xset dpms force off not working 4.3inch DSI LCD

Any difference if you use an explicit display number? e.g

xset -display :0.0 dpms force off xset -display :1 dpms force off

using the first one I get - server does not have extension for dpms option xset: unknown option force

And using the second I get - xset: unable to open display ":1"

wild guess:

sudo xset dpms force off

I tried sudo in fron of all the above commands with the same results

sudo xset dpms force off gives xset: unable to open display ""

My skill in these things is limited as you have probaly guessed!!!

xset(1) is a utility supplied with and for X11, and requires a) running X server, b) a known display on that X server, and c) permissions to access and modify that display.

If you try to use xset(1) to blank a screen, you have to specify the display that the screen is attached to, and give permission (either implicitly, by "owning" that display, or explicitly through xauth(1) or another recognized authorization method) for the xset(1) client application to access that display.

All to say that xset(1) is /not/ the best tool to use to blank a screen remotely.

What you likely need is to use vbetool(1) or some other video hardware state altering tool (perhaps setterm(1) would do) to set the low-level video blanking values.

HTH