General monitor question: screen resolution relay?

[Jim Adney]

In all the VGA & SVGA monitors I've used there seems to be a relay
that clicks when the screen rate changes. I'm guessing that this is
just a relay that switches in/out some C to change a timing circuit
for the H or V sweep.

Is this for the H, or the V, or both? Is there more than 1 relay?

I've actually looked for this relay, but I don't see it. Can someone
give me some general clue as to where I should be looking. Does this
part not actually LOOK like a relay?

Or do I have entirely the wrong idea about this click I hear when
changing resolutions?

thanks,

-

 

[William R. Walsh]

Hi!

In all the VGA & SVGA monitors I've used there seems to be a relay
that clicks when the screen rate changes. I'm guessing that this is
just a relay that switches in/out some C to change a timing circuit
for the H or V sweep.

There is often this as well as one that is used to turn on and off the
degauss coil in some "better" designs.

I don't know exactly what the relays do, but I've been told that they are
used to select different voltages off of the main power supply for each mode
that the monitor supports.

I would guess that monitors doing this mode switching "silently" are of
higher quality, but I like my monitors to "click" and "clack" when the input
signal changes. Such audible feedback is hard to ignore and has been helpful
a few times to troubleshoot video card problems.

Is this for the H, or the V, or both? Is there more than 1 relay?

Yes, there may be more than one relay, especially in a monitor that supports
a wide range of scan rates and resolutions.

I've actually looked for this relay, but I don't see it. Can someone
give me some general clue as to where I should be looking. Does this
part not actually LOOK like a relay?

It should look like a relay, but it's probably a good deal smaller than it
sounds. Monitor cabinets seem to make good amplifiers for the natural (and
sometimes not so natural) sounds of the electronics inside.

Or do I have entirely the wrong idea about this click I hear when
changing resolutions?

The click is either A) a degauss coil being engaged or B) the monitor's
circuitry using relays to select the appropriate voltages from the power
supply. On some it may be a combination of both.

William

 

[James Sweet]

In all the VGA & SVGA monitors I've used there seems to be a relay
that clicks when the screen rate changes. I'm guessing that this is
just a relay that switches in/out some C to change a timing circuit
for the H or V sweep.

That's precisely what it does.

Is this for the H, or the V, or both? Is there more than 1 relay?

It's in the horizontal circuit, that's the only one that's resonant.

I've actually looked for this relay, but I don't see it. Can someone
give me some general clue as to where I should be looking. Does this
part not actually LOOK like a relay?

Usually they're just a black or blue box on the board, so yeah they look
like ordinary relays. It'll be somewhere around the horizontal circuit so in
the same general area as the flyback and the yoke plug.

 

[Asimov]

"Jim Adney" bravely wrote to "All" (26 Aug 04 21:10:10)
--- on the heady topic of "General monitor question: screen resolution relay?"

JA> From: Jim Adney <[email protected]>

JA> In all the VGA & SVGA monitors I've used there seems to be a relay
JA> that clicks when the screen rate changes. I'm guessing that this is
JA> just a relay that switches in/out some C to change a timing circuit
JA> for the H or V sweep.

JA> Is this for the H, or the V, or both? Is there more than 1 relay?

JA> I've actually looked for this relay, but I don't see it. Can someone
JA> give me some general clue as to where I should be looking. Does this
JA> part not actually LOOK like a relay?

JA> Or do I have entirely the wrong idea about this click I hear when
JA> changing resolutions?

JA> thanks,

I think the click results from the change in scan frequency
rearranging the surface static charge around the deflection coil. Kind
of like the snap of a whip. The change in frequency alters the raster
size, so a correction must be made by adding/removing different
impedances to the deflection system, usually at the output. A relay
could be used but it is cheaper and much more reliable to use
transistors or powerfets. Which explains why you can't even find a
relay!

A+s+i+m+o+v

.... I worked hard to attach the electrodes to it.

 

[Alex Bird]

"Jim Adney" bravely wrote to "All" (26 Aug 04 21:10:10)
--- on the heady topic of "General monitor question: screen resolution relay?"

JA> From: Jim Adney <[email protected]>

JA> In all the VGA & SVGA monitors I've used there seems to be a relay
JA> that clicks when the screen rate changes. I'm guessing that this is
JA> just a relay that switches in/out some C to change a timing circuit
JA> for the H or V sweep.


I think the click results from the change in scan frequency
rearranging the surface static charge around the deflection coil. Kind
of like the snap of a whip. The change in frequency alters the raster
size, so a correction must be made by adding/removing different
impedances to the deflection system, usually at the output. A relay
could be used but it is cheaper and much more reliable to use
transistors or powerfets. Which explains why you can't even find a
relay!

I think there's two separate sounds here. I can recall monitors
making either or both of these sounds. The second is more subtle
usually.

Alex

 

[Sam Goldwasser]

I think there's two separate sounds here. I can recall monitors
making either or both of these sounds. The second is more subtle
usually.

Agreed. On some monitors, there are definitely relays, which will click
whether the deflection/HV is working or not.

But there is always a more subtle sound associated resolution changes
due to a variety of effects.

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