I already have two windows lap tops on my desk. One is mine, one is the one I use for work. Because I have limited desk space and don't want to be moving peripherals from one machine to the other I got an old fashioned (VGA) KVM switch. 

This works fine for the two windows machines. I can toggle between them using the keyboard.

What doesn't work is my Pi 4. If I connect the monitor, mouse and keyboard directly into the PI then everything works, but I can't use it via the switch.

The connection for the video is a bit messy, because the monitor on my desk is an old VGA unit. So the connections from PI to monitor are

1. Micro HDMI to standard HDMI adaptaor
2. HDMI to VGA converter
3. Output from the converter goes into the monitor.

And all that works

When I connect to the KVM switch then the chain lengthens a little

3) Out from the converter goes to the switch
4) Switch connects to the monitor

Then I get no video.

The signal path for my work windows machine is

1) HDMI output into HDMI to VGA converter (different brand than I use with the PI)
2) Output from the converter to the KVM switch
3) Output from the switch into the monitor

So one less link in the chain because I don't need the micro to standard HDMI adaptor. 

Any ideas as to why the PI doesn't seem to work through the switch? Or seems to not work? With no video I can't tell.

Edited June 23, 20215 yr by Bobster
Better title

@Bobster, should have quoted you...

Don't have a KVM switch, but with a HDMI switch (3 sources, one display) the PI4 also didn't work correctly, get rid of switch, all good... but this is also a HDMI/mDP/DP display, I'm guessing with the VGA, there isn't enough feedback to the PI4 to enable it to select the right video mode, from the switch, there is a possible hard setting you can force in the /boot/config.txt

Edited July 28, 20215 yr by Kalahari Meerkat

Thanks. It does seem that the Pi4 doesn't do well with switches, but I'll try looking in config.txt. 

If I can find an HDMI switch I'd have to replace my monitor as well. And I'd need a VGA -> HDMI converter for one machine 

14 hours ago, Bobster said:

replace my monitor

My HDMI switch is just video, but apparently there are KVM switches that do HDMI & USB, then you'd only need one HDMI to VGA converter on the output of the KVM to your monitor, I'd imagine...

Ja, I have limited desk space so need to share the input devices as well as the monitor.

Initially I was running my servers and certain other kit via hardware switches, they proved to be a royal PITA eventually....

Run the Pi headless (No monitor) and on it enable/install VNC Server (VNC Overheads are minimal) - From your windoze pc, access the Pi via "VNC Viewer" ... Problem solved... Been doing it for years and it works really well... (Controls Windows/Linux/etc perfectly..)