CT100 owner request

[dtvmcdonald]

Its NOT out of sync. When its wrong its in sync, quite tightly.


The problem clearly is that it is in sync to the AVERAGE of the
color burst and the part of color in the left hand edge of
the image. You can see this easily on the scope when
doing the Fig. 34 test. Different color give different effects.
If the field color is in phase with the burst, it gets longer.
IF out of phase, it gets shorter. In these cases the color on the screen stays OK.
If its 90 degrees out, it gets longer and you can see it change
phase during itself, on the scope.

In other words, the gating signal is too long or too late.

The effect is RARE on ordinary program material. It is
sometimes seen on football games where there is lots of green
at the left edge, and always on commercials with solid saturated color backgrounds.

I suppose I should check the tuning of 2L141 and 2T122 again.
What I'm really looking for is confirmation that my set is off,
that its not a design problem. It could be a problem with a
capacitor or resistor in that area, making the gate be too long
or too late.

[Pete Deksnis]

Originally Posted by dtvmcdonald

What I'm really looking for is confirmation that my set is off,
that its not a design problem.

Last May at the ETF convention I gave a PowerPoint presentation about the final tweaking that took place before the CTC2 was released for initial production. I had a sidebar that had a screen shot of an anomaly that is similar to that in your post, and I asked the same question you have, but at that time left it hanging without an answer.

Since then I'd troubleshot the problem, and to get right to the point, yes, I think there was a design problem. Highly saturated chroma that appears a few microseconds in from the beginning of horizontal sweep does not cause the anomaly, because it occurs far out of range of the keying pulse trailing edge.

Highly saturated chroma, which appears right at the beginning of the horizontal sweep, occurs close enough to the keying pulse trailing edge to literally climb up the edge of the pulse, slide onto the top of the keying pulse, and infect the color burst with chroma. This anomaly can occur because rotating the horizontal control varies the phase of the horizontal oscillator enough to shift the timing of the keying pulse -- and drive it into the garbage chroma signal.

Why garbage? Because the color burst is tapped from the plate of the 6CL6 first video amplifier by a tiny (3 pF) cap that can't help conducting some of the chroma signal as well. (Of course, if there is no chroma there is no chroma signal, which is why, if there is white or black at the beginning of the horizontal sweep, there is no chroma to contaminate the color burst at the top of the keying pulse, and the anomaly under discussion does not and can not take place.) Only highly saturated chroma signals cause the anomaly because only large signals will be great enough to get through the 3-pF coupling cap in sufficient amplitude to cause color burst contamination.

Another quick point: I believe Philco, when designing its first color TV, the Model 22D5102 with the TV 123 chassis, ran into the same problem as RCA with its CT-100. Philco's fix was to add a pot to the horizontal oscillator circuit that was adjusted to limit the range of the horizontal hold control.

I have been fleshing out that ETF PPT video; when finished I will try to make it available if there's interest.

Of course, there's still the chance that it's an alignment problem... but I'm beginning to believe not.

Pete