color bar bleeding

[DaveWM]

this is my zenith 23xC138, figured I would start a thread to address the color bar issue, pls help. seem the worst around the yellow bar.

[DaveWM]

I will get a better pic in a bit, but I replaced both of the 6EM8 demodulator tubes and its a LOT better.

[ctc17]

every tube color set i have does that to a point with the ntsc style color bars. dont worry about it. the rcas are the only ones that are fairly good at it.

[ctc17]

Look at his bleed here http://videokarma.org/showthread.php?t=250171&page=2

I guess this would explain why the color bleeding on the Simpsons. Tubes sets seem to struggle with yellows. His is better with the yellow but I believe it has a solid state front end and may have the color demod IC

[ctc17]

Im going to correct myself here, that is actually really bad. The yellow. I usually get bad bleed between purple and green.
I looked back through my chroma bandpass alignment videos and the 4.5 trap and bandpass tilt had the most effect on that. One of the coils is bandpass with and the other tilt.
I need to make you a detector probe for your 415 so you can do bandpass alignments. The proper detector probe is a must

[DaveWM]

more pics changing one of the demod tubes had some improvement, but still the you can see the yellow bar has a touch of green like the the whole green portion of yellow is over the the left. on the right side of the yellow its also a bit off, after that it looks pretty good.

[DaveWM]

the last shots and a couple full screens with diff setting for color/bright/fine tune etc..

[DaveWM]

and now the ringing

[ctc17]

Whats up with pink? Thats spost to be a nice purple, red+blue.

The rest looks ok to me, not to bad for a tube set.

Ok let me say magenta before I start getting mail bombs.

[andy]

...

[DaveWM]

viewins is pretty good, on some scenes the bleed will make for a greenish fringe where is does not belong. It shows up more on current broadcast vs. older shows where the use of color seemed more natural.

[wa2ise]

Many TVs use a luma delay line to compensate for the time delay involved with chroma demodulation. This delay line is usually a long pipe shaped coil wrapped with foil, and then insulation. If the far end of this delay line isn't terminated with a correct load resistance, the luma signal can bounce back and forth, producing ringing like what you are seeing. Or produce the mismatch of color vs luma edges on the color bar pattern. They may instead use a "source termination" resistance, or just depend on the output impedance of a cathode follower tube to provide this source termination. The source termination will absorb all of the reflection, and thus not allow it to bounce back to the destination. Maybe a weak tube may not produce the correct impedance to make this happen. Or a drifted resistor.

To be sure it's not a misaligned IF, you could try injecting baseband video where the video detector detects the video off the IF strip. Though TV sets tend to produce a higher voltage amplitude video than that you get from a baseband video generator, so the injected baseband video will look to be low contrast.

Something else to consider: Back in the analog NTSC broadcast era which ended last year, TV station transmitter modulators (exciters) had what was known as "group delay pre-distortion" circuits, to allow for simpler consumer TV set IF circuits. Most consumer TV modulators don't bother with this, and you'd get some ringing, but the one in the Channel Master HDTV converter box CM7000 does do this predistortion. If you have or can buy or borrow that converter box, see if your TV set still has ringing.