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Shooter
20-02-2003, 01:18 PM
While all you experts are discussing monitors I would like you to give so thought to my problem and would appreciate any help.
I have a CTX model VL700 - 17inch monitor (made in Thailand) which has a permanent shimmer to the edge of the picture. It can be seen best when there is a light background to the picture such as this window or in Word with a document open. This problem has been there from purchase. The supplier has replaced the monitor 3 times and had them 'checked out' and cannot find any fault. I have increased the refresh rate to 85 hertz which is the largest that can be used for this monitor according to the control panel display. This has helped some but the shimmer is still there!!
Some have said it may be power interferance or could it be something in my computer? I have a PIII 450

Cheers
Shooter

OldEric
20-02-2003, 04:09 PM
More info needed.

1. Is the shimmer on the left hand side of the screen?

2. Is it a thin vertical line and if so would you describe it as a vertical rope? Maybe 3-5 mm wide?

Can you move it off screen by increasing the monitor picture width?

I assume each of the 3 monitors gave the same symptoms?

OldEric

Billy T
20-02-2003, 04:35 PM
Hi Shooter

After three monitors it is an odds-on bet that the monitor is not the problem. If it looks like physical movement on screen it could be external electromagnetic interference and the first thing to check is that you haven't introduced any sources close to the LHS of your screen. Any mains powered small appliance (clock, radio, tape,etc) will have either a built in transformer or use a plug pack. If such a device is anywhere closer then 10cm from the side or rear of your monitor, interference is a possibility. I have seen HP printer plug packs causing this when they were tucked out of the way behind the mnitor. Small UPS's are also a common cultprit.

Here's five things to try:

1) Reset the screen refresh rate to 56 or 60 Hz and see if the effect changes/gets worse.

2) If it does, try clearing around the monitor to remove any sources as per my initial comments.

3) Physically shift the computer & monitor into another room and see if the problem continues.

4) Try the monitor on another computer to eliminate video cards or any other wierd driver problem.

5) Go outside and see if there are any HV powerlines running over your house, or if you live in an older area, is your house close to the street and the street powerlines?

Perhaps number 5 should be first on the list, as the last person to post this problem found that that was the cause.

If none of the above apply and the effect survives move to other rooms etc, we'll have to get down and dirty on it because there will be something very strange indeed going on. If you decide it is an external effect let us know and I'll post an email address to establish contact so that we can talk. I can give you professional advice (free) on how to pursue the problem further.

Cheers

Billy 8-{)

Elephant
20-02-2003, 05:05 PM
Very often unshielded speakers cause this one. Just try moving the speakers further from the monitor for a start. It is not the only solution but it's worth a try.

Billy T
20-02-2003, 05:23 PM
Sorry Elephant, powered speakers might possibly cause interference if the power source was inside one of the speaker cabinets but I have never seen such an arrangement myself.

Having said that I recall that the old Philips 15A monitors with built in speakers used to cause image instability at high volume, but I suspect that the mechanism was something other than magnetic fields.

Other than that rare option, speakers are a static magnetic field source and can only produce image discolouration (purity or white uniformity errors, not movement. To cause movement you require an alternating magnetic field as it must interact with the scanning frequency to produce the on-screen effects. For example 50 Hz interference source + 60 Hz scan (refresh rate) produces 10 Hz interference movement on screen.

That speakers cause image movement interference is a very common misunderstanding.

Cheers

Billy 8-{)

ferrer
05-04-2005, 03:51 AM
Hi all,

I have this probelm too. Annoying thing is I have a small design company and so we really need good monitors. I see a high voltage powerline outside. All staff have this issue and I have paid for a years rent. Does any one know of anyway around this issue?

Would be much much appreciated

Tristan

tris(at)firejuice(dot)com

pctek
05-04-2005, 09:52 AM
Actually my fathers shimmer was fixed by INCREASING the Mhz. He ended up using 75hz instead of 60 and it was fine then.

Speedy Gonzales
05-04-2005, 10:24 AM
Sometimes it can happen if the Hertz is too high.

Even tho, it may show 85 or whatever as the maximum screen refresh rate, the monitor you're using may not handle it.

Try lowering the hertz.

godfather
05-04-2005, 11:05 AM
Seems likely (as it affects all monitors) that it is a high external magnetic field, and this could derive from close proximity transmission lines.

CRT monitors are affected by magnetic fields, and changing the refresh rate will change the "shimmer" frequency (by the difference between the refresh rate and 50 Hz, the mains frequency) but will not eliminate it.

Realistically you cannot shield a CRT monitor against it, but moving the monitor to face in a different direction may mitigate some of the effect.

That does indicate a high level of field though, and if it were me I would be getting it professionally measured. You are afterall working in it all day.

Graham L
05-04-2005, 01:51 PM
The original case involved multiple monitors of the same make and model. I suspect this one might, too.

Never exclude the possibility of a design fault. Perhaps something designed in the "World" of 60Hz might beat to a different drum in the real world of 50Hz. ;)

ferrer: try a monitor of a different make. It may be less sensitive to external fields, or not have the capability of visible beating. If another make doesn't do this, you might have a case against the original supplier.

apparition
05-04-2005, 05:43 PM
I work in a cube farm and it gets really hot. The problem is that a desktop fan (even a small one) is bad for causing a shimmer (any electric motor is (magnet boosted by copper coil)). Anyway, depending on the strength of the magnetic feild, the effect can happen from quite a distance.

Keeping myself cool affected three monitors

Any magnet will do it, not just electric sources.

Billy T
06-04-2005, 01:17 AM
Realistically you cannot shield a CRT monitor against it, but moving the monitor to face in a different direction may mitigate some of the effect.

Well GF, another rare disagreement! You most certainly can shield monitors against external fields, and I have done so for a number of commercial clients using imported custom built shields. I have shielded monitors up to 21" with great success, even in high field situations like power stations.

My orignal advice at the head of this elderly thread stands though, and it is not "all magnets" that cause shimmer-type interference, it is only electrically powered sources that do this. Static magnetic fields just cause discolouration.

Increasing the refesh rate is not a real answer either because although the interference appears to go away, it is still present but tracking faster than the concious eye can see. Unfortunately the 'subliminal eye' still sees it as a blurry image, causing fatigue and headaches for users. Some users can get away with it though if their eyes have lower than average response time.

The best answer is LCD screens but they don't always suit users of larger CRTs, espcially in the graphics field.

Cheers

Billy 8-{)

godfather
06-04-2005, 09:43 AM
The "realistically" qualifier suggests that perhaps they cannot "realistically" afford your fee for doing it...?

Billy T
06-04-2005, 10:04 AM
The "realistically" qualifier suggests that perhaps they cannot "realistically" afford your fee for doing it...?

Point taken GF :horrified , but it is not all that expensive and significantly less than the cost of conversion to large screen LCD. It is more of a sales transaction than a consultancy issue. Certainly enough users found it an economic solution to make it worthwhile holding stocks here in NZ.

The biggest problems are the bulk of the shield, and the need to customise the shield dimensions to minimise that bulk for 20" and 21" monitors. All others fit in standard sizes.

Cheers

Billy 8-{)

communal
18-08-2005, 05:23 PM
You most certainly can shield monitors against external fields, and I have done so for a number of commercial clients using imported custom built shields. I have shielded monitors up to 21" with great success, even in high field situations like power stations.

I have large speakers close to a crt monitor in a tight space, so moving them away is not really an option. Is there a cheap way to sheild them? What can be used?

Billy T
18-08-2005, 05:51 PM
Well, you can shield them but it will not be pretty. In essence you will need some fairly thick steel, 1mm would be about right, and that will have to cover the side of each speaker that is facing the monitor and go about 50-75 mm past the back edge of the speaker enclosure. It can bend around the back if you want to try that.

You can shield inside speaker cabinets, and if they heve exposed ferrite magnets I have seen good results with a semi-circle of heavy gauge metal around the side of the magnet closest to the speaker.

Forget aluminium foil or any other folk-lore remedies, ferrous metal and a fair amount of it is the only effective shielding, unless you go to exotics like mu-metal that will cost you an arm and a leg.

You could try doing several degausses of your monitor as well, that may reduce the problem slightly, but it is not a cure.

Cheers

Billy 8-{)