Predicta vertical ghost line

[ShartZenith]

This week I've been running the Predicta on the kitchen table every night to monitor its little quirks and problems so my friend and I can hopefully iron them out. One I've noticed is a faint, ghost-line that runs almost vertically through the middle of the screen on all channels. See photo attached. I caught it between screen changes and its a lot easier to see. Any help is appreciated. Thanks!

[old_coot88]

Does the line change position (left/right) if you bump the horiz hold in both directions? Or does it stay in a fixed position regardless of the H hold setting?

[Electronic M]

That is probably a horizontal drive line. Adjusting the horizontal drive, width and linearity controls should fix it. Though I recall someone else with a Predicta found that it was a video ringing issue on their set and required adding a capacitor to minimize it.

[ShartZenith]

By adjusting the horizontal dial the line moves both directions almost off the screen. What does this mean?

[Don Lindsly]

That set does not have a horizontal drive or linearity control. The width control adjusts HOT screen voltage.

The "moveable" line is usually a result of an imbalance or over correction in the horizontal phase detector circuit. The resistors and caps in the feedback network and sync amp plate resistors are the first suspects. Aligning the horizontal oscillator sometimes helps. A model or chassis number would help for more specifics.

It may come and go depending on the signal source.

[old_coot88]

Originally Posted by ShartZenith

By adjusting the horizontal dial the line moves both directions almost off the screen. What does this mean?

It means the line is not originating in the H sweep section (ie., horiz osc or output) but somewhere in the video chain (or possibly in the phase detector).
You might try this.. Put a cap of say, .1 mf/600V from the cathode of the CRT to ground, which will kill the video signal. If the line remains, this will tell you it's not originating in the video chain.
(This is assuming video goes in the CRT via the cathode which is standard practice, rather than G1.)

[Phil Nelson]

For what it's worth, there was a long discussion of this issue on ARF. After a lot of checking & cogitation, I believe the punch line was that this is a characteristic of the design, at least somewhat, and you can reduce the line by adding a small capacitor, possibly at the risk of degrading the audio.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[ShartZenith]

Model H3410, chassis 10L43

[ctc17]

Davewm discovered this was do to poor quality modulators in cable and converter boxes.
The fix was a quality modulator like the BT Modulator. Adding the cap is just a bandade.

The crappy modulators also resulting in lots of buzzing with these old sets.

[Steve]

Had similar (but not identical) problems with the Predicta I'm working on
now. The solution in my case was keeping the wire going to the CRT
cathode away from everything else. Especally the HV cable.
Also, make sure the shielding on your tuner is in place and on
tight. Once again, crud from the wire bundle going to the CRT
got into the tuner causing all kinds of problems. Make sure
your tuner is grounded to the chassis via a sperate metal
strap, which was originally in the set but may be missing in many.
Steve

[Penthode]

I wrote a bit about this earlier. It is indeed caused by cheap modulators. You mentioned the line shifts with the adjustment of the horizontal hold control. The line is caused by ringing in the video chain and the falling edge of horizontal sync overshoot or color burst during horizontal retrace will show up as faint line(s).

A cure is to repair if included, modify or add a horizontal retrace blanking circuit. This would involve coupling a pulse from the horizontal flyback to the video path to the CRT. Often you will find the vertical retrace blanking is included: adding horizontal retrace blanking is somewhat similar.

Another solution as suggested is to get a better modulator or modify the video going to it to minimize the overshoots. Broadcasters years ago were very careful to ensure their video did not cause this problem. With modern sets, less attention is paid to the video because newer sets blank the CRT during horizontal retrace!