Issues with my "new" '73 Zenith

[freakaftr8]

Thats what I was thinking as well. Blue bleeding is not a good sign. Do you have access at a CRT tester?

[Jeffhs]

ctc17 said he couldn't see anything other than a white box on the CRT. While looking at that picture I saw a wide blue area at the far right side of that box (looking at the screen from the front of the set), so there is a problem with the blue convergence (I don't think it is simply blue bleeding out from the raster, though without a picture it's hard to tell). Flip the service switch to the service position and you will probably see the blue line separated from the other two lines; this is a dead giveaway that the convergence is off. However, a program picture will show beyond the shadow of a doubt that there is a convergence problem. If blue is as far off as it seems to be with a white raster, it will stand out like a sore thumb on an air, cable or DVD/VCR signal.

[old_tv_nut]

NO, definitely not convergence. A convergence problem would make the left side of the white square yellow at the same time as making the right side blue. Definitely a blue video drive problem.

[jr_tech]

Originally Posted by ihmeyers

The owner demonstrated it for me at his house and it had a really strong picture and the colors looked good. When I got it delivered yesterday I notice the greyscale was way off (much too blue).

I would find it difficult to believe that the blue gun of the CRT went bad in such a short period of time...It looks to me like there is a circuit problem with the blue gun drive circuit or related power supplies that causes the response to have a long "hang time" or slow "fall-time". Rise-time looks ok, as the leading edges of the picture look sharp, but it appears that once the blue is turned on, it is slow to turn off. Do you have a 'scope?

Agree, this is not a convergence problem. I am guessing that a resistor or capacitor in the blue drive circuit broke or shook loose on the way home.
jr

[old_tv_nut]

Originally Posted by jr_tech

I would find it difficult to believe that the blue gun of the CRT went bad in such a short period of time...It looks to me like there is a circuit problem with the blue gun drive circuit or related power supplies that causes the response to have a long "hang time" or slow "fall-time". Rise-time looks ok, as the leading edges of the picture look sharp, but it appears that once the blue is turned on, it is slow to turn off. Do you have a 'scope?

Agree, this is not a convergence problem. I am guessing that a resistor or capacitor in the blue drive circuit broke or shook loose on the way home.
jr

Me too, except that if this is blue drive to the *cathode*, switch "rise" and "fall." A video output transistor driving the cathode pulls it downward to turn on the gun, and if the transistor is driven into saturation, this is what it looks like - turn off from saturation is very slow. In a normally operating set, you don't get into saturation, although some sets designed to loose tolerances would let the customer saturate the color with the strongest drive (usually red) by turning the contrast or "picture" control too high.

[ihmeyers]

after playing here for a week the set is no worse/no better. As long as contrast & brightness are down there isn't much bleeding. It's at its worst when there is a very bright white on the screen. Other than that it is OK and like DaveWM suggested to me, the set is definitely growing on me.

I think a cap might be going bad in the radio section as that will get "spitty" (like a sputtering tube) every so often but that's a whole other issue.

[freakaftr8]

You can of course do the wiggle test with wires, connections, modules, etc... to see if the blue smear goes away. Also, turs the contrast/picture down all the way, turn brightness up all the way. Is the smear still there?

[DaveWM]

Be real careful in there, I got into some tripler voltage or deflection power and fried some muscle in my arm, still not right 8 months later.

[old_tv_nut]

Do you have a schematic for the video section?

[JB5pro]

Originally Posted by DaveWM

Be real careful in there, I got into some tripler voltage or deflection power and fried some muscle in my arm, still not right 8 months later.

That is good advice. I had no idea that much damage could happen from TV high voltage. I have had voltage arcs from some older sets that left a fried little spot on my finger ike less than 1/4" in diameter. I sometimes wondered if a jolt or two could actually be good for the system somehow. Is it possible that electrical shocks that do not actually fry much inside or outside the body could have any beneficial effect?