CurtPalme.com Home Theater Forum

amigaman

I know getting an XG to do 1080p can be a challenge, but I haven't had a real issue with it until using a PS3.

The image wraps around both sides of the raster (at 1080p only), which is't a massive problem, since not much is lost, and blanking masks the visible wrap. The big problem for me though, is the clamping problem causing dark horizontal banding whenever bright objects are near the left side of the image, which blanking and image shift does not fix.

My question is, that if I don't want to spend a whole lot on a scaler to increase the porch sizes at 1080p, is there a way to adjust the clamp circuit in the XG to reference a different part of the porch (where the image isn't spilling)? There's clearly something off, as it appears as if 480p material from some sources is causing the projector to clamp to the sync level, pushing the brightness up way too high. Is there some sort of clamp timing trim pot inside the projector that would solve the issue? This is basically a DC restoration circuit, right?

Thanks,
–Tom

amigaman · Posted: Sun Apr 03, 2011 11:55 pm Post subject:

So I found one potential solution to the problem.

Looking at the way the image behaves, I determined that if the input video signal (RGB) is delayed from the sync (HV), the blanking would be shifted into the area which the XG uses for black clamping.

To verify this, I used an Allen Avionics variable video delay line on the green channel (red and blue disconnected), and I found that a minimum delay of 240ns was needed to solve the problem. Checking the other two channels, I got the same results.

This would mean though, that if I wanted to delay the RGB from the HV, I would need 157.2 feet of extra cable on each of the three channels. This of course would work, but I don't want to wast that much coax.

So my new question is, are there any fixed higher bandwidth delay lines that you would recommend, or any alternate external methods for delaying the signal, or is there an internal horizontal sync phase control in the projector (which would be ideal)?

With my experience in broadcast video, misadjusted horizontal phase in a genlock circuit can produce this exact problem, and since the XG looks like it processes sync and video separately, I'm sure there's a similar control inside there.

Any ideas?

amigaman · Posted: Mon Apr 04, 2011 4:35 am Post subject:

Is this something the HDfury3 would have fixed?

**AnalogRocks** · Posted: Mon Apr 04, 2011 6:15 am Post subject:

You need a scaler.

amigaman · Posted: Mon Apr 04, 2011 2:21 pm Post subject:

That's precisely what I'm trying to avoid. While I know it would be ideal, they're all just far too expensive, and I'm only trying to fix a simple problem.

Since the image fold-over has a relatively minor affect on the image (after blanking it out, and it's all within standard overscan area), I don't mind that it's there.

And since my horizontal shift control is at 55% to the right, the image is clearly off-center on the input end.

So would correcting the horizontal input shift with something like a Box1020, running RGBHV to RGBHV, downstream from the HDfury2 fix the centering and clamping issues?

amigaman · Posted: Mon Apr 04, 2011 5:52 pm Post subject:

So it looks like I can return the HDfury2, and upgrade to the HDfury3 which, with its manual RGB centering controls, should allow me to shift the image out of the horizontal blanking interval.

Since the price difference is so small compared to any other option for image centering, and considering the other benefits of the HDfury3, I think I'll go that route, unless anyone thinks it wouldn't work.

Also, out of curiosity, would an NEC 9PG Plus have the same issue? I have one of those sitting here as well.