Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Television Broadcast Gear

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 02-03-2016, 04:18 PM
Ralph S Ralph S is offline
VideoKarma Member
 
Join Date: Jan 2008
Posts: 153
TK-31B has horizontal scan problem

I'm working on an RCA TK-31A which was upgraded to a 31B by the station which previously owned it. I've completely recapped the chain: Camera, CCU and Power Supply and am getting potentially good pictures; everything is working fine with the following exception: the horizontal scan has the following problem: The right half of the picture is correct. However, from approximately the center of the picture and going about 4/5ths of the way to the left, there is a sharp demarcation and then expanded sweep width to the last 1/5 of the picture which is a mirror image of the previous 1/5 of picture which was in correct orientation. I know this sounds like a shunt cap failure in the yoke of a CRT receiver from the 40s and/or 50s, but there are no caps shunting the horizontal deflection windings in this camera. Has anyone out there run into this problem before and if so, how did you correct this problem? All replacement parts are brand new and everything remaining in the horizontal section reads "good." Any ideas?
Reply With Quote
  #2  
Old 02-14-2016, 12:18 PM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
Can you post a picture of the distortion? Also posting the schematic diagram portion of the horizontal sweep would help.

I assume the distortion is on the video output and not just the viewfinder?
Reply With Quote
  #3  
Old 02-14-2016, 01:12 PM
Ralph S Ralph S is offline
VideoKarma Member
 
Join Date: Jan 2008
Posts: 153
Thanks for your response. It will take me a few days to get you the picture and tag the different portions of distortion. I'll try to make the fault as clear as possible.
Reply With Quote
  #4  
Old 02-16-2016, 01:16 PM
Ralph S Ralph S is offline
VideoKarma Member
 
Join Date: Jan 2008
Posts: 153
Attached are two pictures taken off a screen showing the standard setup chart for the era of this TK-31. The numbers show the placement of the various geometric sections of the image from the camera. Disregard the various shading errors. They come from a tired IO and in Sections 2 thru 4 represent distinct shifts in gain caused by the distorted sweep which is the subject of this inquiry.

Section 1 is correct geometry.

Section 2 is highly distorted but can be altered but not corrected by adjustment of the horizontal linearity control.

Section 3 is extremely compressed.

Section 4 a mirror image of Section 3.

A large drawing of the camera's schematic is also attached.
Attached Images
File Type: jpg DSCF3053 VK bg1.jpg (90.7 KB, 37 views)
File Type: jpg DSCF3053 VK bg with numbers.jpg (93.8 KB, 37 views)
File Type: jpg TK-31A Camera Schematic final 24x31lo res.jpg (143.0 KB, 32 views)
Reply With Quote
  #5  
Old 02-16-2016, 01:34 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
I am not familiar with these, so can only take a guess.

Is it possible the capacitor on the horizontal centering control is open?

Can you post a higher resolution schematic? Impossible to read plug/socket pin numbers, so I hope I am tracing from the horizontal coils to the circuit correctly.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
Audiokarma
  #6  
Old 02-18-2016, 02:12 PM
Ralph S Ralph S is offline
VideoKarma Member
 
Join Date: Jan 2008
Posts: 153
OK, here's just the deflection part of the camera. I hope this makes it easier to figure out.
Attached Images
File Type: jpg TK-31A Cam. Hor. Deflection Schematic 8x25.jpg (36.7 KB, 28 views)
Reply With Quote
  #7  
Old 02-18-2016, 02:47 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 Ralph S View Post
OK, here's just the deflection part of the camera. I hope this makes it easier to figure out.
Still quite blurry, but I would check all the caps, starting nearest the deflection coils and working backwards (to the right).
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #8  
Old 02-18-2016, 02:59 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
I see a spark gap on the yoke. Could that be sparking over for part of the scan throwing off the linearity etc?
__________________
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
  #9  
Old 02-18-2016, 03:05 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 Electronic M View Post
I see a spark gap on the yoke. Could that be sparking over for part of the scan throwing off the linearity etc?
I think any sparking would produce an erratic tearing as it changed from line to line. This is some sort of ringing in the sawtooth sweep. That's why I suspect one of the caps that is supposed to tie one end of the deflection coil to a constant DC may be open.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #10  
Old 02-19-2016, 12:52 AM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
ll isn't clear to me from where you are viewing the picture. Are you looking at the camera output on a separate known good monitor or is the image taken from the camera viewfinder?
Reply With Quote
Audiokarma
  #11  
Old 02-19-2016, 01:10 AM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
It looks to me as if the damper is not doing its job.
After retrace, the 6BG6 will be switched hard on to effectively dissipate the energy stored in the deflection coils. The left hand side of the image shows severe ringing which suggests the damper is not working.

I would check/substitute the 6BG6 damper and check the waveforms around it on a scope. If R19 is open, I would expect the result you observe.
Reply With Quote
  #12  
Old 02-25-2016, 01:26 PM
Ralph S Ralph S is offline
VideoKarma Member
 
Join Date: Jan 2008
Posts: 153
First of all I want to thank you for your suggestions. I have nailed the problem, but I'm not sure where I'll find a fix. Here 's the reason for the bad Horizontal scanning:

The Horizontal output transformer (T4 - see the drawings I've posted above) has three windings: Main output, horizontal driver and horizontal damper. The horizontal damper winding is wide open - no resistance can be measured from 0 to 200 megs. So... the transformer is kaput!

The obvious solution is to replace the transformer. Here are the RCA IDs: Drawing #629923-501 and Stock #95468 and one of these numbers may be printed on the transformer case. If anyone has one of these that measures right, I'd sure like to get my hands on it! In today's world they probably make a superior door stop or for silencing your noisy neighbor, but I need it for its original intended use! Any help would be greatly appreciated.
Reply With Quote
  #13  
Old 02-25-2016, 01:53 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
One person you might contact is Chuck Pharis:
http://www.pharis-video.com/
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #14  
Old 02-25-2016, 08:27 PM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Kitchener/Waterloo Ontario Canada
Posts: 1,059
You also might try removing the transformer and closely examining it. Possibly the connections to the winding may have broken. The transformer may be salvageable.
Reply With Quote
  #15  
Old 02-28-2016, 04:04 PM
Ralph S Ralph S is offline
VideoKarma Member
 
Join Date: Jan 2008
Posts: 153
Just so everyone knows what I've been talking about, here's a shot of the transformer, T-4.
Attached Images
File Type: jpg Transformer T-4 with arrow.jpg (122.9 KB, 32 views)
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 07:25 AM.



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