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home>>Tech Tips>>Tech Tip #10
Perfect Geometry and No Banding on a Marquee 8500
This Tech Tip is provided courtesy of Gregor and Terry from the AV Science Forum Website
Originally posted by Gregor
Terry Ferentinos (aka Chuchuf) was making a swing through middle Tennessee this weekend and agreed to stop by and see if he could tweak a little more out of my Marquee 8500. First of all, Terry is a great guy. He knows his stuff and I highly recommend him if you need some help. We did a ground up physical setup on the projector. I had managed to do decent job myself, but had not perfectly centered the rasters and my tow-in was little off as well. Once we got everything positioned correctly, Terry bounced around between astigmatism, physical focus and electronic focus. When he was done I had a much more precise focus overall and the spot beams were much tighter and noticeably more circular.
Then came the fun part - geometry! I have always had a problem with getting a good geometry on this projector without causing banding. Sure enough the first time through Terry set up a nice clean Cartesian grid using the green convergence in the service menu and when we switched to the white field -- bingo there was a big dark band right across the center of the screen! So we went back tried it again, but this time after every small change we checked the white field (rather than waiting until we were finished). Here is what we found. Be very careful with the bow control - even a little adjustment will cause banding. Point controls (called random access in the 8500) are a little less sensitive - but if we used too much bands would appear at and down the screen. The interpolated green convergence on the other hand does not seem to cause banding and you crank this in with near impunity. So here is the procedure that Terry and I came up with to get good geometry without banding - I am sure Terry will chime in if I get this wrong. :)
1) Reset everything (press 0 when in the green convergence service menu).
2) Switching back and forth to white field (actually green field in this case), use the bow control to ELIMINATE any banding - then do not touch it again!
3) Save the convergence frequently as you move through the sequences below - always checking first to make sure that no banding has occurred.
4) Make small adjustments with keystone and pin to achieve a symmetrical (but not necessarily flat) geometry. Check and make sure no banding has occurred.
5) Flatten out the geometry using the interpolated green convergence. This option steps through the zones in a pre-determined sequence so you may need go through the process multiple times - you can also back up to a previous zone by pressing "*" . You should be able to get very close to perfectly flat using just the interpolated option.
6) If need be, go into the random access and touch up a little - but be careful and check the green field frequently as you can introduce banding using the random access mode.
We ended up with a near perfect geometry and no banding - first time ever on my machine. We then did a blue/red convergence and then Terry tweaked the color balance - raising the temp slightly. After Terry left I watched several of my standard disks and I must say the projector has never looked better.
(much thanks to Gregor and Terry for sharing this with us)
Tim at E-Tech Systems Phoenix
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