CurtPalme.com Home Theater Forum

JustGreg · Joined: 07 Mar 2006 Posts: 3098 Location: Kenosha, WI

I'm really digging into my HT right now (M8500) and wanted to get a question concerning keystoning out of the way before going past a point I shouldn't have. I don't think I'm running it at an 'acceptable' number. (~90)

Following the installation guide way back when I ceiling mounted the pj with the (inverted) base bubble level; which resulted in the built in 10 degress of downward pitch. The screen is plumb.
The base isn't quite per the manual in regards to base to screen top edge. (think inverted from what the manuals illustrations show) I simply don't have the room to raise the screen, and don't want to lower the pj because doing so would obstruct viewing from the riser seats. Without running down to measure I'd say the tube centers are about 6-8 inches below the top of the screen edge.

It's a 96 model and has unknown hours on the chassis (can't trust the clock's anyway) and hasn't been recapped but all socketed chips and connectors (boards and cables) were recently cleaned with Caigs.

That said, I've always had to run the keystone at ~90 for good symetry. That seems crazily excessive to me. Does this indicate nothing more than my less than perfect physical arrangement(s) or is it indicative of something else that needs to be addressed before I break my neck and back hunched under it? I've swapped in (and back out) everything but the Stig Amp, Vertical Board, Convergence boards, PS's, motherboard and backplane....alot I know but that 90-ish number remains static.

This is especially important now because before ordering the new red tube I noticed the blobs became tighter at the top than the bottom. I never had (or noticed) that 'problem' before something went belly up a month ago or so. No pop, snap, power loss, or anything I could associate with the sudden change. It's definately noticeable with small text or opaque text boxes such as found in PS Home (more so in the bowling alley with the high gloss lanes and the chat window open).

To close my ramblings; when I perform a full reinit the grid lines are definately NOT what the illustrations look like in the manual, eg, nice square grids. All three tubes show lines warped up or down (but not wavy) with an overall need for serious keystone to flatten the grid but major .

When these things (pj's) are new, are the grid lines straight vertical and horizontal or is it normal for one or more colors to display lines that dip down? I know how to adjust horizontal and vertical by rotating the yoke but the lines always require more convergence 'pull in' than I'd like. This after a good magnetics alignment and overlay (in the center) first.

I didn't mean for this to be so long but a couple hours of searching the web was no roadmap. Wink

I'm commited (or should be) to getting this setup as perfect as I can without bringing in an ISF rescue squad.

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

I Greg, the 90 should be about right taking into consideration your description of your set up. My Blend has keystone at about 14 for both PJ's.

When initializing a set it resets the geometry so the grids will be bowed on all sides and the degree to which they are depends on physical set up.
I think all is ok on your set up. The one thing that would help is to lower your PJ but you can not do that due to the last row viewing. I have the same issue.

Athanasios

jkruger · Joined: 24 Oct 2007 Posts: 2435 Location: Carlsbad, CA

Mounting your screen higher sounds like the only way to get less keystone. How high are your ceilings? The center of my screen is at 75" from the floor and the center of the lenses are at 85". I have the projector (1209s) angled slightly down in front so the rasters remain as rectangular as possible. I use very little keystone. My projector is too close (90") to the screen at this time, but when I move it back to 110" there should be nearly zero keystone used. My seating is at 200" and 260" from the screen. I'm considering moving it closer.

JustGreg · Joined: 07 Mar 2006 Posts: 3098 Location: Kenosha, WI

Info overload today but I asked for it! Laughing

Only day off so I'm trying to gather as much (printed) info as possible and preparing a (time) efficient procedure I can follow with what little is left of my brain when I get home from work at 2am.

So...it's as I thought. The angle of the dangle can't be wrangled. I MIGHT be able to raise the screen a couple inches and drop the pj a couple inches (short people to the back please! Mr. Green

). That should alleviate some of the keystone stress. I might even be able to add a few degrees up to the screen but I'd rather not aim the cone at the ceiling if it can be helped. The screen part is easy...the pj....not so much.

Tim has said repeatedly over the years that the Marquee's electronics can handle quite a bit more positive numbers than we give them credit for. That may be the case on a new set but as they get a decade or so under their belt I suspect drifting becomes an issue.

I'm starting too many threads with off topic questions mixed in, and I apologize for that, but it just seems more efficient given my limited time...and they ARE all related to geometry and convergence.... more or less. Rolling Eyes

JustGreg · Joined: 07 Mar 2006 Posts: 3098 Location: Kenosha, WI

stefuel · Posted: Wed Apr 07, 2010 10:15 pm Post subject:

Well if you can't move the screen up and you don't wish to move the projector down you can pull the bottom of the screen out so that the angle of the face of the screen is 90 degrees to the base of the projector when it is tilted down to strike the screen center. That will cut your keysone for sure. If you are using a low gain screen you shouldn't see a problem.