WG & a great green smear in the picture...

[SoundDoc]

Hoping someone can help me here, (MonitorGuru where RU...)

I'm still working on my cab, new baby has seriously slowed it down though...

The cab I'm restoring came with a 25" WG k7000 monitor, one problem, broken neck, so I went dumpster diving, and found a replacement 25" tube. Swapped tube, resoldered the chassis, cap'd it, and low and behold! I had a picture! although dim. As I was lifting it into the cab, I slipped, and yes, I broke the neck on this tube, and cracked a couple of the pots off the neckboard.

After much cursing, I located another tube, performed a second swap, rebuilt the neckboard. (the only thing that stands out is that it was the green drive adjustment that broke off, but it was replaced with same value pot) I have this tube up and running, but even after checking everything 5 times over, I have a smear on anything green. What I mean is, any green text, or graphic, has a smudge to the right  that trails off, it ranges from .5" to 2" long sometimes.

I've checked everything I can think of, all new transistors on the neckboard, I don't see anything odd on the scope or video test gear on the signals, but this green smear won't go away! Its like a spray or wash, or fog that trails to the right is the best way I can think to explain it. I believe its actually fading in to the left as well, as when a full raster is thrown up, red and blue are symetrical and sharp rectangles, while green kinda fades in on the left edge, and fades off on the right edge.....

I thought it may be the green transistor not turning off fast enough, but swapping it made no affect, so I'm not sure where to look.

Anyone thats worked on monitors much ever seen this?

SoundDoc

[Ken Layton]

Could be your green color adjustment pots on the neckboard are set too high. Could also be the contrast control set oo high.

[SoundDoc]

thanks for the quick reply Ken, I went through the monitor again, and even with the green drive and cutoff at the minimum, and the contrast very low, its still there. (I brought up a black screen with a white rectangle, and even with the raster just visable, the problem exists.) I'm going to try and get a video analyser hooked up to it this weekend to look at the signals right at the neckboard, and see if I can see anything.

Before I broke my origional replacement tube, I had it setup on the bench, and there was no green smear at that time, so I think I'm going to pull the chassis & neck boards again and go through them to make sure theres no damage I missed when the neck broke off.
Could it be a bad cap on the neckboard?

Could there be something wrong with the tube? I'm a electronics engineer, and spend most my time working on radio and electronics design, and I have to say I'm fairly weak when it comes to the "intricacies" of monitor work. I've repaired many monitors, but never tried a tube swap before, and don't know if there is anything I was just completely missing.

Any other ideas?

sd

[Ken Layton]

It could be a tube problem. If you can get a picture tube rujevenator hooked up to it at least you can check the condition of the tube to rule it out. Double check the neckboard again for anything you may have missed. There's only one electrolytic cap on the k7000 neckboard (C204). I've had problems with the color trimpots actually developing hairline cracks internally so unsolder them and test with an analog ohm meter.

[SoundDoc]

I'm bringing home some additional test gear tonight to test the monitor and see whats going on. I hope its not the tube, I don't have easy access to a tube rejuvenator, but I believe if its the tube I could get the repair shop I bought it from to swap me another.....(charged me $10, not too bad)

I'll post when I have more info.

SD