How do PCs send 'power-off' signal to monitor?

By robo_dev ·
I just bought a flashy Belkin KVM switch to run two computers off one keyboard/video/mouse.

Everything works just peachy, except: Monitor will not go into standby mode. So the poor monitor just sits there with the Dell 'loss of input signal' message, with the power on, forever.

Anybody know how it works?

Is the method configurable in software, or this just a hardware thing?

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i think

by jck In reply to How do PCs send 'power-of ...

not for sure, but:

1) the OS does power management, and will power monitors off based on that

2) when the monitor loses power, it goes into green mode (energy star or whatever) and after a time it will hibernate too.

i think it's just about how the monitor reacts to the OS turning off and on power to the signal for the picture.

i've never had a monitor you could configure tho. so, i can't say u can set the monitor...just the Windows OS.

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After doing more may be a cable issue....

by robo_dev In reply to i think

As it turns out, there are three VGA standards, and they all use a DB-15 cable (VGA, VESA DDC1 and DDC2). Standby-mode is invoked thru what's called DPMS (display power mgt signaling)

The difference is that some older VGA cables, to save money, do not use all the pins, and/or tie some pins together.

The way it works is that the standby mode is invoked by dropping out pin5 horizontal synch. When both horiz/vertical are dropped the monitor goes 'no signal'. Further, the newer standards is what makes plug and play work (pin 12 is the data line for plug and play, and removing this pin makes plug and play stop working).

I know I grabbed whatever VGA monitor cable I found in the wire-bin....I bet I grabbed an old one with the old-school pinout, and therefore the DPMS won't work.

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May not be just a Cable Issue here

by OH Smeg In reply to After doing more research ...

Depending on the KMV Switch it may be that not all of the used Pins are wired inside the switch.

Besides dropping the H & V Sync Signals there are 2 extra Pairs Green Power used in the DB15 Cables. You have the standard RGB Pares and the Vertical & Horizontal Sync Pairs which amounts to 10 Wires and then a Common Earth being the Eleventh Wire which is the Shield around all of the Pairs and connects to the metal case of the socket and then the 2 Power Saving Pairs which brings the wire count used inside the Cable to 15.

Some KMV Switches to save costs only use the RGB and Sync Pairs and connect these internally. This saves a lot on money in the actual Switch not needing as many Pass Through Contacts and the only cure here is to replace the switch with one from a different Model or maker that supports the 15 Wire VGA Connections.

Remember this internal Switch switches the 15 Wires in the Video Signal the 7 Wires inside the PS2 Mouse Lead and the 7 wires from the Keyboard so the switch has to switch 29 Wires on each use. To make cheaper KMV's the makers reduce this to 25 or fewer by making all the Earth Connections Common and Unswitched as it saves them lots of money for the actual switch.


[e]Edited because I can not add up properly.

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vga pin out help - no standby

by mbean In reply to May not be just a Cable I ...

Hello, I read your post about the monitor standby issue - I have a media player that only has pins for RGBHV and then 2 wires tied to shield... If I want my monitor to go into standby/power save mode what pins would I need to connect? pin 5? and would I tie it to ground or +5?



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See links

by robo_dev In reply to vga pin out help - no sta ...

I'm not sure I understand what you're trying to do?

Do you want to force standby with a switch or something like that?

I think if you just drop vsync it goes into pwer save. if you drop V and H, it goes 'no signal'.

VESA DPMS power saving

This power saving mode is controlled by changing the sync signals according the table below:

H-sync On Off On Off
V-sync On On Off Off
Pwr lvl 100% 80% 0W <8W

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RE: I think if you just drop vsync it goes into power save

by OH Smeg In reply to See links

Only if the monitor itself supports Power Saving Option if it doesn't support this Option those Wires are not used and you need to turn the Monitor off when you do not want to use it.

So I don't really see much difference between forcing a Monitor into Power Saving by flicking a Switch and turning it off other than the very obvious by turning it off you save even more power and allow the monitor to last longer.


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