21CT55 #2628 restoration

[wiseguy]

123

[Zenith6S321]

Originally Posted by wiseguy

Try a Different H output Tube, and Damper, and if anything maybe see if tuning H waveform Slug changes things

I tried two other H output tubes and 1 other damper tube but could see no difference in the vertical white line. Changing the bottom H osc slug just moves the line left or right.

[Zenith6S321]

I notice that turning the contrast all the way down removes the vertical white line. I can then turn the brightness all the way up with no line.

If I connect the Heathkit vectorscope and use its switches to disable the CRT grid video I do not see the line. Just connecting the vectorscope leads to the CRT grids reduces the white line quite a bit. Maybe high frequency ringing occurring during the horizontal retrace somehow coupling into the video?

I am using three modern 120 mH peaking coils that drive the CRT grids. I tried substituting an old style Miller replacement 120 mH peaking coil, but it shows the same white line.

Maybe I can track it down by putting in caps to filter out the noise at places along the video processing...

[Penthode]

The line I believe is actually due to the other end of the sync pulse. Consider this: the other end of the sync pulse is approximately 4.7us after the horizontal sync trigger. This falls within the active picture in the middle during the horizontal retrace period and if not properly controlled, will induce a vertical white line.

The factors which induce its appearance include IF alignment or video amplifier response in conjunction with the sync generated in a DVD player perhaps having too sharp a risetime. If the overall TV's video response is not reasonably flat, this will cause an overshoot into white which shows up as a white line.

Earlier sets did not have retrace blanking which makes this more problematic. The solution is careful check of the overall video RF and more particularly the IF response.

Color chassis's and the CTC2 chassis in particular is tough to align if you do not have the correct equipment. Fortunately good equipment is available on Ebay at a reasonable price. I trust you will find better equipment.

Forty years ago when I dismissed the thought of ever acquiring Hewlett Packard test equipment to do the job. Back then, at $5K to $10K, 1970's HP equipment was certainly out of the question. In the last 10 years, (thanks to Ebay) I picked up a 1970's HP8601a and HP8600a together for less than $100. I have used these devices to align sets RF, IF and chroma sections to and often I feel more accurately to factory specifications.

Alignment can be tough and is impossible without adequate equipment. But doing it right with the right equipment always rewards your efforts.

Originally Posted by Zenith6S321

I notice that turning the contrast all the way down removes the vertical white line. I can then turn the brightness all the way up with no line.

If I connect the Heathkit vectorscope and use its switches to disable the CRT grid video I do not see the line. Just connecting the vectorscope leads to the CRT grids reduces the white line quite a bit. Maybe high frequency ringing occurring during the horizontal retrace somehow coupling into the video?

I am using three modern 120 mH peaking coils that drive the CRT grids. I tried substituting an old style Miller replacement 120 mH peaking coil, but it shows the same white line.

Maybe I can track it down by putting in caps to filter out the noise at places along the video processing...

[Zenith6S321]

Originally Posted by Penthode

The solution is careful check of the overall video RF and more particularly the IF response.

I put a scope on the video waveform from at the grid of the first video amp and I can see a positive overshoot. Do you find that you have to reduce the high frequency IF response in order to slow the rise time to limit the overshoot?

Dave

[Penthode]

Originally Posted by Zenith6S321

Do you find that you have to reduce the high frequency IF response in order to slow the rise time to limit the overshoot?
Dave

No, I believe it is essential to make the response as close as possible to the factory specification. It may be that way it is currently aligned, the carrier is too low on the "Nyquist" slope to compensate for perhaps the higher video frequencies ("lower IF") rolloff. You can check this as I would suspect the white line will disappear when fine tuning the video carrier up the slope.

I believe the CTC2B chassis with 5 IF stages and the response going down to 21.65MHz AND the sharp transition makes it even tougher to get it right. But it can be done with the right equipment and some practice.

I recall Wayne suggested that is why the later "haystack" IF response became popular: it would get rid of the "galloping ghosts" when fine tuning and perhaps help prevent the white line. But I like the extended IF response design because I imagine if aligned right the picture will be better on a 21CT55 than on the the later CTC4's CTC5's and upward.

Terry

[Zenith6S321]

Originally Posted by Penthode

I believe the CTC2B chassis with 5 IF stages and the response going down to 21.65MHz AND the sharp transition makes it even tougher to get it right. But it can be done with the right equipment and some practice.
Terry

Thanks for the information Terry. I put the VA62 back to "external modulation" and took a look at the video at the first video amp. It did not have any video sync at all, so no sync overshoot, that's why it does not have the white line. I will take another crack at the alignment but this time I will also look at the video waveform as I move the sweep and marker generators through the stages to try to understand which has the most impact on my overshoot problem.