CurtPalme.com Home Theater Forum

amigaman

Hello all.

I recently started a thread saying that my menus and test patterns on the XG75 were jittery, but now I've found that there is an overall instability issue with the phase adjustment between the input video and the test pattern/point convergence systems.

The problem exhibits itself as overall unstable convergence. I can have the projector on for 30-60 minutes at least, align it, then when I turn it on and let it warm up the next day, it's a little off again. It also causes the menus and test patterns to jitter and shift horizontally.

It seems like to me that the sync circuits for the digital side are having trouble locking to the horizontal sync of the video. The video overall looks good, with no jitter. It's just the menus, patterns, and point convergence (and possibly some of the normal digital convergence as well) that are jittering and shifting.

I generally find that problems like this are caused by bad capacitors, cold solder joints, and sometimes bad connections, but lacking a real service manual, where should I look first? Are there any boards in particular that often show issues, or any components that commonly fail that should be replaced?

If anyone has a link to the NEC XG75 service manual, that would be amazing too.

Thanks!

**Curt Palme** · Posted: Tue Mar 15, 2011 12:22 am Post subject:

Try cleaning the H yoke connectors on the H deflection board with Caig contact cleaner. I've had several XGs in the past cause H shaking on all or one color due to bad connections there. Drove me nuts for about 2 hours as I swapped system, wave, convergence, etc boards, all to no avail.

amigaman · Posted: Tue Mar 15, 2011 3:12 am Post subject:

The raster (and image from the inputs) don't jitter. It's just the test patterns and on-screen display, and in turn the phase alignment screen (making accurate phase difficult), and what seems like the point convergence horizontal phase along with it, if that makes sense. All colors shift equally and simultaneously, not just one tube, which would lead me to believe the issue is before the individual tube convergence and deflection stages.

Good suggestion about the H yoke connectors though. I'll do that to prevent future issues.

Could someone maybe provide me with an idea of what each board does (like the convergence boards between the CRTs), so I can pick a place to start checking for bad connections and bulging caps? The projector is on the ceiling, so a bit more of an ordered approach would be better than just pulling all boards and connections for inspection.

A previous post said that menu jitter was "normal" for NEC's, but this is pretty bad. If I catch it in action again, I'll try posting a video of the jitter.

**Curt Palme** · Posted: Tue Mar 15, 2011 3:15 am Post subject:

It could be the system board if you're sure the raster is stable. Easiest way around that is simply get an AVIA or other test disc, and use the test patterns on that.

amigaman · Posted: Tue Mar 15, 2011 7:13 pm Post subject:

I'll look for obvious problems, and see what I find. I only did a super fast alignment to make sure the projector works properly. I haven't gone in to adjust the centering and astigmatism magnets, which clearly needs to be done, considering how far I have to push the menu controls to center up the raster on the tubes.

Another question though, while I'm on the subject of instability:

I'm projecting a 16:9 image, in multiple HD formats, which works, but as I turn up the horizontal amplitude to maximize the width, the horizontal linearity shifts off when I hit around 75% amplitude or higher, and goes away when I shift it back down to 60% or so. With it wide, I can fix the linearity with the menu controls, but I have to nearly max out the horizontal linearity control to do it. I've done the horizontal width calibration outlined on this site with a 480i signal, so I shouldn't be overloading the H drive circuits.

Is that normal, or is something wrong? The linearity might be shifting a bit with time, but I haven't checked it in a little while.

amigaman · Posted: Wed Mar 16, 2011 1:46 am Post subject:

I cleaned the H deflection board connectors, and inspected and re-soldered any connection that looked like it might have been bad on that board, and there was no change. I also checked every board in the card cage at the back for bulging/leaky capacitors, and other visual signs of a problem, and found nothing. Also reseated the socketed IC's, with no change.

I shot a couple quick videos with my phone of the green tube, showing the instability issue. Normally I wouldn't be bothered by it, but it affects the point convergence phase, as well as the OSD and test patterns.

http://www.youtube.com/watch?v=4Cy7M0GiGeA
and
http://www.youtube.com/watch?v=M-CtSMipslk

Ideas? There is a single brown wire in the ribbon cable connected to the MD socket on the H deflection board which appears kinked/twisted right next to the red tube neck board, which might have a break in it, so I'll splice that and see. Anything else it might be?

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

From the videos it looks like you have a valid incoming signal. Have you tried other resolutions to see if that makes a difference? Something like 1024x768@60hz should be safe. If that works, perhaps there are cable or PC video card issues.

amigaman · Posted: Thu Mar 17, 2011 8:21 am Post subject:

All resolutions behave the same way. Tried 480i, 480p, 720p, 1080i, and 1080p.

I think I've found the problem though. With the hinged assembly that holds the H deflection and HV boards open (away from the CRTs), I get clean images, with no horizontal linearity distortion, but the distortion comes back as soon as the assembly is closed. I thought that some sort of interference between the CRTs, either the deflection yokes or the HV leads, might be getting into the H deflection board. As a quick fix, I covered the plastic insulator cover on the back of the H deflection board with aluminum tape, and grounded the whole layer. This completely fixed the issue, and even though the menus/patterns still jitter (slightly), there is no more drift or distortion in the convergence.

Odd issue and fix, but it is working amazingly well now. I did the aluminum tape trick on a plastic covered board in a Sony broadcast videotape recorder a while back which was having interference issues with static electricity, and it worked on that too, so maybe there's just a little more HV leakage than normal from the CRT anode leads.

Everything is well intact with no arcing or anything, but if there's anything I should still be concerned about, I'd like to know. It has been running problem free for 6 hours or so today with no drift or linearity issues, so I'm happy. We'll see if it stays that way when I power it up tomorrow.

amigaman · Posted: Thu Mar 17, 2011 4:20 pm Post subject:

I realize in a previous post I said I needed to adjust the centering magnets, but that was before I was aware of the raster centering adjustments in the adjust ref. menu. I had assumed it would be similar to my 9PG Plus deflection wise, but I'm learning the differences.

As of today, the alignment is still holding, with no drift issues, so it looks like that simple shield fixed it all.