Putting a monitor to sleep when no video signal

[soldar]

Other way round. Main board generates that signal to say it wants backlight on, and power supply turns on backlight.

That's what I said. We are in agreement. I think you misread or misunderstood.

OK, at this point I think I will begin by fitting a 5 volt relay to short that signal to ground. that way the activation is completely isolated. Once that is tested and working I will design a circuit that detects mouse activity and activates the relay after a certain time of no activity and keeps it activated until it detects furter activity.

It can be an extremely simple circuit except for the timer which will require some kind of counter because it needs to be anywhere between 10 to 30 minutes. I can do it with a 555 and a counter. It does not need any kind of precision.

Come to think about it, the monitor backlight should come on when the monitor is first turned on, without need for mouse activity. Or maybe not? i need to think about this.

[tom66]

Yes, I misread you.  Good luck with the hack. 

[soldar]

OK, I took out the PSU board and had a look. After some examination I found the components I was looking for. The resistor marked on the schematic as 2K2 was actually 6K8 .

The resistor is located near the connector while the capacitor is located close to the IC and there is a "long" track between them which, conveniently for me, half way along has a pad where I could solder a thin cable. I soldered a cable there and another to ground and drilled a small hole in the plastic back housing so I could take them outside.

After closing up the monitor and testing it the system does work; it blanks the screen when I short those wires.

When the monitor is on it uses 25W. When I blank the screen it goes down to about 12W, so half. (I am using one of those cheap watt meters that plugs in so I do not know how precise it might be with rectifier-capacitor loads.)

I am not sure how much effort I should invest into saving 12W although it is not only that but also that I just like the screen to go dark after a while. 

Maybe I can start out just with a countdown timer and reset it manually every once in a while

I need to think about this.

ETA: The more I think about this the more I think it just does not make sense that a modern monitor would not go to standby. I am thinking that maybe the "No signal from PC" message might last for a long time but not forever. I am going to test some more. Leave it overnight and see.