Hot switching a VGA signal

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I'm installing two security type DVR's that each have a VGA output. I would like to use one monitor with an AB switch, and switch between the two VGA DVR outputs. Can I damage anything with such an arrangement? Thanks, Lenny

 

[Cydrome Leader]

I'm installing two security type DVR's that each have a VGA output. I would like to use one monitor with an AB switch, and switch between the two VGA DVR outputs. Can I damage anything with such an arrangement? Thanks, Lenny

As long as the DVRs will always output a signal even if no monitor is
attached, there should be no problems. VGA stuff is birectional, although
not everything interrogates the monitor.

Even those rediculous beige steel boxes with the black knob would probably
be ok for the resolutions coming out of a security system.

 

[William Sommerwerck]

As far as I know, no monitor can be damaged by yanking the input signal. So
the "burp" while switching shouldn't be a problem.

The only way that I know of that a monitor can be damaged is if it's a
multi-sync model, and it's driven at a scan rate above its highest spec'd
rate. Other than that...

 

[Michael Black]

William Sommerwerck explained on 30/08/2013 :

I know this is OLD History but-
The early text only green IBM PC monitors needed a sync pulse from the CPU or
they would "self destruct"
The monitor was powered from the CPU power switch so that it cold not be left
on alone.
Of course that is really long ago history. ^^

That sounds more like legend. I had a couple of Ball Brother open frame
small monitors that I used back then, for my OSI Superboard and then my
Radio Shack Color Computer. They needed a horizontal sync signal to
generate the horizontal ramp (and the very high voltage), but if there was
no horizontal sync signal, nothing bad could happen.

Michael

 

[Michael Black]

Michael Black has brought this to us :

It is not legend.
I was very specific about which Monitor it was, text only green IBM PC
monitors ie the 5151.
I was in IBM Computer Support at the time. :-?

Okay, that's more defining. I wasn't sure if this was something you saw,
or something someone else said was true. A bit of information can be
worse than none at all.

Michael

 

[mike]

I'm installing two security type DVR's that each have a VGA output. I would like to use one monitor with an AB switch, and switch between the two VGA DVR outputs. Can I damage anything with such an arrangement? Thanks, Lenny

For convenience, it's hard to beat a KVM swtich.
I had a 4-monitor KVM. Switch button on the front
or hook up a keyboard and hot-key select.
Oughta be a zillion of 'em at surplus outlets.
The Two-port ones are a dime a dozen if you live in an
area with garage sales.

Also maintains signal continuity so you don't get
ghosting with long cables.

 

[Leif Neland]

Michael Black formulerede lørdag:

That sounds more like legend. I had a couple of Ball Brother open frame
small monitors that I used back then, for my OSI Superboard and then my Radio
Shack Color Computer. They needed a horizontal sync signal to generate the
horizontal ramp (and the very high voltage), but if there was no horizontal
sync signal, nothing bad could happen.

Michael

I once had an *old* tube TV-monitor (from a TV station control room).

I had it connected to a Sinclair ZX-81, which use the CPU for also
generation the video signal.

The ZX-81 could be put in "Fast" mode, where it used all the CPU-time
for computing instead of video generation, so the video was not proper
synchronized.

This unsynchronized signal probably had a higher flyback frequency or
something, causing the high voltage to go bananas, so sparks flew,
which produced large bangs from inside the monitor.

When the monitor finally died, it got replaced with a B/W tv, where I
cut a trace from the tuner and applied the video signal to the pcb.

This ZX-81 later got fitted into a rack, with a wirewrapped 64Kb
expansion ram and 6 channel audio. Even later, the CPU lived on in a
CP/M-plus system with a whopping 3/4 MB ram. But that's another story.

Leif