CurtPalme.com Home Theater Forum

[CRT_Ben]

Hey guys,

I've been slowly and steadily working on my theater/music/bar room, and finally I got my 9500LC mounted on the ceiling. I'm noticing a problem with the green tube now, not sure when it first appeared though - I can't see it on "screen", but as I'm still in the very first steps of mechanical setup, my screen is a white sheet tacked on the wall until I determine final image width. Needless to say, I'm not looking for subtle image defects just yet.

Here's a picture of what's going on, as well as a video of me turning the projector on, then off. By the way, the contrast was about 10 when I took these, so that's why the "No Sync" message is so dim.

https://plus.google.com/photos/104113924914052366742/albums/5773578434294460561?authkey=CMD__9C45-Hwcg

http://youtu.be/5HRLefZcf0A

I know it looks like the raster, but I don't think it is. Here's my reasoning:

-When powering on, it gets lit at least 5-6 seconds before any other tube's raster is lit
-When turning off the green tube with "Color"+"1" (or 3), it stays lit. On the other tubes, the raster goes dark when the tube is switched off (I raised the G2 on the other tubes so I could observe this)
-It does not respond to G2 adjustments at all. However, there is a "real" raster which does respond properly.
-It's fuzzy as hell, and there are strange retrace lines. The photo is not badly misfocused, it really looks that fuzzy and indistinct.

On to the troubleshooting. Here's what I've done, in this order. Nothing has changed at all, the problem has stayed with the green tube and the red tube remains unaffected.

-Swapped video cable with red tube (and back)
-Swapped green VNB for a spare
-Swapped H. Deflection cable with red tube (and back)
-Swapped HVPS for a spare
-Swapped LVPS for a spare
-Swapped G2 cable with red tube (haven't put this back, yet)

At this point I don't know what to do. The only connector to the VNB I haven't swapped yet is the large multipin connector, and that's not possible unless I swap tube positions - which isn't happening.

I really expected this problem to follow the video wire, or the G2 wire, or be resolved with one of the power supply swaps, but nothing. Could this possibly be the tube? How could the tube decide to light up with the G2 ramped down so far that nothing shows up from the regular video feed? Also of some concern is the strange pattern on shutdown, I'm not sure what to make of that. Then again it could be normal, I usually don't stare in the tubes when powering it off.

Lastly, it's important to say that other than what you see here, the green tube is normal. Good light output at G2=71 or so, and the tube seems sharp. If I can't figure this out, it's not the end of the world, but surely it has to hurt the contrast of the tube to some degree.

Thanks in advance,
Ben

P.S. I've had a similar problem in the past, but with an entirely different chassis, and the problem followed the G2 wire: https://www.curtpalme.com/forum_archived/viewtopic.php@t=8971.html I never did figure out the solution, it just cleared up one day.

[Tim in Phoenix]

Ummm

I am thinking cathode to heater short on the green tube, let's see what the other guys think. I have some new greens coming in next week.


.

[CRT_Ben]

[Nashou66]

f it is that tap the green tube while its on near the neck to possibly loosen any debris causing the short.

Also are you sure the G2 for the green didnt go up on its own? This could be it. Did you initialize the set before doing the new set up?
Sometimes that will fix any "strange" issues.


And lastly swap the entire neck board to see if it follows.
Athanasios

[CRT_Ben]

[Nashou66]

Then its the tube like Tim said. Try a wooden dowel or wooden handle etc.

Nashou

[CRT_Ben]

OK, so I roughly set my G2 values last night to determine how much this problem will affect my black level. At "rest" if you will, the green tube definitely shines brighter than the others, but it's not all that bad. In a nearly completely darkened room, when going from full white screen to black it took my eyes 3-4 seconds to adjust and see the light on the screen. Definitely something I can live with, though it somewhat negates one of CRT's best benefits.

Athan, I tried tapping on the tube with some wood, I even tapped on the plastic housing so I could hit it a bit harder. Nothing changed at all, the light didn't flicker or lessen (or grow brighter, thankfully). I stopped because I felt silly trying to bludgeon my green tube into submission, and it'd be just perfect if I somehow hit a weak point in the glass, or hit it harder than I meant to, and my tube exploded.

The only thing I can think of is using some kind of Sencore CRT tube saver in an attempt to vaporize what's causing the short. That's part of their main function, is it not?

[CRT_Ben]

One last thought...I could put a neutral density (ND) filter over the green tube to reduce light output by the appropriate amount. It wouldn't take much to get it back down to where it should be, and I can just back off on red/blue drive/G2 and turn up the contrast. Tube wear be damned, I hardly use the thing so it will still take me years and years to wear it out regardless.

[CRT_Ben]

OK, I can't say exactly when it happened, but this has resolved itself. I can now get the green tube totally dark by lowering the G2, the early raster lighting on turn on is gone, and the bright splash on turnoff is gone as well. I'm guessing there was a small bit of debris shorting the heater to the cathode as Tim suggested (most likely put there while jostling the projector during mounting), and now the debris has been burned out or fell away.

Thank you all for your suggestions! Unfortunately I'm about to post asking about a new problem, such is life