Purposefull screen burn in.

[protokatie]

I am attempting to do something that almost anyone with a CRT would try to avoid. I have a CRT HDtv and am using a cheap VGA to NTSC adapter that has the green levels too high. I cannot adjust anything that fixes the problem (why do no screens have RGB level adjustments???!) and am looking into displaying a strict green screen on the display for an extended period of time to "dull" the green phosphors. Yes, I know this is not the best option, but this is more or less a throw away screen and this adapter is prolly going to be the last thing attached to it.

Any ideas on the amount of time I should be doing this green burn in? Any potential problems I may run into when doing this? A good way to test for when green is getting close to the other phosphor levels? (When the screen is bllack, I can see the green glowing a bit). Ideas?

[ark_ader]

I do not think this would help, but I had an old CBM 1902A RGB monitor that I used for a few arcade boards.  The monitor was displaying too much red and created a cast over the entire screen.  I got a big magnet and circled the screen and it cleared it up. With regard to screen burn in I remember the MAME team creating a graphic image to simulate burn in.  Maybe you can look at that direction to compensate.

[MonMotha]

There are often adjustments inside or in a hidden "service menu" that would probably fix what you describe.

However, since you have access to the RGB input, you can fix this.  Just chuck a resistor in-line with the green signal.  The value you need depends on how much attenuation you want and the input impedance of the converter device.  If it's 75ohm (broadcast and PC standard), try about a 10 ohm resistor.  If it's 1k (reasonably common "high" impedance), try about 100 ohms or so.

Many of those converters also have adjustment pots on them.  You could just turn the green down.

Now, I question why you're using a converter?  Most HDTVs seem to have a PC compatible input on them (either analog RGB or DVI).

[Haze]

I do not think this would help, but I had an old CBM 1902A RGB monitor that I used for a few arcade boards.  The monitor was displaying too much red and created a cast over the entire screen.  I got a big magnet and circled the screen and it cleared it up. With regard to screen burn in I remember the MAME team creating a graphic image to simulate burn in.  Maybe you can look at that direction to compensate.

That's just a silly novelty, it won't help, and it has no place in MAME IMHO.

[MonMotha]

FYI, it sounds like you may have a cut-off control mis-setting rather than gain.  Signal attenuation won't help as much with that as a gain setting error, but it'll help some.  If you can, the service manual for your TV will likely let you adjust this (or it will be an analog adjustment inside the set).  Intentionally burning the screen won't help a lot (it'll make the bright greens dimmer, but it won't help much with the low level green on what should be black).

[FrizzleFried]

Uh,  has anyone ever seen "color" burn-in?  Me neither.   Your problem is with the electronics,  not the tube.  If you burn the tube,  all colors will be affected... not just green.  You may lower the intensity of the green (maybe...and somewhat) but the rest of the colors will be dimmer as well.

Is there no neckboard adjustments?

[MonMotha]

Burn-in is largely due to phosphor degradation.  This happens as they are "used".  You can, in fact, burn certain colors.  This is somewhat typical, in fact.  Go find an old Daytona or something that had the yellow "LINK SYSTEM" graphic up 75%+ of the time it was on.  A white screen will show that with the opposite colors pronounced (so lots of blue, since the graphic was yellow which uses red and green).

[protokatie]

Well, a coworker came up with a simple fix for the green levels being too high, adjusting the gamma in the NVIDIA control panel. I brought green down to .9 and the color is perfect now!
The green level problem was actually caused by the VGA to NTSC adapter (and comments I have read on this particular device indicate this is a prob with all of them).
Thanks for the advice anyways.

[mvsfan]

Well, a coworker came up with a simple fix for the green levels being too high, adjusting the gamma in the NVIDIA control panel. I brought green down to .9 and the color is perfect now!
The green level problem was actually caused by the VGA to NTSC adapter (and comments I have read on this particular device indicate this is a prob with all of them).
Thanks for the advice anyways.

I think you may have just solved my problem TOO.

Ive got a second cabinet that i havent yet converted to mame. The screen is very dark and i have determined that it is the picture tube. It wont display a jamma board at all theirs no more adjusting for brightness.

Never really thought about the fact that i could just adjust the pc brightness after ive installed the PC. its a real Duh on my part.

probably wouldnt fix the problem though since the problem is in the monitor itself, right?

[protokatie]

Its worth a shot. A friend of mine had an old CRT that was too dark (it was old) and cranking up the gamma really helped it out. Prolly will shorten the life of the display, but atleast it was usable again.

[MonMotha]

Gamma isn't really brightness or contrast.  It's actually a 3rd parameter that attempts to make it so that equal levels of change in the video signal cause equal levels of change in the perceived intensity of the picture.  However, turning gamma up will make the picture look brighter, and I guess if it looks fine to you, have at.

If the BRIGHTNESS (actually black level) setting can't be turned up high enough (that is, dark grays are still fully black), you may just need to bump the screen control (usually on the flyback) up a tad.  They can drift with time.  This can also compensate a little for tube aging.  Some monitors also have a "sub brightness" setting that is very coarse.  There are also often "cut-off" or "bias" controls on the neckboard for each color.  If the CONTRAST setting (actually "brightness" or "intensity") can't be turned up high enough, then you may be able to find a "sub contrast" control somewhere else on the monitor or crank the individual color gains up (often on the neckboard).  These controls are usually very coarse and have large adjustment range.  You may also have luck having a local monitor/TV shop "rejuvinate" the tube if it has degraded.  You should always be able to get some sort of picture out of even a weak CRT.  A very weak CRT will just start to "bloom" quickly before attaining acceptable intensity of the output.  If you can't get a picture at all, then you have either a connection or adjustment issue most likely (or the tube is totally i.e. mechanically broken).