Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Early Color Television

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #16  
Old 02-12-2019, 01:04 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: 4,837
According to the schematic, there should be about 5 volts difference across R154 (260 V on supply side, dropped to 255 V at the plate of chroma bandpass). You could measure the supply and the plate voltage and see if they are 5 volts different. When the color killer operates, the bandpass amp is cut off and there will be no drop.

So, go back to grounding point E. This should defeat the color killer and let the bandpass amp conduct. Turn the color control all the way up and see if you see any color.

As far as using the scope, set the scope sweep rate to horizontal sweep rate (about 10 microseconds per division). For starters, set the vertical sensitivity to 10 volts per division (or 1 volt if you have a 10X probe) and check for presence of all the waveforms shown in the SAMS schematic for the chroma sync phase detector and color killer, plus the chroma bandpass. Set the vertical to higher gain to view the smaller waveforms that are marked about 10 or 12 volts peak to peak.

Do you have a color bar test pattern to use, or are you using some program video? The chroma waveform on pin 3 of coil A14 will generally not be as big and obvious with program material as with a test pattern, but you should be able to see it come and go when the color killer operates.

Also look for the chroma at point G, pin 1 of V23 X demodulator (or pin 1 of V21, Z demodulator).
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #17  
Old 02-13-2019, 02:08 AM
Jon F's Avatar
Jon F Jon F is offline
VideoKarma Member
 
Join Date: Dec 2013
Location: Cupertino, CA
Posts: 215
Thanks for all of the advice guys. I haven't pulled out the scope yet but have some good news. I did the "color afc alignment" procedure which only requires a voltmeter and now I can get very weak color. The alignment settings were not really that far off, so I am not sure if I tweaked it just enough to get a weak color signal and there is still an issue somewhere.

There is only a color image at the counterclockwise end of the fine tuning of the channel. It is also pretty difficult to get the color and picture stable at the end of the range. I have had trouble getting the color bars to sync properly as well.

I have a portable color bar generator, see attachments.
Reply With Quote
  #18  
Old 02-16-2019, 02:05 AM
Jon F's Avatar
Jon F Jon F is offline
VideoKarma Member
 
Join Date: Dec 2013
Location: Cupertino, CA
Posts: 215
I was watching the TV today for a little bit, but out of nowhere something else happened.

The screen is now red, brightness control doesn't really do anything. HV is down to ~18kV. Cathode current on 6JE6 runs high after the TV warms up. My initial thoughts are a loose connection or cracked solder joint.
Attached Images
File Type: jpg Screen Shot 2019-02-15 at 11.05.06 PM.jpg (27.7 KB, 16 views)
Reply With Quote
  #19  
Old 02-16-2019, 10:43 AM
old_coot88 old_coot88 is online now
VideoKarma Member
 
Join Date: Sep 2009
Posts: 1,959
If you haven't already done so, re-flow the two ground stakes on the far right end of the chroma board. If one of those goes open, it kills the heaters on the 6GU7s. Their plates go high, and since the plates are DC-coupled to the CRT grids, beam current goes out the roof, dragging the HV down. Also 6JE6 cathode current goes high.

This may not be what's causing your problem, but always reflow those stakes anyway. It's an endemic problem to CTC-12, '15, '16, '17, and '25.
Reply With Quote
  #20  
Old 02-16-2019, 03:29 PM
Jon F's Avatar
Jon F Jon F is offline
VideoKarma Member
 
Join Date: Dec 2013
Location: Cupertino, CA
Posts: 215
Quote:
Originally Posted by old_coot88 View Post
re-flow the two ground stakes on the far right end of the chroma board.
Thanks for the tip, I have reflowed these points. Powered up the TV this morning and still has the same issue.
Reply With Quote
Audiokarma
  #21  
Old 02-16-2019, 05:41 PM
Tom9589 Tom9589 is offline
VideoKarma Member
 
Join Date: Jan 2013
Posts: 178
Even though you have re-flowed these points, check the 6GU7s while the set is turned on to see if their filaments are lighting up.
Reply With Quote
  #22  
Old 02-16-2019, 06:39 PM
Jon F's Avatar
Jon F Jon F is offline
VideoKarma Member
 
Join Date: Dec 2013
Location: Cupertino, CA
Posts: 215
The filaments do light up
Reply With Quote
  #23  
Old 02-16-2019, 07:01 PM
Jon F's Avatar
Jon F Jon F is offline
VideoKarma Member
 
Join Date: Dec 2013
Location: Cupertino, CA
Posts: 215
Well I just reseated a bunch of tubes and now the problem is gone. I can’t seem to replicate it unfortunately.
Reply With Quote
  #24  
Old 02-16-2019, 09:13 PM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 6,548
Quote:
Originally Posted by Jon F View Post
Well I just reseated a bunch of tubes and now the problem is gone. I can’t seem to replicate it unfortunately.
One of the things I found was a connecting wire that was located around the area in question. It seemed to be affected by the heat of the tubes and the larger resistors. It seemed to arc and destroyed the 620mh peaking coils.
The first thing I did was remove it and relocate it under the PC board.
Reply With Quote
  #25  
Old 02-17-2019, 02:39 AM
Jon F's Avatar
Jon F Jon F is offline
VideoKarma Member
 
Join Date: Dec 2013
Location: Cupertino, CA
Posts: 215
Quote:
Originally Posted by dieseljeep View Post
One of the things I found was a connecting wire that was located around the area in question. It seemed to be affected by the heat of the tubes and the larger resistors. It seemed to arc and destroyed the 620mh peaking coils.
The first thing I did was remove it and relocate it under the PC board.
Is the circled wire in the attachment the one that gave you trouble?

I have also attached a couple more pictures of the set issues in operation. Most of the time when I can get color it doesn't lock in, more of a rainbow. Playing with the horizontal hold or fine tuning sometimes gets the chroma to sync properly.

I have done an experiment where I pull the chroma oscillator tube out during operation, let the tube cool down, and then put it back while the set is on. While the tube is warming up there is a point for a few second where the chroma locks in. However, after the tube is fully warmed up it becomes a rainbow again.

Also, having a little bit of trouble with horizontal sync in general as the vertical lines in the cross hatch are difficult to adjust to be straight.
Reply With Quote
Audiokarma
  #26  
Old 02-17-2019, 10:44 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 10,405
If the chroma osc has a broad lock in adjustment range I typically connect a color bar generator and with the color maxed adjust the fine tuning till the color is barely there (and hold the color osc in sync). The lock point should be smaller but still exist. Then I rock the channel selector and see if it holds sync, and tweak it so that it locks as fast as it can between channels with minimal color signal...If it will lock under those conditions normal viewing signal levels and finetuning position will be a piece of cake for it to lock to.

If it can only lock to strong color there are probably circuit issues or bad alignment problems.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #27  
Old 02-17-2019, 11:02 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 6,548
Quote:
Originally Posted by Jon F View Post
Is the circled wire in the attachment the one that gave you trouble?

I have also attached a couple more pictures of the set issues in operation. Most of the time when I can get color it doesn't lock in, more of a rainbow. Playing with the horizontal hold or fine tuning sometimes gets the chroma to sync properly.

I have done an experiment where I pull the chroma oscillator tube out during operation, let the tube cool down, and then put it back while the set is on. While the tube is warming up there is a point for a few second where the chroma locks in. However, after the tube is fully warmed up it becomes a rainbow again.

Also, having a little bit of trouble with horizontal sync in general as the vertical lines in the cross hatch are difficult to adjust to be straight.
That's the one. I see the other that gives trouble has already been replaced. Also the peaking coil has been jumpered out. Try to replace it if possible.
Reply With Quote
  #28  
Old 02-17-2019, 11:10 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: 4,837
Regarding the horizontal wiggles, two things could contribute:
1) Your color bar generator probably has a simple vertical sync pulse with no serrations; that interrupts the horizontal sync. This causes the horizontal AFC detector to output an erroneous voltage during V sync; then it has to recover.
2) The R and/or C values in the horizontal AFC filter circuit (between the detector and the oscillator) are off, causing an undamped, ringing response.

A possible third minor contribution could come from the sync separator itself, which is shown by the slight wiggle on every row. This may be normal for this set with this bar generator. I have seen it often on sets that otherwise operate fine with a standard video program source. It could also be affected by fine tuning.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #29  
Old 02-17-2019, 12:10 PM
Tom9589 Tom9589 is offline
VideoKarma Member
 
Join Date: Jan 2013
Posts: 178
Both of my dot-bar generators exhibit the same behavior.
Reply With Quote
  #30  
Old 02-17-2019, 03:19 PM
oldtvman's Avatar
oldtvman oldtvman is offline
Larry Melton (oldtvman)
 
Join Date: Jan 2005
Location: Mishawaka, Indiana
Posts: 726
Quote:
Originally Posted by Jon F View Post
I copy-pasted the 148V from pin 3, pin 6 should have read 268V. I updated the image below.


I have a scope, but do not use it much so my skills in diagnosing a TV with it are limited. Any tips on waveforms I should check?
If you have the schematic and it appears you do, it should show waveforms for different points of the set. I know Sams has waveform pictures based on using a color bar generator.
__________________
[IMG]
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 11:07 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.