/220/+ 720/5/5/20/+ 50 (50.00) P|D
Plane 3 (89) fb-id: 721 (crtcs: 3) 0,0 1280x720 -> 0,0 1280x720 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 721 1280x720 XR24
Plane 57 (686) fb-id: 725 (crtcs: 3) 0,0 64x64 -> 464,203 64x64 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 725 64x64 AR24
Connector 1 (42) HDMI-A-2 (disconnected)
Encoder 1 (41) TMDS
which I like because it says the HDMI is connected and thus probably not a hardware fault. I then ran the same command on the Pi400 with everything the same including using the same SD card and got the following:
Connector 0 (33) HDMI-A-1 (connected)
Encoder 0 (32) TMDS
Crtc 3 (100) 1280x720@50.00 74.250 1280/440/40/220/+ 720/5/5/20/+ 50 (50.00) P|D
Plane 3 (89) fb-id: 722 (crtcs: 3) 0,0 1280x720 -> 0,0 1280x720 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 722 1280x720 XR24
Plane 57 (686) fb-id: 726 (crtcs: 3) 0,0 64x64 -> -2,-2 64x64 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 726 64x64 AR24
Connector 1 (42) HDMI-A-2 (disconnected)
Encoder 1 (41) TMDS
I note there are a few small differences in the outputs but I don't know if they are significant.
3) Dom -
Running raspinfo on my Pi4B gave this URL - https://pastebin.com/rieEqtnP
Running raspinfo on the Pi400 gave this URL - https://pastebin.com/Ri7zD0eE
All that was changed was the Pi4B for the Pi400, the same SD card and cables were used for both commands. I can see an EEPROM update is available for both Pi's but hopefully you can find something in the above to give me a pointer as to why the 4B won't provide an output.
Thanks for your responses. Answers below:
1) Dom - obtained the library Pi400 and using their power supply and HDMI cable (both RPi certified) I get the diagnostic output you said I would get of HPD=1 and EDID=ok. I then just change the Pi400 for my Pi4B and no output on the monitor at all. I then repeated both tests with my power cable and HDMI cable, neither is certified, but I get the same results, ie. output as expected with the Pi400, nothing with the 4B.
2) Gsh - Running kmsprint on my Pi4B I get:
Connector 0 (33) HDMI-A-1 (connected)
Encoder 0 (32) TMDS
Crtc 3 (100) 1280x720@50.00 74.250 1280/440/40/220/+ 720/5/5/20/+ 50 (50.00) P|D
Plane 3 (89) fb-id: 721 (crtcs: 3) 0,0 1280x720 -> 0,0 1280x720 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 721 1280x720 XR24
Plane 57 (686) fb-id: 725 (crtcs: 3) 0,0 64x64 -> 464,203 64x64 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 725 64x64 AR24
Connector 1 (42) HDMI-A-2 (disconnected)
Encoder 1 (41) TMDS
which I like because it says the HDMI is connected and thus probably not a hardware fault. I then ran the same command on the Pi400 with everything the same including using the same SD card and got the following:
Connector 0 (33) HDMI-A-1 (connected)
Encoder 0 (32) TMDS
Crtc 3 (100) 1280x720@50.00 74.250 1280/440/40/220/+ 720/5/5/20/+ 50 (50.00) P|D
Plane 3 (89) fb-id: 722 (crtcs: 3) 0,0 1280x720 -> 0,0 1280x720 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 722 1280x720 XR24
Plane 57 (686) fb-id: 726 (crtcs: 3) 0,0 64x64 -> -2,-2 64x64 (XR24 AR24 AB24 XB24 RG16 BG16 AR15 XR15 RG24 BG24 YU16 YV16 YU24 YV24 YU12 YV12 NV12 NV21 NV16 NV61 P030 XR30 AR30 AB30 XB30 RGB8 BGR8 XR12 AR12 XB12 AB12 BX12 BA12 RX12 RA12)
FB 726 64x64 AR24
Connector 1 (42) HDMI-A-2 (disconnected)
Encoder 1 (41) TMDS
I note there are a few small differences in the outputs but I don't know if they are significant.
3) Dom -
Running raspinfo on my Pi4B gave this URL - https://pastebin.com/rieEqtnP
Running raspinfo on the Pi400 gave this URL - https://pastebin.com/Ri7zD0eE
All that was changed was the Pi4B for the Pi400, the same SD card and cables were used for both commands. I can see an EEPROM update is available for both Pi's but hopefully you can find something in the above to give me a pointer as to why the 4B won't provide an output.
Statistics: Posted by BrianC3000 — Sat Jan 10, 2026 7:34 am