What could cause a failure to display anything on the HDMI output?

Question

Occasionally when I power up my friendly RPi the screen stays blank as if there is no output from the HDMI. I can still ssh to the device, so it is working.

Can anyone suggest reasons why it may be happening and how to fix it?

Answer 1

This was due to incorrect settings in /boot/config.txt.

Actually deleting the config file solved my issue, but its purpose and possible parameters are documented here.

The contents of my file were:

hdmi_mode=19
#arm_freq=800
disable_overscan=1

This is what comes by default in Arch. The hdmi_mode=19 setting sets the HDMI output to 1024x768 85Hz, which is apparently an unsupported resolution for my monitor.

I believe that deleting the file sets the output to hdmi_mode=1, which is VGA. Clearly this is suboptimal, so I recommend experimenting to find the best value.

Answer 2

Another possibility I came across is that I didn't get any display unless the HDMI cable was plugged in before the Pi was switched on.

Should be a relatively quick one to fault-find, but worth documenting here nonetheless.