Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Early B&W and Projection TV

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 06-09-2018, 03:18 PM
ThePlague ThePlague is offline
VideoKarma Member
 
Join Date: Apr 2017
Location: Colorado
Posts: 60
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!
Attached Images
File Type: jpg image1.jpg (86.0 KB, 84 views)
File Type: jpg image2.jpg (55.2 KB, 95 views)
Reply With Quote
  #2  
Old 06-09-2018, 04:06 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 4,510
Did you adjust the horizontal drive according to the service manual?

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

jr
Reply With Quote
  #3  
Old 06-09-2018, 04:13 PM
ThePlague ThePlague is offline
VideoKarma Member
 
Join Date: Apr 2017
Location: Colorado
Posts: 60
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?
Reply With Quote
  #4  
Old 06-09-2018, 04:36 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 7,184
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)
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #5  
Old 06-09-2018, 04:24 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
The line on screen looks like what is called a horizontal drive bar.
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
Audiokarma
  #6  
Old 06-09-2018, 09:01 PM
bgadow's Avatar
bgadow bgadow is offline
VideoKarma Member
 
Join Date: Oct 2003
Location: Federalsburg, MD
Posts: 5,814
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.
__________________
Bryan
Reply With Quote
  #7  
Old 06-10-2018, 11:02 PM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
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.
Reply With Quote
  #8  
Old 06-11-2018, 12:18 AM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Penthode's 100% correct.
Reply With Quote
  #9  
Old 06-11-2018, 01:11 AM
ThePlague ThePlague is offline
VideoKarma Member
 
Join Date: Apr 2017
Location: Colorado
Posts: 60
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.
Reply With Quote
  #10  
Old 06-11-2018, 06:54 AM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
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).
Reply With Quote
Audiokarma
  #11  
Old 06-11-2018, 10:59 AM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 4,510
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
Reply With Quote
  #12  
Old 06-11-2018, 03:50 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 7,184
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.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #13  
Old 06-11-2018, 05:25 PM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
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.
Reply With Quote
  #14  
Old 06-12-2018, 10:05 AM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 7,184
I don't think the added grid pulse is a treatment for a drive bar, which, if I understand correctly, occurs during trace, not retrace. The grid blanking pulse acts during retrace.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #15  
Old 06-12-2018, 01:47 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 7,184
Quote:
Originally Posted by ThePlague View Post
It moves with the horizontal hold adjustment as well.
Does it move more than the picture and in the opposite direction of the picture, when you turn the horizontal hold? If it does, that indicates it's happening during horizontal retrace, so not a drive line.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 05:07 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.