21CT55 #2628 restoration

[wiseguy]

123

[miniman82]

The CTC-2/B chassis are unlike any other that came after, as far as alignment goes. There are many more stages, so more things that can go wrong. I would not recommend attempting an alignment on this thing unless you REALLY know what you're doing. When I got my CT-100, it was all out of whack. I tried doing an overall response on of it, but it was no use. I ended up peaking each IF stage by itself, then doing an overall response curve to touch things up. The B&K rig really helps out on that. Still took me over 2 weeks...

[Zenith6S321]

Originally Posted by miniman82

I would not recommend attempting an alignment on this thing unless you REALLY know what you're doing.

Gulp.. Wish I new that earlier. I replaced a bunch of bad resistors in my tuner yesterday and this afternoon began the audio and picture IF alignment process. So far I have only gotten through the audio and 5th video alignment. My sweep generator is acting flakey, but I did manage to get the alignment to match the fig. 15 5th IF response sweep plot. There are markers in the dips are 41.25 and 47.25 MHz. There is a marker at 42.17 and 45.75 in the high gain area. The other marker-like stuff must be from having the 5th IF bottom and top covers off, I guess. Guess I'm committed at this point. I have only aligned three B/W set so far, so its trial by fire for me on this..

Dave

[Zenith6S321]

After two attempts and hours of tweaking I have working set. Nick was so right, the CTC2B is very tough to align, at least for me. Here is a picture of the sweep response from the tuner crystal to the video detector test point. Not as high a peak at 41.65 as RCA shows but the others freqs are not bad. I ended up using the Sencore VA62 10 freq multiburst to do the video traps and bandpass alignment. And I finally realized my color bar generator needs alignment. So please ignore my info on the RCA to VA62 color comparison. I used a Heathkit IO-101 I picked up at this years ETF convention to get the correct color bars to do the color alignment. Here are also some pictures of my flyback temperature using a fan to keep it cool and leaving off the corner cover as a vent. The fan keeps the flyback just warm to the touch after running for hours at about 205mA. And a pic of some cartoon color.

[Zenith6S321]

And here are some Wizard of Oz pictures.

[Zenith6S321]

I still need to find the source of a white vertical line that moves horizontally as I adjust the horz hold control. The line does not go away when I adjust the H drive. Any ideas? I do not have a metal screen to cover the opening under the chassis, could it be due to that?

[old_tv_nut]

Originally Posted by Zenith6S321

I still need to find the source of a white vertical line that moves horizontally as I adjust the horz hold control. The line does not go away when I adjust the H drive. Any ideas? I do not have a metal screen to cover the opening under the chassis, could it be due to that?

It looks like it could be something during retrace not being blanked - does it move the opposite direction of the picture as you turn the horz hold?

[Zenith6S321]

As I rotate the H hold counter clockwise the image moves slightly to the left and the white vertical line moves to the right. So, I think it does what you described.

[old_tv_nut]

Originally Posted by Zenith6S321

As I rotate the H hold counter clockwise the image moves slightly to the left and the white vertical line moves to the right. So, I think it does what you described.

Yes, definitely a sign of something in the video during retrace. Does the visibility increase when you turn the brightness up? Can you see the h sync then? This would mean there's insufficient retrace blanking. (Not familiar with this schematic, so don't know what provisions there may be for blanking.)

[wiseguy]

123

[Zenith6S321]

Originally Posted by old_tv_nut

Yes, definitely a sign of something in the video during retrace. Does the visibility increase when you turn the brightness up? Can you see the h sync then? This would mean there's insufficient retrace blanking. (Not familiar with this schematic, so don't know what provisions there may be for blanking.)

Yes increasing the brightness does increase the brightness of the white vertical line along with the background brightness. If I lower the brightness so the whole screen just goes dark I can still see the vertical white line as shown on a couple of previous pictures. I could not see anything else, so I guess I do not see the h sync. With the brightness all the way up I do see some slanted retrace lines (like on the 40's BW sets), but they go away just under full brightness. Here is a screen capture of the SAMs showing the vertical blanking signal on the cathode of the CRT. My scope shows the 15V pulse riding on a 142V DC level.

[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...

[miniman82]

Mine actually has faint banding when showing blank video, I think it's horizontal ringing. Must be something with the design of the chassis, because the CT-100 doesn't do that.

[Zenith6S321]

Originally Posted by miniman82

Mine actually has faint banding when showing blank video, I think it's horizontal ringing. Must be something with the design of the chassis, because the CT-100 doesn't do that.

Yeah sure seemed like that to me. With blank video I put a 1500pF cap across the 1st video amp and that got rid of it. I put the cap across the 2nd IF and the vertical white line came back. So I figured the noise/ringing was getting in there somehow. Or may it is my alignment.

So after being bummed about that for a while, I realized I have been feeding all my video to the 21CT55 through my DVD player and then through a cheap RF modulator. This has worked just fine for my 1940s BW sets for quite a while. Even my VA62 test patterns were going into the DVD video input to get to the set. I decided to try feeding a blank video from my VA62 through its RF output. The vertical white line was gone!

So my vertical white line has been in the RF I was feeding it, not in the set. I know that does not make sense if I could put a cap across the 2nd IF and have it come back, but the line is not there when I drive it with the VA62, so yippee, I hope.

What is the best RF modulator to feed signals to a 21CT55?