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VGA LCD flicker

T

TT

Jan 1, 1970
0
I am having a problem with a VGA LCD display device when powered from a
different AC power circuit to the video signal source (PC).

If both the LCD monitor and PC are plugged into the same power point,
everything works fine. The problem arises when I power the LCD from a
different power point on the other side of a warehouse. When powered from
different circuits, the LCD flickers or waves/pulses to what looks like a
50Hz type flicker.

I am using a VGA splitter to boost the video signal with a 30M VGA cable to
get across the warehouse floor. I am confident that this isn't what is
causing the problem because I have tried connecting the LCD directly to the
PC through a short 2M VGA cable and run an extension cord across to the
power point on the other side of the room to try and eliminate the cause. In
this case, the flicker is still apparent.

I have also tried a CRT monitor which exhibits the same problems. Also, if I
power PC and LCD together at either side using the same power point, there
is no problem, so I don't think it's a power problem at one particular
point.

Has anyone solved a similar problem before or have any ideas what might be
causing the problem? Thanks.
 
P

Phil Allison

Jan 1, 1970
0
TT said:
I am having a problem with a VGA LCD display device when powered from a
different AC power circuit to the video signal source (PC).

If both the LCD monitor and PC are plugged into the same power point,
everything works fine. The problem arises when I power the LCD from a
different power point on the other side of a warehouse. When powered from
different circuits, the LCD flickers or waves/pulses to what looks like a
50Hz type flicker.

I am using a VGA splitter to boost the video signal with a 30M VGA cable to
get across the warehouse floor. I am confident that this isn't what is
causing the problem because I have tried connecting the LCD directly to the
PC through a short 2M VGA cable and run an extension cord across to the
power point on the other side of the room to try and eliminate the cause. In
this case, the flicker is still apparent.

I have also tried a CRT monitor which exhibits the same problems. Also, if I
power PC and LCD together at either side using the same power point, there
is no problem, so I don't think it's a power problem at one particular
point.

Has anyone solved a similar problem before or have any ideas what might be
causing the problem? Thanks.


** The power points are possibly on different AC phases.

To check this use an extension lead and connect the probes of a DMM
between the two actives, if they are the same phase the reading will be
near zero volts - if different phases the reading will be about 415 volts.





.............. Phil
 
C

C3

Jan 1, 1970
0
This isn't directly related to your question, but I have also noticed
flicker on a number of monitors in apparently good order.

Could this simply be caused by the flickering of the fluorescent backlight?

cheers,

C3
 
N

Newsy

Jan 1, 1970
0
TT said:
I am having a problem with a VGA LCD display device when powered from a
different AC power circuit to the video signal source (PC).

If both the LCD monitor and PC are plugged into the same power point,
everything works fine. The problem arises when I power the LCD from a
different power point on the other side of a warehouse. When powered from
different circuits, the LCD flickers or waves/pulses to what looks like a
50Hz type flicker.

I am using a VGA splitter to boost the video signal with a 30M VGA cable to
get across the warehouse floor. I am confident that this isn't what is
causing the problem because I have tried connecting the LCD directly to the
PC through a short 2M VGA cable and run an extension cord across to the
power point on the other side of the room to try and eliminate the cause. In
this case, the flicker is still apparent.

I have also tried a CRT monitor which exhibits the same problems. Also, if I
power PC and LCD together at either side using the same power point, there
is no problem, so I don't think it's a power problem at one particular
point.

Has anyone solved a similar problem before or have any ideas what might be
causing the problem? Thanks.

Probably the easiest way to fix it is to run a power cable along with the
VGA cable and power the screen from the same power point as the PC. You may
have to ensure the power and VGA cables are separated by 30cm or more.

Rod
 
M

Mike

Jan 1, 1970
0
Beat freq, sync source,

up your refresh rate or lower it as LCD does it by-itself
anyway,

mike
 
R

Roger Lascelles

Jan 1, 1970
0
If the LCD monitor is earthed, you may have an earth loop - you can have
substantial current flowing between the earths of two power points.

If the LCD monitor is powered by a "brick" with only a 2 core mains lead,
then an earth loop isn't the problem.

If the LCD monitor does have an earth, then you can disconnect it via a
short extension lead with disconnected earth just to see if that cures the
problem. If it does cure the problem and you need the earth for safety,
then you can use an isolation transformer to give the the same safety as an
earth.

Someone else suggested running a mains lead along the same path as the
video - this might work too.

Generally it is not possible to pipe unbalanced video or audio all around a
building and plug it into earthed equipment along the way. Ultimately you
need isolation via transformer or opto coupling.

Other possiblilities are -

- don't use a monitor, instead put a PC at the other end connected by a LAN.
Of course this changes your software setup and may not be possible. LANs
can handle earth loops because they are transformer / opto isolated.

- use a video transmitter. May be OK if your PC has a TV output which can
plug into the transmitter. You may have to use low resolution in order to
read text.

- Look at http://www.microgram.com.au/ . Give them a ring and tell them
about your problem. They have the sorts of gadgets you may need.


Roger
 
P

Patrick Dunford

Jan 1, 1970
0
TT
I am having a problem with a VGA LCD display device when powered from a
different AC power circuit to the video signal source (PC).

If both the LCD monitor and PC are plugged into the same power point,
everything works fine. The problem arises when I power the LCD from a
different power point on the other side of a warehouse. When powered from
different circuits, the LCD flickers or waves/pulses to what looks like a
50Hz type flicker.

Could be 50 Hz hum = earth loop, very common in audio, it can also affect
video and computer gear
I am using a VGA splitter to boost the video signal with a 30M VGA cable to
get across the warehouse floor. I am confident that this isn't what is
causing the problem because I have tried connecting the LCD directly to the
PC through a short 2M VGA cable and run an extension cord across to the
power point on the other side of the room to try and eliminate the cause. In
this case, the flicker is still apparent.

I have also tried a CRT monitor which exhibits the same problems. Also, if I
power PC and LCD together at either side using the same power point, there
is no problem, so I don't think it's a power problem at one particular
point.

Has anyone solved a similar problem before or have any ideas what might be
causing the problem? Thanks.

Try an isolating transformer
 
P

Patrick Dunford

Jan 1, 1970
0
BOB URZ
Sounds like a ground loop. Short of powering them off of the same
ac power, there are a couple things you could do.
One is use one of the VGA to cat 5 convertors and run cat 5 to the remote
monitor. Some of these will isolate the signal.
The other is a video isolator. Extron makes them, but there
BNC in and out. WIth a little searching, you may find a distribution
and with isolation for a HD15. You need to float the ground one way
or the other, or make the grounds the same by your method of
AC distribution.

Real video isolators use high frequency transformers, for VGA it would
need to isolate all three colours and maybe a bit more as well?
 
P

Patrick Dunford

Jan 1, 1970
0
Roger Lascelles
If the LCD monitor is earthed, you may have an earth loop - you can have
substantial current flowing between the earths of two power points.

If the LCD monitor is powered by a "brick" with only a 2 core mains lead,
then an earth loop isn't the problem.

If the LCD monitor does have an earth, then you can disconnect it via a
short extension lead with disconnected earth just to see if that cures the
problem. If it does cure the problem and you need the earth for safety,
then you can use an isolation transformer to give the the same safety as an
earth.

Someone else suggested running a mains lead along the same path as the
video - this might work too.

Generally it is not possible to pipe unbalanced video or audio all around a
building and plug it into earthed equipment along the way. Ultimately you
need isolation via transformer or opto coupling.

Other possiblilities are -

- don't use a monitor, instead put a PC at the other end connected by a LAN.
Of course this changes your software setup and may not be possible. LANs
can handle earth loops because they are transformer / opto isolated.

- use a video transmitter. May be OK if your PC has a TV output which can
plug into the transmitter. You may have to use low resolution in order to
read text.

- Look at http://www.microgram.com.au/ . Give them a ring and tell them
about your problem. They have the sorts of gadgets you may need.

- Get another power point put in on the same earth circuit.
 
T

TT

Jan 1, 1970
0
Thanks for all the replies. I think the problem is an earth loop as when I
open circuit the earth on one end of the system (either end), it resolves
the flicker. I measure about 200mVac between earths when open. Turning up
the monitor refresh rate does help, but I cannot completely eliminate it as
anything higher than 75Hz refresh is unfortunatly 'out of range' for the
LCD.

A few people have mentioned an isolation transformer, I would like to give
this a try. I thought an isolation transformer only isolated the active and
neutral though, doesn't earth just pass straight through on one of these
things?
 
P

Phil Allison

Jan 1, 1970
0
TT said:
A few people have mentioned an isolation transformer, I would like to give
this a try. I thought an isolation transformer only isolated the active and
neutral though, doesn't earth just pass straight through on one of these
things?



** Often it does - though it is considered OK to lose the earth if an
ISO is in use.




.......... Phil
 
T

TT

Jan 1, 1970
0
Yes, you would have to isolate all. The extron units are 5 channel
RGB and HV. This covers all the signal and sync leads. But it does NOT cover the
data leads. So if you went this route, you would not have auto monitor detect and
would have to preset your monitor in windows. They are also BNC in/out. So cabling
is an issue.

Bob

I found this 'Ground Loop Inhibitor' device at Extron. It has a high density
d-sub 15 pin (VGA) connector for input and output, exactly what I want.
Sounds like it would solve my problem. The box doesn't require any power, so
how does it work? I assume it uses some kind of transformers for isolating
signals.

http://www.extron.com/product/product.asp?id=gli2000&subtype=45&view=desc

Does anyone know who the local distributer for Extron Electronics is in
Australia? I would like to get a price on the GLI 2000 15HD (PN 60-602-01).
 
N

Newsy

Jan 1, 1970
0
TT said:
So

I found this 'Ground Loop Inhibitor' device at Extron. It has a high density
d-sub 15 pin (VGA) connector for input and output, exactly what I want.
Sounds like it would solve my problem. The box doesn't require any power, so
how does it work? I assume it uses some kind of transformers for isolating
signals.

http://www.extron.com/product/product.asp?id=gli2000&subtype=45&view=desc

Does anyone know who the local distributer for Extron Electronics is in
Australia? I would like to get a price on the GLI 2000 15HD (PN
60-602-01).

The local distributor is RGB Integration in Adelaide. However, they will
tell you to go to one of their distributors. I am a distributor, and the
price is $1,850 + GST. It would be easier to run an additional power
circuit off the same circuit as the computer.

Rod
 
T

TT

Jan 1, 1970
0
Newsy said:
in/out. power,
60-602-01).

The local distributor is RGB Integration in Adelaide. However, they will
tell you to go to one of their distributors. I am a distributor, and the
price is $1,850 + GST. It would be easier to run an additional power
circuit off the same circuit as the computer.

Rod

Geesh, I was right when I thought the box looked kind of expensive. Alot of
money for something that 'does not require an external power supply as they
are non-powered' ;)
 
T

TT

Jan 1, 1970
0
Bob Urz said:
Is there no keyboard with the computer on the long end?
If its a totally case isolated device, you could use a small mains
isolation transformer and float the ground to the monitor.

Bob

Unfortunatly the display device is mounted in a metal cabinet that is
earthed for other reasons in my case. (ie. the LCD chassis bolts directly
onto the earthed metal cabinet). Would it be electrically legal and more
importantly dangerous to float the computer end with an isolation
transformer? The computer has a metal case.
 
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