CurtPalme.com Home Theater Forum

Mark_A_W · Posted: Tue Nov 17, 2009 2:17 am Post subject:

Looks better.

Do you have some ringing (aka jail bars) on the LH side?

Kiev Savoie · Joined: 25 Oct 2007 Posts: 432

So that's what you call it. Yes, I've noticed that too, but I had more pressing concerns with the wear. What do you know about it?

Mr. Green · Posted: Tue Nov 24, 2009 11:35 pm Post subject:

Mark_A_W · Posted: Tue Nov 24, 2009 11:37 pm Post subject:

Nup. It's not a "fault" usually.

It's the beam settling after retrace. You need more back porch pixels to push it out of the way.

Mr. Green · Posted: Tue Nov 24, 2009 11:47 pm Post subject:

I've never understood what people mean by "porch". It that done on the projector? I've only got a PS3 hooked up (no PC) so no clue if it has any controls that would make a difference.

I'm just curious. Curt's working with me on another problem, but I figured I'd ask since it was mentioned. If I can get rid of it at the same time I flip boards around I will.

Mr. Green · Posted: Wed Nov 25, 2009 12:13 am Post subject:

I found this post, but I still don't know what a porch is.

https://www.curtpalme.com/forum_archived/viewtopic.php@t=16679.html

Mr. Green · Posted: Wed Nov 25, 2009 12:30 am Post subject:

Alright. Looked into it more and more. Just did a search for porch under the crt projectors section and found several posts. I'm pretty sure I can manage it.

I still don't know what a porch is though.

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Hi Chris, the back porch is the beginning of the video signal or where the area before the beam begins the actual video. To help eliminate ringing you can increase the raster size to where it overlaps the tube face or goes off the edge. it will not harm the tube as long as no active video also goes off the tube for an extended period of time. So you can increase the total video pixels but keep the image or Active video pixels the same. I think on my marquee i put total pixels to 2500 or so to give time for the beam to settle before it began the image. that side of the raster was way over the edge. ran it like that for about a year before I got the LongBows.

here is an excellent tutorial on Video signals;

Building Blocks of a Video Format

Athanasios

Mr. Green · Posted: Wed Nov 25, 2009 2:04 am Post subject:

You are using powerstrip on a PC to do this, yes?

I only have the PS3 hooked up to it so have no controls other than that on the projector. I did notice my raster isn't centered since the last time we played with it and reset everything. I'm swapping out some boards soon to try to resolve another problem and will redo the entire setup. It didn't have the jail bars when I first got the set. I'm sure it's because the raster is too wide and the image is close to the tube edge on one side. It's a good thing I don't use it much right now. I'll work on it as I get time and advise.

Wow, that's uh technical. Good that they have pictures though... Wink

Now I get what porches are though, thanks!

Kiev Savoie · Joined: 25 Oct 2007 Posts: 432

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Well... I am trying to think of a good way to explain it. There are a few things that play into raster ringing. the main one is not enough room on the retrace for the electron beam to calm down, and 1080p excites it or it moves much faster than other resolutions, unless your maxing out refresh rates like 96 or 120 hz. those will cause ringing also with lower pixel counts. I had massive ringing when i tried 1064x800 at 120 for my blend.
the back porch is the the area before the start of the video or active video, this is where you need to make the largest in size to help give the beam time to calm down before painting the image. look at the image below to get an idea of what I am describing.

Now to do this you need either a PC or a VP where you can create custom timings. But as you add more pixels you increase
the pixel clock. So with 1080p you have to make sure the pixel clock of any device your trying to get the new timing signals through can handle it. there are some programs out there where you add the timings and it will show you the pixel clock value as well.

Now you can move the image on the tube as far to the right as possible to give more room for ringing if you do not have a way to add more pixels to the back porch or sync.

And making the size on the raster smaller will not give it more room as that is only reducing the raster as well.
with the VP you are actually increasing the raster size, so then your able to make it go over the tube face edge and then you would use your phase control to move it to the center of the screen. Well thats one way to do it. I am sure others will
have different methods.

Athanasios