Resolution lines on Zenith roundie

[iong]

I have 2 Zeniths. One is a 26kc20 and the other is a 25cm33. Both seem to have picture tubes with good emission that can go bright. however if the picture is set to a good brightness I see the Horz retrace lines near the top. I tried setting the 3 screens once to med. brightness as some of the manuals say and to very low brightness and I still get those annoying lines. I also have the drive controls low. These are not copy protection lines I can move them a little with the vert hold control. How can I get rid of these? Any ideas anyone.
Thank you,
Perry

[old_tv_nut]

You mean retrace lines.

Just because you can move them with the vertical hold does not tell you if they are copy protection or not.

Assuming that you are correct and they are not copy protection, someone else here may have a suggestion on how to fix them.

If they are copy protection, there also may be a modification to the set that can fix them, OR you can use a device that removes them from the video signal itself. What is your signal source?

Posting a picture would help, I think.

[iong]

Thank you, It's retrace lines. All sources TV, DVD's everything. I's not copy protection. The lines are steady.

[zeno]

Sounds like a blanking problem. Try the tube first ( 6KT8 ? ).
For grey scale on almost any tube chassis set
After warm up service switch to service & off channel.
Bring up one at a time then back off til the line just disappears.
Go back to normal & tweak if needed.

Be sure you can turn down the bright, contrast & color to get
little or no raster. remember these sets were NOT brite. To enjoy the
best pix use in dim lighting.

73 Zeno
LFOD !

[iong]

Yes the 6kt8 was weak and so was the 12gn7 I had good ones and reset the screens and it much better can only see the on blank gray raster. The screens must have been higher yhen normal because of the week tubes and the manual says set all of them to medium brightness. This must be incorrect. Thanks, Perry

[old_tv_nut]

I'm looking at the SAMS 25MC30 schematic from the earlytelevision site, and it appears vertical blanking is a 90 v pulse from the vertical output plate (V10 6HE5 pin 6) coupled through C34 (.015 1kv 10%) and R66 (150k) to the video outut circuit. You might check these components, but it seems a little strange to me that you have the same problem on both sets if their circuits are alike.

The G2 setup procedure, once you have gone through it, should end up with approximately the DC voltages shown on the CRT grids and cathodes. In the setup position, the cathodes are at a fixed standard voltage, and G2's are adjusted to just barely be above cutoff with no color signal and nominal voltages on the grids. If proper cutoff cannot be reached with the G2 controls (due to CRT variation [edit - or demodulator tube variation]), then the grid voltages are adjusted slightly with the CRT bias control so that the cutoff point is within range of the G2's. If you do the setup out of order by accident, you may get the wrong voltages on the CRT. I think this could conceivably affect the blanking action.

[reeferman]

Retrace lines were my specialty.
I could produce them on any set in the shop.

[Yamamaya42]

I may very well have the exact same problem on my CTC-16XL, have always been seeing the same annoying lines at the top and not been able to get rid of them fully.

Have looked and looked at horz blanking area and not found nothing, not really knowing that the vert blanking was tied as mentioned, to the plate of video output, in my case they are a .01 cap and 2 res, 100k & 68k, and have not been looked at very closely yet, i'm in no big hurry to yank it out and check, cause its just an annoyance at this point.

[Yamamaya42]

the more i look at it, the more likely i think it's my problem as well

https://imgur.com/ZH3uckS
r71 WAS replaced on mine, but70 is on the sweep PCB and was overlooked, and c31,is status unknown.
this is very well the source of my retrace problems and the same sort of thing for iong

[bgadow]

Originally Posted by reeferman

Retrace lines were my specialty.
I could produce them on any set in the shop.

[bhegges]

Resurrecting an old thread as I am having the same issue as the OP. I have a 25MC33 Zenith Roundie that has been repaired and aligned. Last night I installed a much newer CRT which tested very good. The issue is I get retrace lines on the screen which I didn't have before. I have tried turning down all of the G2 screens, CRT bias, and brightness. I also have tried swapping the 6HE5 vertical output tube but it made no difference. C34 (.015 1kv 10%) was replaced as part of the earlier repair and R66 (150k) had previously tested good.

Thoughts on what to try next?

Here is what I get with everything turned down:

[old_tv_nut]

If you have everything turned down including brightness and contrast, you should have a completely (or almost completely) black picture, not blue.

Don't know enough about this set to conclude what the problem is from this picture, but something's obviously wrong. Are you sure the CRT is OK, with no shorts?

[old_tv_nut]

Looking at the schematic now.

Measure cathode and G1 voltages on the CRT.
Try swapping demodulator tubes (6JH8s) and see if the background color changes.

[zeno]

Keep in mind these sets were never brite. They will never be like
a more modern in-line or LED set. Many try to make them brighter
but that screws things up like retrace lines.

Check the CRT voltages against the Sams. The set with blue & retrace looks
like the blue G2 is set real high. It may have a problem but G-2 is easy stuff.
Just a voltage divider between @250 V & @800 V that is adjustable.
Also look for a brite range, brite limiter or kine bias control. If set to high can give retrace. And if you wish you can post the CRT voltages for comment.

Zeno

[Username1]

.

If your original tube did not do this, then it's possible this tube has a short, you put
the socket on the tube and bent a pin, and it's not making good connection with
socket, or you possibly pulled a wire off somewhere on the chassis, or
accidentally shorted wires from the crt socket somewhere on the chassis.
Carefully look around at everything before you start to go nuts......
Squirrel humor....

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