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 Post subject: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 2:09 pm 
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Location: Waukegan, IL
I have faint vertical bars across the entire screen. you can see them when there is no video on the screen or the scene is very light. ive head they could be 3.5mc interference, but i dont think so. when i disconnect the video source from the antenna input, they bars are still there. any ideas? could it be the capacitor across the horizontal yoke coils?

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 3:31 pm 
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Joined: May Sun 07, 2017 11:35 am
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Location: Belrose, NSW, Australia
I think you'll need to post a clear picture....

I suggest one of the whole screen with no video and a close-up as well.

Do you have a scope you can use to see where it's getting in?

No good guessing before measuring!

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 4:17 pm 
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Location: Waukegan, IL
well, you cant get a picture because i dont have a good camera.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 4:35 pm 
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Location: S. Dartmouth MA 02748-1225 USA
If, this is a receiver with PC boards, find all the ground to chassis points and re-solder them. Do the same for any component that goes to ground in the video amp and vertical oscillator. If this is a full chassis receiver, solder the ground rings around the tube sockets, any riveted connection and any soldered connection to the chassis in the same areas as above. Use a solder iron that has a large copper bit so it can throw heat into the chassis. Scratch up the joints with a stainless brush and use liquid solder flux. This often remedies this type problem without advanced techniques. It may dramatically improve contrast if the video amp is the problem.

YMMV

Chas

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 7:38 pm 
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Vertical bars are often drive lines.

One other possibility is it is a radiated RF noise pulse from the horizontal you can eliminate radiated RF as a cause by pulling the video detector of last IF tube. If the noise is still there it is either entering the video later or is not in the video....if the scan speed varies a bit mid scan line then you will get a bright or dark spot (and if it does it in the same point of each line then you get a vertical line).

This is the type of problem to solve with a scope.

Next time you upgrade your phone you could get a smartphone, most have good cameras...heck most pictures I post are taken and posted from my Smartphone.


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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 10:11 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
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Location: New Hampshire
Post the make, model & chassis numbers.
Sounds like either the G-2 A.K.A screen control is set to high or
the CRT cathodes are too low.

73 Zeno
LFOD !


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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 10:17 pm 
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Rca 21D527 from 1955. Its recapped. Recapped with a mix of poly and pp caps since i used the orange drop kit from Just Radios where i bought the caps from. I never been happy with any radio or tv i recapped. Be nice if the proper capacitors were still made. Mainy film and foil and not metalized. And i had to parrallel a few caps in the tv to get the proper value and maybe thats even part of the cause.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Tue 09, 2020 10:42 pm 
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trainman wrote:
RCA 21D527 from 1955. Its recapped. Recapped with a mix of poly and pp caps since i used the orange drop kit from Just Radios where i bought the caps from. I never been happy with any radio or tv i recapped. Be nice if the proper capacitors were still made. Mainly film and foil and not metalized. And i had to parallel a few caps in the tv to get the proper value and maybe that's even part of the cause.
Those are good choices for a TV especially in the vertical oscillator where stability in value is very important.

The poor chassis connection issue is very real to me. I refurbished a Raytheon Belmont in 1985. I used orange and chocolate at the time no China metallized... yet still video was weak despite sweep aligning... Then , poking the chassis with a popcicle stick I saw a slight improvement. Using freeze spray and the soldering gun to cool/heat. I narrowed the issue to the riveted joints. The cadmium corrosion would not let even active rosin flow on the joint, BTW I have a 250 watt American Beauty iron with a 1/4# copper bolt...

I used the tiniest amount of an active flux that flashes off with the heat as soon as it does I feed rosin solder and the riveted joint is smoothed with solder. I did that to all the ground joints and the set came alive.

I made a primitive video of the set and took some pictures of it operating.

I had my one taste of TV restoration, frankly I didn't like it. I sold the set with all other TV related stuff that I had accumulated from 30 years in the TV repair rat race.

If you are unsure about riveted connection, drill it out and replace with hardware using "star" washers to dig into the chassis.

Trying to measure the resistance of such a bad connection is not possible with service instruments.

YMMV

Chas

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Wed 10, 2020 12:39 am 
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Location: Dallas, TX
trainman wrote:
Rca 21D527 from 1955. Its recapped. Recapped with a mix of poly and pp caps since i used the orange drop kit from Just Radios where i bought the caps from. I never been happy with any radio or tv i recapped. Be nice if the proper capacitors were still made. Mainy film and foil and not metalized. And i had to parrallel a few caps in the tv to get the proper value and maybe thats even part of the cause.

Sorry to hear that you have never had a good outcome from your efforts. However I think that your blaming the available types of capacitor is off base. Many have restored radios and TV without problems. Maybe you expect too much from vintage electronics design. Do you have the equipment for adjusting the sets?

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Wed 10, 2020 2:44 am 
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Location: Waukegan, IL
I expect them to work. Dont you think new capacitors have different characteristics than the originals that in some areas of a radio or tv might cause it to not work as designed?
-
Like why am i measuring -9 volts on the grid of the horiz output tube when schematic calls for something like -14 and i have the drive trimmer cranked down beyond tight and the drive line barely goes away? Maybe its that metalized polypropylene cap? Be nice if i could find a polyester film foil caps to use there. Not at 1k rated. I think i can find a 600v film foil.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Wed 10, 2020 3:01 am 
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Location: Belrose, NSW, Australia
Any modern cap will be much closer to an ideal cap than the paper caps it had originally. And much closer to its marked value too.
Stop worrying about this. Your problem lies elsewhere!
It would be an incredibly stupid designer who took advantage of deficiencies of paper caps in his design. It just doesn't happen.

I had an issue with a "drive line" that wasn't a drive line. After first suspecting the Flyback (unobtainium), I did some ring tests with a scope and a function generator. The ring testing revealed a difference in the two halves of the horizontal yoke winding. I eventually tracked it down to a cracked ferrite pole piece in the yoke!

The "drive line" was caused by the core of the left-hand side of the yoke saturating. Reducing the drive (as you are doing) avoided saturating the broken core and the yoke would return to close to normal operation..

Because the yoke was also made of unobtainium, I glued the broken pieces together with epoxy. It helped enough to get an acceptable result.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Wed 10, 2020 5:22 am 
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Location: Ann Arbor, MI
trainman wrote:
I expect them to work. Dont you think new capacitors have different characteristics than the originals that in some areas of a radio or tv might cause it to not work as designed?
-
Like why am i measuring -9 volts on the grid of the horiz output tube when schematic calls for something like -14 and i have the drive trimmer cranked down beyond tight and the drive line barely goes away? Maybe its that metalized polypropylene cap? Be nice if i could find a polyester film foil caps to use there. Not at 1k rated. I think i can find a 600v film foil.

When you reduce the drive the voltage on the grid of the horizontal output tube will go down. If you set the drive trimmer to a more normal tightness you will get the -14 volts the schematic calls for. The voltage is developed by the tube clamping the positive going part of the drive at about zero volts. So the majority of the drive voltage will be negative.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Wed 10, 2020 6:25 am 
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Location: Waukegan, IL
no, i wont. i have the trimmer beyond tight. so tight im practically twisting the entire trimmer off its mount. cant get the value in the schematic at all. at least its still a negative value. maybe the trimmer is bad. i have other trimmers, but the cover a slightly higher range. the less negative the drive voltage is, is where the drive line goes away. yes i have these faint vertical bars, but there is also ONE line that comes and goes when i adjust the trimmer. once i get to about -9 volts, it goes away.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Wed 10, 2020 8:21 am 
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Joined: May Sun 07, 2017 11:35 am
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Location: Belrose, NSW, Australia
Tony I think what Tom is saying is that if you loosened the trimmer you will get a more negative voltage, maybe even the -14 on the schematic. But you will get your drive line back.

We really are going to need to see some pictures we are trying to help you here but flying blind.

Although it is starting to sound like the same issue I had. Does the contrast of the vertical bars vary from one side of the screen to the other?

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Wed 10, 2020 4:09 pm 
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as i recall, i swapped the yoke once, and the problem didnt go away. if it wasnt going to mess up all my centering adjustments, id swap the yoke again, just to confirm.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Thu 11, 2020 2:32 am 
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Tony, when you look closely at the scanning lines, do they have a tiny wiggle in them or are they completely straight right across the raster?

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Sat 13, 2020 3:02 pm 
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If you have (or can borrow) an oscilloscope, check all of the B+ lines and every place in the video circuit with a decoupling capacitor. Everything should be clean, with no signal. It sounds like horizontal pulses are getting into the video somewhere.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Sat 13, 2020 9:47 pm 
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Lets say horizontal is getting onto the video, how do i fit it?

I have a scope, but im not well versed in tvs, so i may not know how to detect a bad waveform.

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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Mon 15, 2020 12:30 am 
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Very often a series of about 8 vertical bars means the color burst is seen during horizontal retrace. A simple a quick fix if you use a DVD player and an RF modulator feeding the set is to use the 'Y' or Luma output of the DVD player instead of the Composite out.

The Y channel is black and white only without the burst and is most suitable when feeding older black and white sets. Y has no burst and will quickly prove whether or not if this is the problem.


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 Post subject: Re: Faint vertical bars on the screen
PostPosted: Jun Mon 15, 2020 1:26 am 
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I stated earlier they dont go away when the video source is disconected.

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