Display connected to Raspberry Pi shows a blank screen

Nevermind, I got it working by switching to the first micro HDMI slot (closest to power input) and then following this guide

https://howtoraspberrypi.com/raspberry-pi-hdmi-not-working/#:~:text=This%20is%20probably%20the%20most,the%20file%20%2Fboot%2Fconfig.

I had exactly the same issue, thanks for this!

Our image per default just always uses the first display.
This was never a problem as all Raspberry Pi models had just one external hdmi port. The Pi 4 now has two and it seems that you have to use the one closer to the USB-C power input.

I've added this info to the setup guide in the FAQ.

Thanks for pointing this out!

Thanks for the reply.

As it happens I had the hdmi in the first port, next to the usb-c power connector. I just installed the v11 build earlier, on a new card and it did not work.

After following the above instructions and looking at the screen for a while, I realised that something was wrong, the circles weren't round in the dubbadhar theme.

A bit of digging revealed that the screen was being set to mode 4, which is 640 x 480.

My screen is an 800 x 480 hdmi touchscreen. I've no idea who the manufacturer is and I have a feeling that the edid information is not transmitted or received correctly (it used to be hooked up to a computer and it defaulted to something odd like 1280 x 800, I had to manually set i t to 800 x 480). I'm not really surprised that it's not being set up correctly.

Further searching led me to be able to force it to the correct resolution by changing , or adding, the following to config.txt :

hdmi_group=2
hdmi_mode=87
hdmi_cvt=800 480 60 6 0 0 0
hdmi_drive=1

I gathered this from lines #23 to #27 here : https://learn.adafruit.com/adafruit-5-800x480-tft-hdmi-monitor-touchscreen-backpack/raspberry-pi-config

I left this line in there as well, to make sure it used the correct port:

hdmi_force_hotplug=1

Screen looks much better now, with everything matching up to the browser view. I think I can say that my screen is now correctly configured.

I hope this will be of use to someone.

So I just had a look back at the default hdmi configuration of the image.

As you correctly noted the values were set to:

hdmi_group=2
hdmi_drive=1
hdmi_mode=4

I guess these stuck from testing and i failed to remove them afterwards before publishing the image.
I now reverted that back to being auto detected from EDID and uploaded a new v11_1 image.

Thanks a lot for pointing that out in detail!

Could you try and check if this version now works for you without having to manually edit the config.txt?

Thanks for the reply and for making the changes.

I've just tried it now. It does now detect the screen automatically so it's possible to get ‘up and running’ without any hassle.

However, for me, it doesn't set the resolution correctly, I think it sets it at 800 x 600, as the circular images are again oval. I think this is a problem with my screen, as I said it set up incorrectly in windows when connected to the pc.

I'm trying to get the current setup by using tvservice -s command but all I get is an error (failed to initialise VCHI (ret=-1) )

I also tried to read the edid info of my screen using tvservice -m, again the same error appeared.

Would I need to install vchi or activate it or something else?

Doesn't really matter, I don't mind adding these four lines to config.txt, and I've learnt a bit about things!

Here are what I have to add to get it working correctly:

hdmi_cvt=800 480 60 6 0 0 0
hdmi_group=2
hdmi_drive=1
hdmi_mode=87

From what I can gather:

hdmi_cvt=800 480 60 6 0 0 0 sets up a new DMT mode, mode 87. 

86 modes are normally defined for DMT, so this adds another to the list, defined as 800 x 480, 60Hz and aspect ratio 6, which is 15:9. The last three ‘0’ are defaults for margins, interlace and rb, no need to mess with them!

800 x 480 is a 5:3 aspect ratio (or 1.67:1) or, multiply by 3, 15:9, which is given as ratio 6 in a table at:

https://www.raspberrypi.org/documentation/configuration/config-txt/video.md

hdmi_group=2 force sets it to the DMT group

hdmi_drive=1 sets it to a DVI mode, (I believe the image part is the same as hdmi, just no audio - you can use a dvi output to drive a hdmi screen, just no sound, done it for years!)

hdmi_mode=87 this just selects the newly defined ‘mode 87’ set up above.

HTH.

Glad to hear you got it working correctly and found the configuration that fits for your screen :)

But people that aren't that familiar with Raspberry Pis or Linux most likely won't be able to figure out how to set these values so easily.
So the “possible to get ‘up and running’ without any hassle”  like you noted is exactly what we're aiming for.
I mean there's only so much that can be done and configured automatically. But it should at least be possible to connect a HDMI screen without having to first alter the configuration file before it works at all ^^

So thanks again for testing and bringing this issue up.

You are most welcome, I'm very glad to have been able to do anything to help. 

Excellent work guys, thank you very much!