Blue "bleed-over" on RPTV

Blue tube is soft and has lower emission than the red and green. Run your contrast down while it's happening and I'm sure you'll see it diminish as you adjust. Not much you can do past that except replace the tube.

Is the blue tube projecting a sharp picture? Or are you seeing bleedover caused by dirty cooling fluid?

I heard somewhere that the blue tube typically runs hotter, and the cooling fluid clouds up and eventually degrades the image. Replacing the fluid is not trivial but a lot easier and cheaper than replacing and aligning the tubes.

I d> However, I have noticed one problem with the picture: after the set has

If the coolant is contaminated you get cloudy splotches normally and it doesn't change as it warms. I would agree with the other diagnosis that the blue tube has gone weak, though it wouldn't hurt to have the emission checked as it's possible there's something else wrong. It also may be possible to reduce the brightness of the other tubes to get a decent white balance without the blue clipping.

You could try boosting the blue gun emissions by zapping the cathode - grid with a high voltage arc, that procedure has been discussed here many times. It is a temporary fix, and there is always the risk of actually reducing the emissions, but I would guess it works about 85% of the time for a period of 6 to 12 months.

H. R.(Bob) Hofmann

Thank you!

Curious: why would *lower* emission result in bright blue color blotches? Intuitively it would seem that lower blue gun emission would result in an overall yellowish screen.

Thanks again for taking the time to answer.

Thanks for that suggestion.

Think I'll leave it alone though.

It seems to go away after a few minutes and the picture looks pretty decent afterwards (especially for a big screen that only cost me the price of the service manual.)

Thanks again.

Thanks for your reply.

Interesting idea. I've only noticed the effect at vertical light-to-dark edges, though...the rest of the picture looks fine. Cheers.

Thanks for replying.

WB is OK, I just get the bright blue splotch that goes away after a few minutes.

Interesting: the emissions can be measured? Is that done via an equivalent current measurement?

Regards...

Whoops, I thought that Google would put my replies in the right places...sorry.

You put a micro/milliammeter in series with each of the cathodes and urn on the guns one at a time, or there are tube checkers that can do the same thing. Another possibility is to raide the filament voltage of the blue crt slightly to raise the emissions. Depending on the set, you can add a few turns of wire to the horizontal output transformer (HOT) and put them in series with the filament voltage if it is derived from the HOT, measuring the voltage as you add the turns. IF you get the connection so that the voltage decreases, you must reverse the connections. A lot depends on how familiar you are with tv set guts.

H. R. (Bob) Hofmann

Yikes, no not the HOT, you put a few turns of wire around the core of the flyback transformer. Tricks like this and rejuvenating the guns are generally not advisable on projection CRTs though, they're already run very close to their limits and trying to get more life out of a tired one usually just kills it.

JIm:

You can put a few turns around the Horizontal Output Transformer(HOT) core, that is the same as the flyback transformer unless terminology has changed in the last few days. . I have done this a number of times, frequently adding a resistor in series with the added turns to ease the turn-on surge due to the low filament resistance when cold. It prevents a sudden burn-out on turn-on, but like you say it's of limited value and I only do that as a last resort.

Bob Hofmann