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Discussion Starter · #1 ·
This works very well for me, but should only be attempted by someone who is already quite adept with the CPC magnets on the NEC XG.


Your results may vary and there is definite risk in attempting this advanced level of EM astigmation and focus adjustment. Consider this TECHNICIAN level only.


Basically, I attain tighter EM focusing by doing astig backwards from the normal convention. Beware, that once you start you basically have to COMPLETELY realign the and converge the machine. Don't do this unless you are willing to spend one or two days on it. You can't easily go back to your original settings so I've hesitated in discussing this method, but it's time to push things another step on the CRT side after spending a few months pushing the DLP side forward.


The problem that this corrects is that the astimation error for the beam is not necessarily best corrected by making the underfocused beam round. One normally does astig by making the underfocused spot round. I get a better result doing things in the overfocused state (bright spot with halo). The problem is that the XG is not designed to allow this easily.


Here is how.....


1. Display a signal of the highest frequency to be used (or highest resolution that needs to be optimized). The XG only has one astig memory so you need to choose the resolution for which you want to optimize. (Wish it was like a Sony with multiple astig memories)


2. Zero out all focus and astigmation controls (center, edges, corners). Then intentionally set center astig to maximum H/V and physically rotate the EM focus coils to make the H/V astig perfectly vertical for each gun. Set H/V back to zero. Retighten EM coils.


3. Set blue focus tracking OFF in options menu.

4. Set contrast to 75. You don't want to be at this contrast too long with the guns focused so have that remote handy and be able to cut off the guns ASAP.


5. Display a Coarse Dots pattern and immediately cut off all but the gun you are working on.


6. Take an insulated adjustment tool and turn the focus pot for that gun clockwise (overfocus) to make the flare on the screen about 3/4 to 1 inch in diameter. The room must be DARK and your eyes well accomodated. I use a pair of binoculars for examining the screen and also mark the center dot with a lightly affixed piece of 3M brand blue masking tape (use NO substitutes!).


You will see a central bright spot and a halo around it.


7. Adjust the shape of the halo with the 4 pole CPC magnets (2nd rearmost) to make it round for the center of the screen. I make things round first to make it easier to see how well centered the bright spot is.


8. Center the bright spot in the round halo using the 2 pole magnets (rearmost)


9. Observe the halo for any residual rays of brightness or triangularity. Use the 6 pole magnets (most forward of the CPC) to remove any triangularity in shape or rays in the halo.


10. Refine the 2 pole and 4 pole adjustments until everything is just right.


11. Repeat for the other two guns. Be sure to cut off the two guns not being currently worked upon.


12. You'll note that all three guns now have their CPC magnets optimized. Close the deflection cover. Roughly recenter rasters in the reference adjustments.


Now comes the neat part of this technique......


13. Select electronic astimation by pressing control and focus on the remote. This changes the beam focus, but you will use the MANUAL FOCUS POT to set the focal state. Adjust the focus pot for the gun being astigmated such that the on screen spot is overfocused (slightly clockwise of focused) to a spot about 1/4 inch in size on screen. Stand near the screen and perform electronic astig for center, edges and corners.


14. Repeat for each gun and you have astigmation perfected.


15. Select focus control mode (get out of astigmation mode) and the system goes back to normal focusing mode.


Set center focus to +50 for each gun. Yes, that is PLUS 50. All the other focus controls should still be at zero.


Display a focus pattern and for each gun adjust the focus pot to make the CORNERS of the screen as well focused as possible.


Turn contrast down to normal as soon as you finish setting the focus pots. Work fast as you don't want a high contrast setting and focused beam too long.


16. Focus the electron beams for center, edges, and corners as usual. If you find that the center focus needs to be much lower than -25, readjust the focus pot to focus the center. Some iteration between focus pot and center focus may be needed to keep things within range.


17. Recenter the rasters.


18. Redo optical focus for each gun now that the beam focus has been sharpened. Look for the Yikes Focus thread for stuff about optical focus.


19. Reenable blue focus tracking mode.


20. Perform your usual geometry and convergence setup


21. Redo color temp calibration.


At the end of it all, you should be rewarded with a tighter than normal beam focus.


This works exceedingly well for me and I'm sharing it so others can try it. The process is MUCH more tedious than the conventional method. It's actually against convention to do it this way. Because this requires good comfort with working inside the machine and around high voltages, this is NOT a suitable method for most NEC owners. I'm putting this out there strictly for those already skilled and wanting to try something squeeze out that last little bit of performance.
 

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"...The process is MUCH more tedious than the conventional method. It's actually against convention to do it this way..."


Hey, but this is when you get really good at it. KUDOS!
 

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Thank You Guy, again you push the performance limits of the XG forward.

I will do this in the next month or so, I'm to busy going ga-ga over the 1440X960 resolution right now...and having several other tweaks going on right now, I'm get familiar with what each of them has done.
 

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Discussion Starter · #4 ·
Let us know how you fare with the alternative method.


BTW, in case it isn't obvious you can also use the focus pot to do a slight underfocus during astig if you still prefer to do it with underfocus instead of overfocus. The pot will let you do astig at any arbitrary level of EM focus. This means you can defocus less than the built in defocus produced by the projector to more directly see the effect on the focused state.


Don't go willy nilly and wildly spin the focus pots. You could wear them out physically.
 
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