CurtPalme.com Home Theater Forum

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

Why does my NEC 9 pg have triangular dots at the edges of the screen that for some reason cant really be corrected, and the edge focus setting is around 70-80 on both horizontal and vertical, center focus is spot on at 0, and green is worse than red and blue?

Center is fine on all 3, edges just seen to require alot of correction, and no matter what i did when doing the astig magnets, i couldnt get those edge dots to be round!!

**AnalogRocks** · Posted: Fri Nov 05, 2010 5:09 am Post subject:

Maybe the edges of your picture are hitting warp speed Laughing

benny · Posted: Fri Nov 05, 2010 7:25 am Post subject:

Correcting triangular dot shape is the job of the static 6-pole CPC magnet assembly and in better makes/models, a 6 pole dynamic electronic system, such as found on the Barco 909 . Alas, The 9 PG doesn't have them.

The reason the dots appear more triangular in shape on the edges, is largely because the beam hits the phosphur face in that position at a greater angle then right in the centre, where it is at 90 degrees. The beam is also less controlled at the edges and hense splays out more, thus making it more noticeable.

There may also be some optics limitations you are noticing.

Russ

**Curt Palme** · Posted: Fri Nov 05, 2010 2:02 pm Post subject:

It also appears to be somewhat set dependent. I've seen some XGs with perfect round dots everywhere, and some with triangular dots at some edge(s) of the set that you simply can't get rid of. I swapped all sorts of boards, focus, astig, wave, system, etc seeing if I could improve it, and I couldn't.

If I get another one in, I'll do some more playing, esp with swapping astig magnets to see if that helps.

jarseneau · Joined: 06 Nov 2007 Posts: 323 Location: WI

My advice that follows is based on my personal experience and if anybody can improve upon it please feel free...

My advice for edge astig is that using a test pattern of +'s or a fine crosshatch will make it easier to dial in astig than by using round dots. The advantage of the +'s is that you can see the effect of the adjustment in a way that gives you a better indication that you are going in the right direction. While the round dot may change shape, it will never be a round shape and so you can never tell if it got better or worse in terms of improving the astig.

With the +'s, you will see either the horizontal line get fatter or vertical line get fatter, so the key there is to balance them to equal fatness. Once you've balanced, you can use focus to shrink the lines. If the +'s smear diagonally, then you want to minimize the smear by rotating the magnets in unison. The final test is to turn on one of the other colors and then ramp focus up/down to see if the adjusted color moves vs. the reference color. When Astig is correct, it should not move by changing focus.

**Curt Palme** · Posted: Fri Nov 05, 2010 5:40 pm Post subject:

Bang on Jerry, I've done that as well, in fact I often use the fine crosshatch on the Marquees to adjust astig, both on the neck and in the menus.

andreas · Joined: 31 Mar 2010 Posts: 92

ive noticed this to! im adjusting my marquee this way and improved astig alot! But just fine tune this way.

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

Thanks everyone, sorry for delayed reply, i dont have the internet at home.

It sort of struck me as abit odd that the center is pretty much bang on perfect, and the outer edges, more so the corners and in the case of the green, more so on the left, the blue and red are pretty equal and both abit better than green.

When i was doing this i tried moving the focus yokes back and forward on the tube neck which seems to do almost nothing, ofcourse it means i have to turn the focus pot, but it does nothing really for the corners and their triangles, so i put them back where they were when i got the set.

The edge focus setting though is way up, at about 70-90 is where it is best on the plus side, the center focus for each tube is zero and at its best there. I wouldnt think that is how it should be.

What made me wonder so much is my Sony VPH 1001-QM has round dots across the whole screen on all 3 tubes, and was very easy to do too, it seemed strange an ES set could do it easy and an EM cant!! The focus is better on the NEC, but not by much, the Sony has near new 07MS tubes, but the set is very experienced.