CurtPalme.com Home Theater Forum

nuttall_chris · Posted: Tue Oct 30, 2007 11:29 pm Post subject: Green P19LUG Issue on Marquee

I seem to be having a problem with the green tube on my Marquee 9500Ultra. FYI, this is a brand new P19LUG. I've put less than 20 hours on it from new (mainly trying to sort out this problem) and the problem was there from the beginning.

Whenever I turn on the projector and the high voltage comes up, the background, where the raster should be lights up, making it impossible to get "real" black from this tube. This is not coming from the video inputs, I have tried disconnecting everything including the neckboard and the G2 lead but the haze is still there. The only way to make it go away is to disconnect the HV lead from the splitter. I have also tried adjusting the G2 all the way to 0, as well as setting the brightness and contrast to 0 but the haze remains.

It looks like a very out of focus, fuzzy rectangle, slightly larger than the raster.

This tube also seems to have a very slow decay rate. By that I mean that if an image is on the tube face and then the image goes black, the tube appears to retain that image much longer than I would expect. If you look into the tube face you can still see the image for up to a minute after it should have disappeared and has disappeared from both the red and blue tubes.

I also noticed that when I power down the projector I see something that looks like a rose bud appear in the middle of the tube and then fade away.

These pictures were taken with the neck board and the G2 lead completely disconnected. The only thing still connected to the tube is the main HV lead. The magnetics on the tube (focus coil, convergence coil and the deflection yoke) are active and functioning.

The same result can be seen with the neck board and G2 connected.

I emailed Terry and he suggested that it may be contamination inside the tube shorting out one of the guns. He suggested that I ramp the G2 of this tube up to 100 for a few seconds to see if it will burn off the dirt.

I have tried the procedure described by Terry. After about 5 seconds with the G2 at 100 the HV supply appears to restart (all tubes go black then refocus as the HV comes back up). I tried this a few times with no luck and no change in behaviour.

Has anyone ever seen this before?

Chris.

overclkr · Joined: 08 Mar 2006 Posts: 4227

Sonynut · Joined: 08 Aug 2006 Posts: 367 Location: Bradford,PA

OT-- Hey Cliff, what movie is your avatar from?.. looks familiar..

nuttall_chris · Posted: Wed Oct 31, 2007 1:37 am Post subject: Re: Green P19LUG Issue on Marquee

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Looks like a high G2 short. Can you find a Sencore CR-7000 or any other good CRT tester to test the CRT ?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Afterglow on a green tube can last a LONG time. I've watched a movie, shut down the PJ, turned out all the lights, gone to bed, and gotten
up two hours later, passed the PJ, and seen residual glow from the green tube.

You MIGHT try swapping neck cards with the next tube over. See if the green tube continues to have this lack of black issue.

CJ

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Are we talking CRT phosphor persistence or a constant low level glow when turned on ? Could be a bad neckboard. How many hours on the tube ? Still sounds like the CRT ... Confused

nuttall_chris · Posted: Wed Oct 31, 2007 12:00 pm Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Well I'll take a little guess. Since you only have the hv connect the cathode shouldn't be emitting any electrons. The electrons are needed to strike the phosper to make them glow. So whats making the phosper glow. Well the anode when charged is like a magnet so it must be attracting particles in the tube. Since the tube is new, there maybe a negatively charged contaminent or maybe not a complete vacuum. Any air left in there could cause who knows what kind of problems. Lastly maybe lets over electrons, but I dought it since they done last long. Something is making the phosper glow and only when the anode is charged.

**Curt Palme** · Posted: Wed Oct 31, 2007 2:40 pm Post subject:

I'm with Terry, this sounds like cathode contamination. Is this an NOS tube? This can happen if the tubes sit around unused for a long period of time. VDC can fix it for you.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Also found this little article which explains things a little:

When a television set is switched from the "on" mode to "standby" mode or OFF, a ghost image may appear on some of the used cathode ray tubes (in the following abbreviated as CRT). This effect is called stray emission or after-glow and is normally caused by particles, in other word contamination, trapped at Grid 1 or at Grid 2 of the electron mount, i.e., electron guns, accelerated by the anode voltage (referenced as EHT for extremely high voltage) and hitting on the phosphor of the CRT. Due to the current CRT manufacturing process, it is not possible to eliminate these particles completely. CRT manufacturers normally guarantee that stray emission is suppressed if the EHT voltage is discharged immediately to a specified level (e.g., 18 kV) when the TV set is switched from on to standby.

I'm betting on contamination!!!!!

Ron

nuttall_chris · Posted: Wed Oct 31, 2007 2:49 pm Post subject:

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Personally I think Terry and Curt both need to invest in a good CRT tester such as a Sencore CR-7000 before selling and stating good emmisions from any new or used CRT... Wink

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

With the neck card off there is not any heater voltage to produce electrons, and even if the gun was able to produce some electron flow from stray current of the anode it would probably be in a straight line and not the full raster since you said the deflection coils are also disconnected unless the flow is so slow it has time to scatter which would also indicate the dim raster. I'm still thinking possible stray charged particles.

nuttall_chris · Posted: Wed Oct 31, 2007 4:51 pm Post subject:

nuttall_chris · Posted: Wed Oct 31, 2007 4:56 pm Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Oh. In your one post you said the only thing that was connected was the high voltage. Did you try it with the coils disconnected?

Tom.W · Joined: 09 Mar 2006 Posts: 6635

And how do they fix it ?

nuttall_chris · Posted: Wed Oct 31, 2007 5:02 pm Post subject:

Sorry, I guess what I meant was that the only thing electrically connected directly to the tube was the HV.

The projector wont run if I disconnect the deflection coils, you get a horizontal fail alarm and the HV won't come up. The only way to test this would be to remove the tube from the projector and remove all the magnetics and coils, then only connect the HV lead.

Chris.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Hmmmm. Will it run with the vert deflection board pulled to see if you get a flat line?

I'm just thinking if it is electron flow from the gun then this might verify it.