CurtPalme.com Home Theater Forum

[Apfelmousse]

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Hi all,

This is a question beyond operation or installation / adjustment.

Planning to setup my G90, I have passed a whole day reading setup guides and such about raster and image positioning. In a nutshell, I have a raster that I can setup and that defines the electron beam travel across the tube face. And then I have an image from the video inputs that I can size and position somewhere on this raster. Without modifying the raster!

As an electrical engineer, I'm wondering how this works technically. How do they manage to define the starting point of the image on the raster? With internal timers? But in that case, when the next image comes up on the video input (i.e. after 1/50th of a second), it wont't wait until the electron beam of the raster will have reached the required starting point. What happens during the time the electron beam is travelling outside the image window?

And how do they control image size on the raster? I imagine the electron spot starting its travel on the left, then after some delay the image is modulated on it. Given the constant speed of the beam, how do they manage to stretch the image without modifying the speed of the electron beam (i.e. without modifying the raster)?

Same for vertical. I imagine each line of the raster belongs to a line of the image. So how is vertical image size controlled without modifying the raster, i.e. the number of lines of the raster?

cheers
Martin

[Apfelmousse]

I just finished another setup of geometry (called registration by Sony).

I followed helpful advice from Craig and others. I put all and everything to 128 before. I wonder what the reset-menu "set to 128" is good for, since it does not put anything to 128...

Then I did the raster centering on the tube-face, followed by centering on the screen using the outer edges instead of the centre. I carefully adjusted the different geometry steps, and ended up with a convergence ("zone") adjustment that only required very small corrections. NICE!

Since I also did a factory reset at the beginning, my colour balancing problem is no longer a BIG problem. I still want to try doing it properly with some measurement device.

Conerning RASTER and IMAGE: they do not seem to be independent at all. Horizontal and vertical frequency and timing of the RASTER are related to the IMAGE. I can only shift the image within limits, and it warps around if done too much. This is actually exactly the same as on an old TV-screen where I could tweak horizontal sync (phase control) in a way the image shifted from right to left. The only difference is that you never noticed the raster on the TV-screen as it was always outside the screen area and you did not need to care about.

Now I understand why it is important to do the geometry with a test pattern from the actual source. Internal patterns are OK to do mechanical and focus alignment which are independent from the raster. As soon as it comes to raster alignment it is better done with the exact frequency and timing of the source signal.

Is it so, or do I miss something?

cheers
Martin

[gjaky]

You pretty much figured it out already.
But here is a little more information if you are still interested.
In their truest nature CRT projectors all based on accepting RGBHV signals, ie. separate color luma signals and separate sync signals. The sync signals contain a train of pulses, the repetition frequency determines the scanrate and refresh rate obviously. Now, for stability reasons the sync pulse needs to have a certain pulse width so the receiver electronics can reliably lock to it. As the electron beam needs to travel back to the start point after finishing one line (or one frame for that matter) and this can't happen in zero time this needs to be considered during setting up the display timings, this is most often referred as horizontal and vertical retrace time. We are getting closer... so we have a defined repetition rate of the sync signal, but because of the retrace time and needed "sync width" (and some other factors too) we can't use all of that time for drawing the picture within, this is called blanking time, which is depending on projector model and sometimes even on scanning frequency range. Everything that falls out of the blanking time of the projector becomes what we call the raster.
When defining display timings there are four parameters for each plane those are of concern: the active picture area, front porch, back porch and sync width, all these can be given in pixels for sake of simplicity. Ideally sync width is used to simulate the blanking time front and back porches are used to position the active image within the "low state" of sync signal.
CRT projectors, however, never use directly the sync signals, rather PLL circuits are used to lock on the sync signals, because the sync signals and video signals go on different routes in terms of electronics, their timings will surely differ while the picture gets drawed on the tube face. Therefore the PLL phase can be altered to be able to set the active image part related to the sync signals.
Practically it is desired to taylor the display timings to the given projector's abilities so bandwidth (and possibly scanning) requirements could be optimalized.

[Apfelmousse]

[gjaky]

[AFryia]

[Apfelmousse]

Hi all,

here is a picture I took after having set everything to 128 (except focus controls), before aligning the tubes.

I wonder if it is normal that the blue tube is a so much lower than red and green. Is there a mechanical part or a trimpot somewhere where I can manipulate vertical position / size before applying software controls? Like the 3 adjustments for horizontal witdh.

The second picture (actually the first in the post - how can I swap these?) has been taken after tube lineup and first setup of size and position. No linearity / pincushion / keystone / zone.

I watched the CRT setup-video. Its for a G70, so very familiar to mee by now. Yet a slightly different approach, but well explained and rather intuitive. The only thing I didn't understand is that it seemed he never actually adjusted the projector height - the image was vertically out of center (too high) all the time he did the adjustments. I must have missed the moment where he either adjusted the vertical position values, or raised the back of the projector.

cheers
Martin

[AFryia]

[Apfelmousse]

[km987654]

[Apfelmousse]