CurtPalme.com Home Theater Forum

[JustGreg]

Finally getting back to working in the HT and have a couple keystone related questions.

As with all displays, when adjusting keystone the image can be 'rotated' from a screen center 'axle'. Running it to zero pulls the top toward the pj, and conversely adjusting to 100 brings the bottom 'closer' to the pj. Both extremes produce an on screen trapezoid as is normal.

I'm still trying to get my head around why I need the pj lowered down toward a zero angle (pitch?) and the screen angled out at the bottom 10 degrees to achieve good keystone; with reasonable numbers. All the boards have been swapped but the same deal no matter what I do. With the pj's built in 10 degrees and the screen at 10, I have 20 degrees invested and no joy.

As I evenly lower the projector more (tube centers in line with screen horizontal center), and keeping the base bubble level, I should be seeing minimal (EDIT: sub the word lower here) keystone requirement, which I am, but not to the extent I thought it should produce. Obviously I don't have the pj centerline level with the screen center because I have a rear riser, but the top of the pj (inverted, so I'm talking about the feet base) is ~4 inches below the top of the screen already. And yet I still have to run keystone up to around 80/90 to get a good on screen grid. At the tubes it's an ugly story. I'm seeing a definate trapezoid at the faces...which aint cool at all. I never had this 'problem' with the old tubes. I had nice even wear.

1) Can the keystone circuit be modified to deliver more keystone range, eg, increase the range like as is done with the H size circuit? (R609, 709, 809 IIRC?). I want more range to exaggerate the rotation in both directions. I"m not overly concerned with heat at the heatsink now as I just finished my liquid cooled heatsink project. Works like a charm. I'll post pix when I get my camera back from relatives.

2) Even tho I can compensate electronically, I really hate to do this to a new set of tubes. Am I doing something wrong?...or just expecting too much of it.

TIA folks.

[stefuel]

Post pictures of the projector shooting onto the screen from the side and post a picture of the green tube face with a test pattern showing.

If you can, also provide the following measurements. 1, floor to the base of the projector. 2, floor to the top of the useable screen surface. 3, distance from the center of the green lens to the screen.

Every time I read one of these complaint threads it's the projector mounted incorrectly. If you followed the manufacturers installation instructions, you should have no problem dialing it in without tilting the screen.

[JustGreg]

[Tim in Phoenix]

Guys!

There is another possibility. Keystone is corrected by modulating the H size at the vertical refresh rate. You could have an HDM issue, or an issue with the waveform driving keystone correction.

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