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Old 06-09-2018, 03:18 PM
ThePlague ThePlague is offline
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RCA Victor 21-T-8205 White line in middle of picture

Hello all, thank you for the help providing awhile back on this set! It has had a full recap and is working like a champ. I've been able to run it for 4-5 hours continuously without any issues other than the occasionally user control adjustment. The one thing that is persistent before and after the re-cap is the white line in the middle of the picture. It is more noticeable in images with lots of blacks or darker colors. It moves with the horizontal hold adjustment as well. Is this a fixable issue, or just something to get used to given the age of the set? I'm not certain what it is called specifically, so googling hasn't given much insight. Thanks again!
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Old 06-09-2018, 04:06 PM
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Did you adjust the horizontal drive according to the service manual?

http://www.earlytelevision.org/pdf/r...202_manual.pdf

jr
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Old 06-09-2018, 04:13 PM
ThePlague ThePlague is offline
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I believe I did, but I will go back and re-do the procedure. Do you know what is meant by the term "motorboating" in the service manual?
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Old 06-09-2018, 04:24 PM
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The line on screen looks like what is called a horizontal drive bar.
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Old 06-09-2018, 04:36 PM
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Quote:
Originally Posted by ThePlague View Post
I believe I did, but I will go back and re-do the procedure. Do you know what is meant by the term "motorboating" in the service manual?
Motorboating is a term usually applied to audio circuits. It is caused by a low-frequency oscillation coupled through the power supply, and sounds like a motorboat. You would notice it right away if it happened.

https://en.wikipedia.org/wiki/Motorboating_(electronics)
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Old 06-09-2018, 09:01 PM
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I had a Motorola with a drive bar similar to that; with careful adjustment of horiz drive & horiz hold & could make it better but never made it completely go away. In my case I suspect there was some capacitor in the circuit that was a little off.
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Old 06-10-2018, 11:02 PM
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It does not appear to be a horizontal drive line. The line is most likely due to insufficient horizontal retrace blanking. During horizontal retrace there may be a positive overshoot of the rear of the sync pulse.

If it was a drive line, horizontal scan linearity would be affected with evidence of picture foldover across the line. I see no evidence of this in your photos.

To confirm, adjust the horizontal sync phase by adjusting the horizontal hold control. If the line moves, it is due to a blanking problem. If it stays fixed, it is a drive line.

You should be able to minimize it by adjusting the fine tuning. But there are means to improve retrace blanking if that is the problem which I believe it is.

Last edited by Penthode; 06-10-2018 at 11:13 PM.
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Old 06-11-2018, 12:18 AM
old_coot88 old_coot88 is offline
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Penthode's 100% correct.
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Old 06-11-2018, 01:11 AM
ThePlague ThePlague is offline
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Quote:
Originally Posted by Penthode View Post
It does not appear to be a horizontal drive line. The line is most likely due to insufficient horizontal retrace blanking. During horizontal retrace there may be a positive overshoot of the rear of the sync pulse.

If it was a drive line, horizontal scan linearity would be affected with evidence of picture foldover across the line. I see no evidence of this in your photos.

To confirm, adjust the horizontal sync phase by adjusting the horizontal hold control. If the line moves, it is due to a blanking problem. If it stays fixed, it is a drive line.

You should be able to minimize it by adjusting the fine tuning. But there are means to improve retrace blanking if that is the problem which I believe it is.
I haven't had a chance to open it up and make adjustments per the service manual yet, but I can confirm that the line moves left or right in accordance with the user control of the horizontal hold.
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Old 06-11-2018, 06:54 AM
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There are no adjustments necessary unless you check the RF/IF alignment. The horizontal drive adjustment, if the set has one, will make no difference.

What may be useful to post the schematic of the horizontal sweep/ video amplifier section to see if there is a blanking circuit present.

It may also be due to RF radiation of the horizontal retrace spike being picked up by the tuner. It may help selecting another channel to feed the set. It also may help to move or shield the wires leading to the deflection yoke.

Other things to consider are consumer box sync generators which exhibit too fast a fall and rise time. You may wish to try another set top box. Also alignment of the IF where the video carrier is to low on the Nyquist slope or a faulty IF tube (check by substitution one-by-one ensuring the original is replaced in its original socket).
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Old 06-11-2018, 10:59 AM
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Very interesting, certainly explains those stubborn "drive bars" that cannot be adjusted out by the usual horizontal drive adjustment. I posted a link to the schematic in post 2 of this thread... do you see a horizontal blanking circuit?

jr
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Old 06-11-2018, 02:25 PM
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I reviewed the schematic. There is not horizontal retrace blanking only vertical blanking. This means that a negative going pulse is accompanying the video to cause the line.

I see that there is a common Horizontal sweep- video amplifier 100uF electrolytic across the +260v B+ line. I would put a scope probe across it to ground and see if the if a negative pulse dip is be coupled back to the video amp plate circuit.

It could be the pulse is picked up by the antenna. If you switch the rf modulator to another channel, does the line go away?

Look at the sync pulses of the set top box. If you try another set top box, does that remove or subdue the line?

As to experiment to remove it, I might try wrapping a few turns of one end of an insulated wire around one of wires leading to the horizontal deflection coil leads and connecting the other to the CRT grid. This would effectively couple the retrace pulse to the grid to cutoff the tube. This may take a bit of experimentation and polarity is important so you would have to try each lead.
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Old 06-11-2018, 03:13 PM
ThePlague ThePlague is offline
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Quote:
Originally Posted by Penthode View Post
It could be the pulse is picked up by the antenna. If you switch the rf modulator to another channel, does the line go away?

Look at the sync pulses of the set top box. If you try another set top box, does that remove or subdue the line?
Switching the channel provides no improvement nor does switching the box as I have run it through both my S-VHS player and Betamax player, both exhibit the same issue.

Quote:
Originally Posted by Penthode View Post
As to experiment to remove it, I might try wrapping a few turns of one end of an insulated wire around one of wires leading to the horizontal deflection coil leads and connecting the other to the CRT grid. This would effectively couple the retrace pulse to the grid to cutoff the tube. This may take a bit of experimentation and polarity is important so you would have to try each lead.
This will take some looking into as I have not experimented much with what you suggest. By the CRT Grid, are you referring to the control grid portion of the CRT?
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Old 06-11-2018, 03:50 PM
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As it doesn't change with tuning, it's some baseband pulse in the video/CRT.
Also, you said the H drive adjustment doesn't fix it.

There are probably dozens of small ways this can occur.

I see this set uses PC boards. It may be worth checking all grounds on the IF, Video, Horizontal (and who knows where else). The horizontal output current and voltage is hundreds of times larger than the video signal, so even a small amount of it can be visible. Also as mentioned, try lead dress. Take any of the flying leads and move them around to see if it makes a difference. Make sure the tuner/IF cable is solidly grounded.

When this kind of thing showed up in a chassis design, the engineers would try random extra grounds and variations in lead dress until they found the fix. Any of those fixes could be disturbed over time by repairwork or grounds going bad.
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Old 06-11-2018, 05:25 PM
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As Wayne suggests, a bad circuit board common ground connection to the chassis could well be it. As it is a baseband video problem it would be well to check the lead dress and the soldered grounds especially around the video amplifier. And wouldn't hurt to examine the decoupling-bypass capacitors around the video amplifier e.g. screen bypass and even the 100uF cap on the +260v line.
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