LCD MOnitor Pops n Hisses When Unplugged

[ShadowTek]

I bought a KDS K22mdwb LCD monitor yesterday.
http://www.kdsusa.com/K22mdwb.asp

Today, as I was leaving my house, I performed my ritual of switching off
the breakers to every non-esential electrical device. After turning of
the power to the monitor, it started making poping, whining, and
gurgleing noises. The sounds were coming from the monitor's speakers
(which aren't even connected to my computer).

I listened to the sounds for about a minute, and it showed no signs of
winding down or stopping anytime soon, so I tried disconnecting the DVI
cable, which immediately stopped the sounds.

Is there any way to eliminate this feedback, short of installing a damn
switch on the DVI cable?

Could this be a symptom of a hardware failure, or is this simply to be
expected when removing the monitor's grounding path?

This is the first monitor I've owned that has built in speakers, so I've
never had an opportunity to experience this problem before.

The new monitor is still working fine, and I used my old LCD monitor for
eventless years while routinely turning off its power breaker every time I left
the house.

 

[ShadowTek]

I would advise also shutting down and powering off the PC,
or at least, hibernating and killing the PC's power.

This computer serves several functions that require it to be on 24/7.

 

[Paul]

I bought a KDS K22mdwb LCD monitor yesterday.
http://www.kdsusa.com/K22mdwb.asp

Today, as I was leaving my house, I performed my ritual of switching off
the breakers to every non-esential electrical device. After turning of
the power to the monitor, it started making poping, whining, and
gurgleing noises. The sounds were coming from the monitor's speakers
(which aren't even connected to my computer).

I listened to the sounds for about a minute, and it showed no signs of
winding down or stopping anytime soon, so I tried disconnecting the DVI
cable, which immediately stopped the sounds.

Is there any way to eliminate this feedback, short of installing a damn
switch on the DVI cable?

Could this be a symptom of a hardware failure, or is this simply to be
expected when removing the monitor's grounding path?

This is the first monitor I've owned that has built in speakers, so I've
never had an opportunity to experience this problem before.

The new monitor is still working fine, and I used my old LCD monitor for
eventless years while routinely turning off its power breaker every time I left
the house.

Does the monitor have a button on its interface, to shut off the backlight
and remain in standby ? That allows the adapter to remain running, feeding
the monitor, without the monitor's operating life being shortened. That
leaves the ground connection intact. While it might still waste 1 watt
of electricity, it might be a bit quieter.

The only power path on the DVI cable, would be the +5V pin used to power
DDC/CI serial interface. Pin 14 here, sends power from the computer to
the monitor's serial EEPROM chip, so that the computer can read out
resolution information, even if the monitor is turned off.

http://en.wikipedia.org/wiki/Digital_Visual_Interface

If the monitor was completely unpowered, that +5V pin is the only
way I can think of, for significant power to come down the cable.
And then the question you'd have to ask, is why is a sneak path available
inside the monitor, from that pin ? The +5V on the cable, should
really only be wired to the serial EEPROM that contains resolution
information, inside the monitor. And diodes should be used, so that
monitor power, and +5V cable power, share nothing in common. (The usage
of the diode, would be to prevent reverse power flow.)

As an experiment, try connecting the computer to the monitor using a
VGA cable, and use a VGA cable where pin 9 is missing. See if it runs
quiet after that, using your breaker trick.

http://en.wikipedia.org/wiki/VGA_connector

Paul

 

[GlowingBlueMist]

I bought a KDS K22mdwb LCD monitor yesterday.
http://www.kdsusa.com/K22mdwb.asp

Today, as I was leaving my house, I performed my ritual of switching off
the breakers to every non-esential electrical device. After turning of
the power to the monitor, it started making poping, whining, and
gurgleing noises. The sounds were coming from the monitor's speakers
(which aren't even connected to my computer).

I listened to the sounds for about a minute, and it showed no signs of
winding down or stopping anytime soon, so I tried disconnecting the DVI
cable, which immediately stopped the sounds.

Is there any way to eliminate this feedback, short of installing a damn
switch on the DVI cable?

Could this be a symptom of a hardware failure, or is this simply to be
expected when removing the monitor's grounding path?

This is the first monitor I've owned that has built in speakers, so I've
never had an opportunity to experience this problem before.

The new monitor is still working fine, and I used my old LCD monitor for
eventless years while routinely turning off its power breaker every time I left
the house.

Having a monitor and computer on different outlets and especially
different breakers can cause problems if a ground loop develops. Due to
corrosion either at the outlet or at the breaker panel the ground and or
neutral leads may not be exactly at the same ground potential. This
results in what is commonly known as a ground loop.

Problems like yours is one reason why when I worked in IT we always
tried to have the monitor and computer on the same outlet or outlet
strip. Same with anything else directly attached to the computer such
as speakers and printers.

This is the kind of thing that drives audio technicians nuts in large
installations and may result in that pesky 50/60 cycle hum that creeps
into a system and tries to stay.

Possible ground problems can be detected by measuring between the ground
leads of both outlets and also by doing the same between the two neutral
connectors. There should be zero volts between the two grounds and
between the two neutral connections.

Caution... Doing the test incorrectly could result in an electrical
shock large enough to kill a person. In the USA, if the two breakers
are on opposite phases of the power companies transformer you could see
220 volts between the two hot wires which will ruin a perfectly good day...

What I would do is next time you turn off the breaker of the monitor, if
the sound shows up, unplug the monitor from the wall outlet and see if
the sound quits. If it does then most likely you have a grounding issue
between the two outlets.

Fixing a ground problem is better left to a professional as it may
entail removing the wires from the breaker box, cleaning them of any
corrosion however minor, and reattaching them. The same may need to be
done at the wall outlets.

Next time you power off the breaker to the monitor and the sounds turn
up try unplugging the monitor from the wall outlet and see if the sound
goes away. If it does you most likely do have a grounding issue that
needs to be fixed, if not then it's a component going bad either in the
monitor/speaker or the video card/computer.

 

[ShadowTek]

Having a monitor and computer on different outlets and especially
different breakers can cause problems if a ground loop develops.

They are plugging into different surge protector strips, but those are
both plugged into the same wall outlet.

Next time you power off the breaker to the monitor and the sounds turn
up try unplugging the monitor from the wall outlet and see if the sound
goes away. If it does you most likely do have a grounding issue that
needs to be fixed, if not then it's a component going bad either in the
monitor/speaker or the video card/computer.

I unplugged it from the strip the first time it happened,
and the sounds continued uninterrupted.

 

[GlowingBlueMist]

They are plugging into different surge protector strips, but those are
both plugged into the same wall outlet.


I unplugged it from the strip the first time it happened,
and the sounds continued uninterrupted.

Sounds like you have ruled out a grounding issue.

Beginning to sound more like a component issue as the others have
mentioned. At this time it sounds more like it was at the PC end of the
equation.

Like Paul and Ian D suggested, it sounds like something from the PC is
supplying a voltage to the monitor/speakers that it should not. If you
are using a PC video card try switching over a motherboard video
connector (if your motherboard has one) and see if that helps, or add a
video card if you are already using a built in motherboard video port.

Problems like this can be a real pain to troubleshoot as it could be
just about anything related to the video port or power supply. Trying
another video cable would not be out of the realm of possibilities as
well... Good Luck

 

[ShadowTek]

Sounds like you have ruled out a grounding issue.

Beginning to sound more like a component issue as the others have
mentioned. At this time it sounds more like it was at the PC end of the
equation.

Like Paul and Ian D suggested, it sounds like something from the PC is
supplying a voltage to the monitor/speakers that it should not. If you
are using a PC video card try switching over a motherboard video
connector (if your motherboard has one) and see if that helps, or add a
video card if you are already using a built in motherboard video port.

Problems like this can be a real pain to troubleshoot as it could be
just about anything related to the video port or power supply. Trying
another video cable would not be out of the realm of possibilities as
well... Good Luck

I connected the monitor to another computer, one with an AGP graphics
card, used the same DVI cable, and this time there weren't any persistant
noises, just that one last burp from the speakers.

I guess this means that the problem has been here all along, and I just
didn't notice it until I got a monitor with speakers.

I'm awaiting the delivery of a new Nvidia Geforce GTS 250, so
I'll see how that one does.

It didn't do any apparent damage to my old LCD monitor.

 

[J G Miller]

I connected the monitor to another computer, one with an AGP graphics
card

In the original computer, was the DVI output from on-the-motherboard
graphics or from a PCI-e graphics card?

 

[ShadowTek]

In the original computer, was the DVI output from on-the-motherboard
graphics or from a PCI-e graphics card?

It's an nvidia gefore 9600GT PCI-E.

The motherboard it's connected to doesn't have onboard graphics.

 

[GMAN]

This computer serves several functions that require it to be on 24/7.

You are worried to the point of paranoia about vampire devices in your home
yet leave the one device that draws the most electricity on?

 

[GMAN]

This computer serves several functions that require it to be on 24/7.

Also , the monitor, left to go into sleep mode will only draw 1-2 watts of
power. thats less than 1/4 of what a hall nightlight draws.