RPCRT Overscan Reduction - SHIMMING

Thanks for sharing. I just did this mod to my pioneer and have some question. I believe I have some geometery problems just outside the boundries of visable space but I believe they existed before I did this. There is a lot of geometery work to do, more than I thought but I'm getting the hang of it now. I have some colors that have really bent lines at the outer edges. At first I decided to just resize the image larger to avoid the problems but that appears counter to my objectives and I can't get convergence at the edges.

I was wondering, would it be wise to bring in the size enough to see the bent lines on the outer bounds in attempt to get them as straight as possible first (doing each color independent), then increasing the size to about 3% overscan, then doing the color convergence again?

Any other ideas, I will post some picture when I can

Thanks

Nice thread, superleo!

Have a "bachellor's week" coming up (wife heading out of town for a work conference). Might be the best time to tackle the shimming process, as well as any other internal modding I might shoot for.

If I can nail it along the lines you appear to have done (2.5 % o'scan), I will be stoked.

I the circle hatch and the screen shot I see a bit of green. This is a similar problem I'm having but it's red and I think it's caused by the red convergence on this outer edge.

Not to speak for leo, but I do think that his shots were of the "quick & dirty" variety - taken before final touchups.

However, still want to see how it turns out in the end & if leo does address the green stuff you mention. I have seen similar "green edges" after o'scan redux (not the shim variety) before.

How much of a difference do you think the black fabric made?

Well, the inside of my case is black plastic. I'm not sure how light absorbent it is however.

Awesome expose, Superleo!

I just donned my mad scientist cap again yesterday - it said, "I want you, boy!" and I had to comply...

So I performed all that was necessary to remedy the fact that my red and blue guns had been absolutey MISERABLY aimed by Mit at the design stage. They were both hitting the screen slightly cross-eyed, meaning that most of the pic was at one edge, with a whole bunch of space at the other. I learned years ago directly from Jim Doolittle that you never let your image go thru your lenses at an angle, they need to shoot straight thru or you get aberration of your image.

I know that this makes the same 9" gun array fit both the 73" and 65" Mit versions, and can't wait to see a 65" version again, to see if it's still THAT much off as what I found on my 73".

Be that as it may, the full potential of my CRT faces was NOT being utilized! There was space there that the image could be expanded out to. Since my CRT faces have no visible wear on them yet - I am VERY sensitive to ANY kind of screenburn, and watch for that like a hawk - including the natural amount that comes from 16x9 images being shown on 4x3 guns, I knew I could expand my pic to take in that previously unused face area and get away with it, maximizing the potential of my display. Which is what the shimming op is all about. Reducing the o'scan can be done in the sm, but doesn't increase the amount of the CRT phosphor face being utilized. The shimming op does, which is what gives us the added spaciousness in our images, like the difference between 7" guns and 9" guns aimed at the same size screen. I had optimized it for the most part, but after examining it last week and finding the above results, I realized that it had not been maximized yet.

So I loosened the inner screws on each of the outer guns and released just the outsides of my red and blue guns enough to let them fall back a little bit, angling them correctly, then increased the size on all 3 of the CRT faces, since a whole bunch was now available, that had not been available before.

This also involved adding another thickness of shim to my already triple-pack, for a 4'ple pack. My shim distance is now a full 3", up from the former 2.25", of multiple 3/4" thicknesses. If I had known then what I know now, I woulda used 2 thicknesses of 2x4 on each corner and been done with it.

I will send in pix soon.


For CRT RPTV, unless you can actually do the shimming method, I would not recommend even trying to go below 4%. You might squeak by with 3.5%, but the conv feathering at the edges on your hor lines gets pretty bad after that. With the shimming I have done on mine I can now go to just under 3%, but since you have to have your hor and vert be ID, the entire size is limited by the shortest one.

I have also found that the HD DVE o'scan pattern is slight off. With all edges at exactly the same measure, if you actually take a yardstick to your image on the screen, you'll find that the circle is actually a vertical oval, by about 3/8" on a 73". I therefore have decided to go for 3% at my sides, and 2.5% at t/b, which makes the circle go back to being a true circle.

Perhaps my Mit is deranged, but this is also from the rectangles in my set's internal grid, so I don't think the display is the issue. I think it's the test pattern. We all know his o'scan pattern on the original SD version of VE was worthless for 16x9 geometry, so it's really no big surprise for this version to be slightly this way also. The SD version of VE was completely worthless. The HD version of DVE is almost perfect, with just this slight offness.

If you try to go any lower on CRT RPTV tech, you begin exposing the fact that on one side some of the lines go up while on the other side the same lines go down, as they leave the screen. In this event, the feathering can only be averaged between them, not remedied. If both sides go up and you have a Mit or Pio, you can use the invisible side columns to get it right. But if one goes up while the other goes down, averaging is the only answer.

If that makes 2.35:1 movies with black t/b bars show conv error at the extreme sides, you can mitigate that at those areas by moving the error in towards the middle a bit. This makes the area closer to the center a bit mulchier for 3"-4" in from the side edges, but does not overshow the aberration at the far edges as much.

This kind of thing is why they did overscan in the first place - to hide it.


More later -


Mr Bob

I'll have to do this to my Panasonic one day, including an optics cleaning and maybe even a full calibration by a certain Mr. Don't dump your CRT RPTV. I'll start collecting every penny I find...

Doing a shimming isn't that hard is it?

Superleo, very nicely done report!!!, and thanks for sharing.


Mr Bob, it just amazes me how you are able to refine these tweaks the way you do, and look for improvements! This is just like the programs monster cars/ trucks, and Pimp my Ride!


I have a question about shimming again, but still havent the nerve to try it.
Can you run out of optical focus with these lens with the shimming? Or you would be beyond 0% overscan before that happens?

Thanks! Come on over and watch my pimped out display sometime! Love to have you observe it and write in about it.




On my 73" Mit my shimming difference is only 3", on a folded throw distance of maybe 5'. It's not going to upset ANY optical focusing, you won't come anywhere near to running out of room to move on your lens barrels. I changed my lenses when refocusing by maybe a MAX of half an inch, edge to edge, barrel to turret, on the turning of the lenses, which probably has at least 2 inches of total turning capacity.

I have never come close to running out.


b

You have to be ready for anything. On one I did the whole thing only to find that the aging footprint was too great and the difference in centering between the 2 sources too great, resulting in too much showing in too many places. It resulted in having to dismantle the whole thing and put it right back where I started.

It's not rocket science, but it does take a WHOLE lot of tenacity!


b

Feathering, I think that is exactly the problem I'm seeing with my Pioneer. I have invisable columns on the top and right side but not the bottom and left. Also, I may have to live with 6%. After the shimming mod, assuming the geometery was correct befor that when I change the horizontal size I need to change the vertical size proportionately? Can I just calculate the percentages and work out the fine convergence afterwards to get better convergence?

The right side affects both the right and left. But in a crazy kind of way. I have a system that I discovered that allows it to be dialed in just right, but it took me years to figure out...


b