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I bought a second hand Sony VPH-D50QM from my work place at an excellent price. It had less than a 1000 hours on the tubes and was generally in excellent condition.


There is one problem however, I can not seem to get the blue tube focused sharply.


I’m new to CRT projectors, but I’m 99% confident that this is not a optical focus problem, but rather seems to be a problem on the tube face (focusing electron beam possibly?). This is quite puzzling to me as the set was obviously set up by an expert when first installed in the work place so I can’t understand why the blue tube wouldn’t have been set up properly when the other two were, or why the blue tube would develop a problem when the other two seem perfect.


There are some magnet levers inside at the back of the tube, I’ve had a quick play with them and while I can make the focus much worse, I can’t seem to make it better.


Any suggestions would be greatly appreciated.


I still rate the picture quality as excellent but it’s really bugging me because I know it’s not as good as it could be.
 

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The blue tube never gets focused sharply. One reason is that a highly focused blue tube won't put out nearly as much light as a slightly blurred blue tube. (This is just the nature of the blue tube.) In order to get good greyscale tracking, its normal for blue to be a little defocused to get the higher light output.


Second, your eyes just aren't as good at resolving blue as they can resolve red and green. So its also pretty normal to be difficult to locate the "perfect" focus point.


Did you get your blue optical focus correct using the phosphor grain technique? This is really quite simple to do, and works exceedingly well. If your optical focus is correct, then move on to electronic focus, and then astig. The blue will be a little bit defocused compared to the red and green, but you should still focus it as much as you can. Some recommend then blurring it a tad, but without a color meter and the skill to set it properly, there isn't much point (IMHO).


Oh, those magnet levers you played with? Guess what, they are the astig rings. Read through holy focus. When Guy is talking about adjusting the 2 and 4 pole magnets, those are the rings he is discussing. What you want to do is setup a dot pattern and adjust the rings as the Holy Focus document describes.


Gee, I'm starting to think that Holy Focus is becoming the Holy Guide to CRT setup. :) Now if only we had Holy Square to Screen to help my current woes.... :D
 
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