Magnetic interference or broken monitor (Makvision M3129)?

[emuola]

My previously "almost finished" cabinet project seems to have setbacks after another... I noticed a while ago that there are two "color areas" (purple and green) if the monitor displays something completely white (in this case Notepad in windows).

Here's an image:



As you can see the purple "area" is on the right and the greenish one on the left. I then realised that this looks like magnetic interference. There are two speakers above the display (~35 cm away) and a subwoofer below the right corner of the monitor (~35 cm away). I scavenged a few magnets from old speaker elements and if I put a magnet against the magnet of the sub the purple area (the one right above the sub) completely disappears  Unfortunately I cannot understand where the other area comes from  I tried removing the speakers above the monitor, but the result is the same. There's absolutely nothing in the cab that could cause the interference if you ask me. What could be the reason?

I'm starting to fear the monitor is somehow "broken". Sending the beast back to UK (~3000 km) is something I don't even want to think about...

[rCadeGaming]

Hard drives have strong magnets in them, is there one close?  Do you have a degaussing coil?

[emuola]

Hard drives have strong magnets in them, is there one close?  Do you have a degaussing coil?

Actually there's one... I tried to remove the hd and tried to put it really close the monitor (front side almost against the tube), but it did not cause any interference. So I guess it's not the one to blame. I also tried with a magnet and it clearly made something looking just like my picture. The monitor has "automatic degauss" when it's powered on,I don't have a degaus coil, but I'm not really sure what you mean by that.  It usually takes a few minutes after power on to develop the symptoms (because it's been degaussed on power on).

[rCadeGaming]

It's a handheld coil that allows you to degauss manually at any time.  If the automatic degaussing takes care of it but then it comes back, sounds like you just need to remove the route cause.  Have you tried completely removing the sub, or the whole computer?  Anything else that could be making an electrical field?  Big power supply?  Audio amp?  I'd just remove things one by one and see what changes.

[mamenewb100]

This seems to be a common issue with Makvisions. I have a Makvision 2929D and it does the same thing. It is hardly noticeable when playing regular games but as soon as you browse windows with a white background it leaves purpleish marks. Sending it back would probably be a wasted effort unless you get a different make but even then there is no guarantee. There could be other mysterious causes for it but noone has found out yet that I know of.

[MonMotha]

Does it only do it on bright colors (especially white) and go away once you remove the bright spot?

If so, it's probably because these monitors ship CRANKED.  They're operating way beyond the limits of what the tube is designed to actually handle.  The tube is actually being driven so hard that it heats up and deforms the shadow mask (doming), which causes purity issues (wrong colors).  Removing the bright signal allows the monitor to cool down, and it goes away.

Solution is to turn down contrast.  The monitor will be dimmer, but it'll be correct (and not frying itself and causing burn-in prematurely).

[mamenewb100]

Solution is to turn down contrast.  The monitor will be dimmer, but it'll be correct (and not frying itself and causing burn-in prematurely).

I've tried this and it does make it not as bad but does not get rid of it completely. But it's better than doing nothing for sure.

I'll also add that it seems to happen at random sometimes though. I've had a white screen up for an hour before with no trace of the brown/purple spot and other times it comes up everytime there is white.

[emuola]

Thanks guys for the replies  I guess my Makvision is like the others... I noticed yesterday that when WinXP screen saver kicks in (after Notepad has been running for a while with the purple spots) and after hitting the keyboard the notepad is pure white, no traced of purple spots  So, the screen somehow "resets" itself after there's something else than just white. If it would be magnetic interference the spots should be there after screen saver also, right?

I'll turn down the  contrast, thanks for the tip How about the brightness?

[rCadeGaming]

Sounds like this confirms Monmotha's theory.  Putting out a pure white signal causes to it to heat up after a period of time, then the dark screen saver allows it to cool down.  And yes, if was magnetic interference it wouldn't have changed after the screen saver.

Very interesting.  I hadn't heard of this, but it makes perfect sense.

[emuola]

Sounds like this confirms Monmotha's theory.  Putting out a pure white signal causes to it to heat up after a period of time, then the dark screen saver allows it to cool down.  And yes, if was magnetic interference it wouldn't have changed after the screen saver.

Very interesting.  I hadn't heard of this, but it makes perfect sense.

Yes, sounds reasonable even with my very incompete understanding of crt:s  I'll test with lower level of contrast - I guess it's just a compromise between the monitor "brightness" and the so called "artifacts". At least I tore down the whole cabinet yesterday evening, so every screw/bolt has been checked now  I'll start reassembling tonight 

[MonMotha]

Brightness is much more easily set.  Bring up a gray ramp (0-100%) and adjust it so that the bottom ~10% is identically and completely black.

Contrary to what its name may lead you to believe, "brightness" doesn't actually adjust how bright the screen is.  It actually adjusts the so-called "black level", which is the signal level at which there's insufficient drive to the tube to make it do anything i.e. it's totally black.  This can be set "correctly".

Contrast is a bit more fudgey.  Basically, set it so that it's "bright enough for your taste" without blooming.  Causing doming like you seem to be experiencing is pretty extreme.  I'd expect it to be exhibiting other artifacts first.  Given how often people seem to experience this problem on these monitors, I have to wonder if they have crummy shadow masks in their tubes that easily deform or absorb lots of energy and heat up unusually fast.  Regardless, set brightness "correctly", then just keep turning down contrast until it doesn't do this.

[emuola]

Brightness is much more easily set.  Bring up a gray ramp (0-100%) and adjust it so that the bottom ~10% is identically and completely black.

Contrary to what its name may lead you to believe, "brightness" doesn't actually adjust how bright the screen is.  It actually adjusts the so-called "black level", which is the signal level at which there's insufficient drive to the tube to make it do anything i.e. it's totally black.  This can be set "correctly".

Contrast is a bit more fudgey.  Basically, set it so that it's "bright enough for your taste" without blooming.  Causing doming like you seem to be experiencing is pretty extreme.  I'd expect it to be exhibiting other artifacts first.  Given how often people seem to experience this problem on these monitors, I have to wonder if they have crummy shadow masks in their tubes that easily deform or absorb lots of energy and heat up unusually fast.  Regardless, set brightness "correctly", then just keep turning down contrast until it doesn't do this.

Set the brightness according to the ramp and lowered the contrast -> looks much better. The "artifacts" are not noticeable anymore. Thanks to all involved