Possible delay line problem?

[droptop]

My CTC 7 has developed a slight case of ghosts. The set performs well in all respects except for a slight shadow to the right of the image. It’s reminiscent of the need to adjust the rabbit ears to clear it up. This isn’t the case however. Signals from a directly connected DVD player or over the air via a B-T modulator give the same result. Could this be caused by a defective delay line? Resistance through the line is approximately 100 ohms but from the ground connection to either end of the line shows a resistance of 1400 ohms.

I know there is a capacitance present but there should be no resistance between the coil and shield if memory serves. The horizontal, vertical sync and color are good. The AGC voltage is set to 10 volts P-P but see saw’s roughly 1-2 volts either side depending on scene content. This I don’t remember much about because AGC troubles were rare in my service experience which dates back to the early 70’s working on sets of this vintage that were still in use. Anyone have any ideas or opinions?

[Penthode]

Could you post a photo of a screen shot?

[old_tv_nut]

Posting a picture would help.

Without seeing a picture:
Before blaming the delay line, you might want to check any peaking coils associated with it to see if they have opened; also check resistor values in that area. Also, check coils associated with the video detector.

[Penthode]

Does the ghost change with adjustment of the fine tuning? If so, the problem could be in the video IF. A bad decoupling capacitor could upset the IF response.

[Don Lindsly]

A defective delay line will cause the color and B & W images to not register. The delay line only affects B & W video. If the fine tuner affects the ghosts, it is more likely a defective mixer or IF tube. If the fine tuner does not affect it, look for a mismatch in the antenna circuit.

[old_coot88]

A ringing/'ghosting' symptom can be caused by a bad last IF tube. Try subbing that tube for the heck of it.

[miniman82]

Jumper around it if you suspect it, all that will happen is the chromatic information will be offset from the monochrome part of the picture. Might be difficult to pick out if there's ghosting going on in that state, but you should still be able to see it.

[droptop]

Thanks for all the input. I didn’t get a screen shot before dismantling the set to clean a noisy pot so I can’t post one at the moment. The fine tuning doesn’t affect this symptom at all.

I’ve checked the peaking coils and all are good except L17 (series peaking coil) feeding the video output tube grid which is open. Specs are 11 ohm coil at 250 microhenries wound on an 8200 ohm resistor.

I’m not familiar with their exact function but is it possible to rewind these or do I stand a better chance of finding a good replacement?

[miniman82]

Replace that coil, try it again.

[droptop]

I replaced the oscillator and 3rd video IF tubes and for kicks wound an 11 ohm coil around an 8.2K half watt resistor and installed it in place of L17. None of these changes seem to make any difference. The screen shot below shows the defect. I am going to pull the chassis again and check the video detector circuit for abnormalities tomorrow.

[old_tv_nut]

I'm afraid it's hard to tell from the photo. It's generally blurry and shows some misconvergence. Not sure if the blur is your set or the camera focus.

Are you talking about the faint ghost that's about 1/2 the width of the tie, to its right? This looks wide enough that it might be a reflection in the delay line due to mistermination. How does the series 1800 ohms and 180 microhenry that loads the delay line look?

[old_tv_nut]

I enhanced the contrast to show the wide ghost plainly

[miniman82]

Ditto on the termination, looks like Y line ghosting.

[walterbeers]

Yes, a delay line will definitely cause the problem. I ran into this once on a CTC9. One way to check it is to throw a jumper lead across the delay line and see if the ghosting disappears. Of course the luminescence and color won't match up, but the ghosting will be gone. If the ghosting is gone, the delay line is the culprit. Probably shorted turns in the line itself. Just match one up from a similar set and replace it.

[kramden66]

I'm having a similar problem with my admiral ctc-12 clone , perhaps my delay line let go ? how did you make out with yours ?

mike