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XG135 Convergence

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Tip by Mark Rejhon:  (8/30/99) Convergence HOWTO - NEC / Runco projectors
[MARCH 2000 ADDENDUM: For HTPC users, it is preferable to use equivalent test patterns using DisplayMate computer software or using bitmap test patterns instead of using the projector's built-in test patterns.]

"Yes, a howto would be nice. But in the meaintime, remember this mantra when doing convergence: CENTRE first, EDGES next, CORNERS last! And avoid zone/point convergence until the very last step (even though it's tempting to do it sooner). Before adjusting, leave your projector for half an hour to warm up before you begin to do the mechanical convergence/focus.

Without further ado, here's my personally recommended steps for NEC and Runco projectors. I'm not an ISF technician, but I do consider myself to be more technology-literate than the average Home Theater user:

Make sure electronic static convergence is set to 0 for all CRT's before mechanical convergence. First, I do the mechanical convergence and mechanical focussing, as well as the electronic focus/astig. I won't bother going into detail about this, but if you have zone focus/astig, do the center first, edges the next, and corners the last. Do mechanical focus before you do electronic. Do electronic focus before you do astig. I normally start with the green CRT first, then red CRT, then blue CRT. Also, sometimes the astig test pattern is no good - use a DisplayMate computer test pattern (or as a crude measure, the computer mouse arrow pointer as a reference of focussing/astig) ... for more proper astig. I just try to adjust astig left/right until I get the sharpest image in that part of the screen, then I adjust astig up/down until I get an even sharper image in that part of the screen. (Sometimes I repeat these steps twice, to make sure I did not overshoot). After proper adjusting, I can now just about barely see line structure at 1024x768 on my NEC XG135 (8" CRT) when I'm staring few inches from the screen - that's more or less how sharp I've managed to get it.

Secondly, I do the green CRT geometry - it's gonna be your reference CRT when doing red/blue convergence later on. Make sure the green CRT is approximately positioned and sized (use image size and position - don't use static convergence to adjust position of green CRT image at this point). I Use tilt/bow/amplitude/linear/keystone/pincushion to do the best you can, and then use RGB point convergence to make green CRT look corect. Repeat the steps for any further small changes and adjustments you need to do. At this point you DO NOT adjust the green CRT further anymore - you're finished with the green CRT even before you touch the red/blue CRT. So you have to try to get the green CRT visually as geometry perfect as you can at this point, especially with the edges lining the boundaries of the screen properly.

Thirdly, I do the convergence of the red CRT onto the green CRT. (red/green CRTs enabled, blue CRT disabled at this point) I use the fine grid pattern. First, I do static convergence to make the exact middle look correct. Next, I look at the middle of the 4 edges and I do it roughly in this order: static/tilt/amplitude/linearity/bow ... First horizontally, then vertically. Sometimes I have to do "key balance", "linear balance", "linear distortion" to compensate for minor imperfections, you should learn how these adjustments work by experimenting with a spare memory slot in your projector. While doing all these adjustments, I completely ignore the corners for now, while I focus on making the middles of the 4 edges as perfect as I can. I try to make the middle horizontal line (of the grid pattern - the line that divides the screen into a top and bottom half) and the middle vertical line (of the grid pattern - the line that divides the screen into a left and right half) as perfectly converged as I can, converged both horizontally and vertically, by using the grid crosslines as my point of reference during adjustment. (Don't worry about the corners for now) Next, I focus on the corners - I only do edge-specific keystone and edge-specific pincushion adjustments (to tilt and curve the 4 edges of the image individually, one edge at a time). Edge-specific keystone/pincushion doesn't move the middle of the edge, but affects the corner convergence by tilting the edge or curving the edge. No further general geometry adjustments are usually needed at this point when you are converging the corners. Finally, when I am done with the red CRT, I repeat all of these above steps with the blue CRT (red CRT disabled, but with the green/blue CRTs enabled).

Finally, I do point convergence. I start with the red CRT (red/green CRT's enabled, blue CRT disabled). If you've done the geometric adjustments very well like I have, you DON'T need to do zone convergence - only point convergence. (Zone convergence = move many points of the grid at once, Point convergence = move one point of the grid at once). With NEC XG135 CRT projectors, use medium point convergence (coarse normally not necessary) to converge the red CRT as well as you can onto the green CRT. I work convergence in a spiral pattern going outwards from the middle, going from one grid square to the next, converging each one by one - always start in the middle. Ideally, you should do the center first, edges next, and corners last, but going in a spiral pattern pretty closely approximates that and is easier to do. Don't bother doing "fine" convergence (208 point convergence for NEC XG135) since it is a lot of work, unless absolutely necessary - sometimes you come across spots that can only be accessed by "fine" convergence though usually "medium" is usually all you need and will properly converge the whole image most of the time. Next, I repeat these steps and do the blue CRT convergence onto green CRT (with the red CRT disabled). As a general rule of thumb, try not to create more than 15-20 minutes of red/blue point convergence work - spend more time on the general geometry-related convergence adjustments sooner.

REMEMBER: Avoid point convergence until the very last step, don't be lazy - you will have less convergence drift problems in the long run if you use the general geometry adjustments first to the best of your ability before hitting the point convergence.

REMEMBER: Save your settings once every few moments while converging. Don't rely on the auto-store feature to back up your settings. Also, when you're finally done, make a copy of your memory slot as a backup. And also, if this is your first real convergence attempt, you should save a copy of your settings into the master memory slot (the "default") so it's quicker to converge the next video mode, by using the default settings that will sometimes do 98% accuracy, saving you a lot of work - even a whole weekend of work!

REMEMBER: You have to repeat all these steps for each different video mode or different computer resolution/refresh rate. It's a big hassle, so keep your resolution selection to a limited subset. You don't need to repeat the mechanical focus/convergence, but sometimes you may need to repeat the focus/astig steps. Often, if you save your settings to the master/default memory slot, you usually don't have to re-focus/re-astig but you should doublecheck everytime you create a new memory slot for a new video mode that's going to be used frequently.

I may have missed a few steps, but I think all of the above basically sums up what you need to do. You have my permission to integrate the above into whatever FAQ comes up - just make sure you give me a chance to proofread it, and give me credit.

And if there's any errors, please do not hesistate to let me know! Also, be noted that this HOWTO does NOT cover greyscale calibration. Just DIY project convergence.