CurtPalme.com Home Theater Forum

[winny]

After a full weekend of mechanical tweaking and hours of convergence, picture quality is better but I'm still confused about G2 and greyscale. I realized something was wrong when raster setup in the installation menu didn't show anything and once set up, everything near black showed up as black. Contrast was to some extent more than I bargained for when I went for CRT in the first place - black OR white.

Disregard the convergence, smudge on the lens, crappy mobile camera and backscatter from the room but here is what it looked like:



So, I placed jumpers on the neckboards, showed a 0-20 IRE picture with black background, set the brightness to 10, contrast to 0 and turned the pot way up until I saw the raster. I was told to aim for just below visible but the pot is single turn and the gain was huge so it was a matter of a single degree in the end and my arms are not long enough with the projector hanging to look into the tube and turn the pot at the same time. Ended up with just above visible raster on all three.

Dark grey became better but at the cost of the raster being more visible at about 45 brightness and 75 contrast. A better compromise than before but this will need more work. I'll try to take a picture of it tonight.

I tried to plow though Kals greyscale for dummies but it was very dependent on external CMS and not so much about CRTs and I'm far from trying to get the last bit of picture quality. More first adjustments after setting it up...

I run it though a DVDO VP50 Pro which has limited CMS. Projector is a BG1209/2. Source is HTPC.

Where to start?

[cmjohnson]

I'll just tell you that after performing a "proper greyscale calibration", I always have to make a few tweaks to the settings to get it to look right. "As calibrated", I also get issues with a visible raster so don't worry about it too much.

Sometimes, you're just fighting the built-in gamma correction curves in your PJ's video amplifier chain. While that CAN be ironed out, to some extent, particularly if you're using a PC for your video source and can create multi-point greyscale calibration curves to "fix" the greyscale curves in your projector, the best approach may be to get the projector's circuits modified to correct gamma. I'm not very familiar with the Barco segment of the CRT modding hobby, but I am pretty sure that somebody here knows something about it and can point you to a reputable modder who can perform the gamma circuit mods that you will benefit from.

[Curt Palme]

I do this with the 1209 projector, which does not have an easy setup for G2/grayscale.

1) Set brightness and contrast to 55 each
2) go into the 'pix adjust' menu, and set all gains and cutoffs to 50
3) Short all 3 jumpers out on the neck boards
4) Using a stepped gray scale from an AVIA or similar disc, set each G2 so that the 0IRE step is _just_ lit on the tube face, not bright enough to show on the screen.
5) take off the shorting jumpers on the CRT neck boards
6) Observe the gray scale. If all tubes are in good shape, and of roughly equal emission, your gray scale should be good. If not, then adjust the gain settings in the pix adjust menu for the bright (80-100IRE) areas, and the cutoff for the 0-30 IRE areas.

[Curt Palme]

I do this with the 1209 projector, which does not have an easy setup for G2/grayscale.

1) Set brightness and contrast to 55 each
2) go into the 'pix adjust' menu, and set all gains and cutoffs to 50
3) Short all 3 jumpers out on the neck boards
4) Using a stepped gray scale from an AVIA or similar disc, set each G2 so that the 0IRE step is _just_ lit on the tube face, not bright enough to show on the screen.
5) take off the shorting jumpers on the CRT neck boards
6) Observe the gray scale. If all tubes are in good shape, and of roughly equal emission, your gray scale should be good. If not, then adjust the gain settings in the pix adjust menu for the bright (80-100IRE) areas, and the cutoff for the 0-30 IRE areas.

[redfox001]

For calibration of CRT you need the old version.
https://www.curtpalme.com/forum_archived/viewtopic.php@t=10457.html

[winny]

Curt,

That's certainly a bit different from the procedure I used and informative. Thank you!
I'll give it a try when I can find the time for it and possibly a friend to look into the tube while I'm turning the pot since and not step-by-step iteration since that part was highly time consuming.

redfox001,

I did plow though it, and while it did go into depth about measurement and external CMS, it didn't say much about the basic settings you need to do before applying external compensation.
EDIT: The old version was far more CRT-oriented than the current one. I missed that part and will read this one instead.

[redfox001]

Think you went through the new version. The old version has little on CMS.

[stridsvognen]

The DVDO VP50pro dont have any CMS at all, it just have the normal brightness, contrast and gamma adjustment.