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Discussion Starter · #1 ·
My Barco Graphics 808 is exhibiting some strange behavior. Fairly often now I'll see that the picture has become distorted, and each time it is due to distortion from the blue gun. If I put up a grid pattern and display only blue, there are bumps in some of the lines, some of the lines will be faint, and there are very faint lines from a duplicate of the grid, but shifted to one side.


I replaced the blue gun with a VDC rebuild back in September, so I immediately thought, "Uh-oh… the VDC tube has crapped out." I commenced with opening the shroud to inspect the internals, and as soon as I touched that big access screw, a small electrostatic spark from me to the screw occurred, and the blue gun snapped back into shape! Distortion gone!


This distortion crops up every time I use it now, and my "fix" is to shuffle around on the carpet, then simply walk over to the projector and touch that big screw (which is obviously grounded to the chassis). The resulting electrostatic spark rights the blue CRT distortion every time.


This is obviously not correct behavior. What's going on here and what's the permanent fix?


Thanks,


Steve
 

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Steve, I don't know how to fix it permanently. Sounds like maybe a missing ground strap or ground wire to the blue CRT? But anyway I will have to remember the carpet trick. I think you may be on to something!
 

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mr_ro_co,

As I was reading your post I came to the same conclusion as matrix, I think he hit it on the head. There is a conductive coating on the back of the crt that makes contact with some type of grounding strap or finger, make sure this is making a good contact, that'll do it, I've seen this before.

KevD
 

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Discussion Starter · #5 ·
Dennis, KevD, I will look into this. I installed the gun myself... I remember the lip of the bell having a spring loaded metal wire attached to it that was then somehow connnected to the tub... The bracket it sits in should be grounded to the chassis. I'll investigate the integrity of that connection.


Thanks,


Steve
 

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Can you post of Pic of it ??

CRT's use the CRT itself as a HV cap there is a conductive plating on the inside of the CRT and the out side

this make a capacitor the outside need to be tied to the ground. Some times you will see a braided wire tied to a spring stretched over the back of the tube to do this.


This might be a neck problem can you swap it with a different color and see what happens.
 

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Discussion Starter · #7 ·
sly,


I will post a pic of it the next time it happens. I'll see if I can get my cheapie digital camera to capture a line pattern on my screen, otherwise I'll have to pull the blue lens and shoot the crt face.


Yes, the VDC tube rebuild does have a spring loaded wire attached to the bell lip in some fashion.


By neck problem, are you proposing I connect the blue's socket to the green tube to see if the same thing happens?


Thanks...


Steve
 

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"are you proposing I connect the blue's socket to the green tube to see if the same thing happens?"


yes just swap them if now happens on green then it is a problem with the PJ or the neck board if it still is the blue

then it has something to do with the CRT.
 
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