Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Vintage TV & Radio Tech Forum

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 02-15-2013, 08:36 AM
vts1134's Avatar
vts1134 vts1134 is offline
Looking For Time
 
Join Date: Apr 2011
Location: Pittsburgh, PA
Posts: 1,532
Not Quite Sure What To Call This

I'm not sure what term to use when describing the problem in the picture below. Any time there is a white to black image, the white will "bleed over". Smearing? In any case the picture below was the best (worst) image I could find to produce this problem. Can any one tell me what this problem is called, and what the possible causes of this problem might be?

Reply With Quote
  #2  
Old 02-15-2013, 10:55 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
Nobody have an idea? I have to say I can't guess why.

Also hard to see exactly what the symtpom is ...Hard to tell if the white bleed is actually starting AFTER the first line of white letters and continuing onto following lines, or is across the whole first line as well as every line.

Can you do anything to the controls that changes it? If so, that might lead you to the section causing trouble. Other than that, no clue. Any change with fine tuning?

If you have spare tubes, I'd try changing IF, video amp, AGC, sync separator.

What set is this?
Reply With Quote
  #3  
Old 02-16-2013, 07:33 AM
vts1134's Avatar
vts1134 vts1134 is offline
Looking For Time
 
Join Date: Apr 2011
Location: Pittsburgh, PA
Posts: 1,532
Quote:
Originally Posted by old_tv_nut View Post
Nobody have an idea? I have to say I can't guess why.

Also hard to see exactly what the symtpom is ...Hard to tell if the white bleed is actually starting AFTER the first line of white letters and continuing onto following lines, or is across the whole first line as well as every line.
The symptom is on every line. I turned the brightness up a bit to accentuate the problem for this picture. When you are watching a normal scene the problem doesn't look this bad, but it is definitely there. White text on black background is the easiest way to show the problem.

Quote:
Originally Posted by old_tv_nut View Post
Can you do anything to the controls that changes it? If so, that might lead you to the section causing trouble.
The symptom doesn't change with any control setting. It becomes more visible as the brightness is turned up, but the ratio of brightness of the symptom to the text doesn't change.

Quote:
Originally Posted by old_tv_nut View Post
If you have spare tubes, I'd try changing IF, video amp, AGC, sync separator.

What set is this?
I'm almost positive that it isn't the IF. The picture above is using the entire set with an RF modulated DVD player, but I can bypass the IF stage completely with my B&K television analyst and the problem is still present. Unless the B&K is somehow causing the same problem in an unrelated way, it must be forward of the video detector.
There is no AGC in the set btw.

Quote:
Originally Posted by old_tv_nut View Post
What set is this?
This set is my 630ts. I don't know if it is apropos to this problem but the contrast control on this set seems more like an on/off switch. There is only three different settings- no video- weak contrast- good contrast. Other sets that I have are more of a gradual even ramping of the contrast level from no video to over driven. I've begun checking the resistors around that area and all are good so far.
Reply With Quote
  #4  
Old 02-16-2013, 08:33 AM
Geist Geist is offline
VideoKarma Member
 
Join Date: Dec 2012
Posts: 350
Hi All;
I would say check the Video section.. The video amp is not flat in its amplification of the video signal.. It remind me of a too narrow bandwidth.. But, it could be the IF section if it is not wide enough to carry the full bandwidth..
Thank You Marty
Reply With Quote
  #5  
Old 02-16-2013, 09:03 AM
Geist Geist is offline
VideoKarma Member
 
Join Date: Dec 2012
Posts: 350
Hi all;
In my other book with pictures,, it says possible causes for trouble..
Contrast control set too high, overloading the the amplifiers..
Video IF amplifier wongly aligned, with the video IF Carrier too low on the side of the response curve..
Faults in the Video Detector and / or Video Amplifier circuits.. Check coupling capacitors, decoupling capicators and bypass capicators for open circuits.. Check Plate Load resistors and grid resistors for incorrect values or shorting.. Amplifier grid biases may be insufficiently negative allowing grid current to flow..
Those with more experience, might be able to elaborate..
THANK YOU Marty

Last edited by Geist; 02-16-2013 at 09:20 AM.
Reply With Quote
Audiokarma
  #6  
Old 02-16-2013, 10:33 AM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
would be interesting to see if you could see it on a scope. Need a fixed image of course and then look at each line of data (horz scan rate) compare the composite video to the output of the detector,then trace thru to the CRT grids (or cathode if that is how it goes).

Did you try a composite video injection at the video amp grid (sorry if you mentioned it already)?

Maybe just a weak CRT that the cutoff is not that sharp.
Reply With Quote
  #7  
Old 02-16-2013, 11:41 AM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Quote:
Originally Posted by vts1134 View Post
...I'm almost positive that it isn't the IF.
That's a correct assessment. The absence of any appreciable ringing or smearing-out of fine detail in the pic would rule out misalignment of the IFs.
The problem is almost certainly in the video chain. Have you checked the peaking coils for continuity? Looks to be eight of 'em sprinkled from the detector and the CRT.
If they're all good, injecting with your B&K point by point thru the video chain (attenuating as necessary) oughta spot the problem.
Quote:
I don't know if it is apropos to this problem but the contrast control on this set seems more like an on/off switch. There is only three different settings- no video- weak contrast- good contrast. Other sets that I have are more of a gradual even ramping of the contrast level from no video to over driven.
That sounds almost like the control is cruddy/scratchy. If you have an analog ohmeter, check to see if it runs smoothly from stop to stop without drop-outs or jumpiness.
Reply With Quote
  #8  
Old 02-16-2013, 01:02 PM
vts1134's Avatar
vts1134 vts1134 is offline
Looking For Time
 
Join Date: Apr 2011
Location: Pittsburgh, PA
Posts: 1,532
Quote:
Originally Posted by DaveWM View Post
Maybe just a weak CRT that the cutoff is not that sharp.
I have another 10BP4 that doesn't give me as good a picture as this one. It displays the symptom as well.



Quote:
Originally Posted by DaveWM View Post
would be interesting to see if you could see it on a scope. Need a fixed image of course and then look at each line of data (horz scan rate) compare the composite video to the output of the detector,then trace thru to the CRT grids (or cathode if that is how it goes).
I'll give this a shot, but I am still extremely green with scope interpretation.

Quote:
Originally Posted by old_coot88 View Post
The problem is almost certainly in the video chain. Have you checked the peaking coils for continuity? Looks to be eight of 'em sprinkled from the detector and the CRT.
If they're all good, injecting with your B&K point by point thru the video chain (attenuating as necessary) oughta spot the problem.
The coils are all good.
Unfortunately I don't 100% trust my B&K at the moment. I think it needs some servicing of it's own for a few reasons. It's quite a shame as this is precisely what it is good for. That will be my next project on the bench.

Quote:
Originally Posted by old_coot88 View Post
That sounds almost like the control is cruddy/scratchy. If you have an analog ohmeter, check to see if it runs smoothly from stop to stop without drop-outs or jumpiness.
That 's what I thought also, but it ramps smooth as silk from 0 to 10k.

I think I'm going to go resistor hunting in my video section and see what I can find.
Reply With Quote
  #9  
Old 02-16-2013, 01:20 PM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
VideoKarma Member
 
Join Date: Jan 2006
Posts: 4,030
The Picture control on a 630TS is confusingly named. It is a manual gain control and its effect is not like a contrast control on newer TVs.

The Picture control varies the gain (i.e., amount of amplification) on the overall signal. You may find that it has a pretty narrow range where the picture & sound are acceptable. You may also need to readjust the Picture control when changing to a different source with a weaker or stronger signal.

To some extent, what you're experiencing is normal for a 630TS. At one end of that control's range you'll get almost no signal, and at the other end you'll get wackadoodle picture & sound.

Bear in mind that 1940s TVs were designed to be watched in dim lighting. I suspect we're all guilty from time to time of cranking the controls up too high and expecting these old sets to have an ultra-bright screen like modern TVs, that you can watch in a sunlit room.

There was a recent thread in another forum by a guy who had similar horizontal lines (on a different television) that looked like overdriven video. I think they disappeared when he removed (or changed?) a modification he had installed to minimize retrace lines.

On a general note, if you go treasure hunting to check resistors, check mica caps, too. Micas used to be thought immortal, but now more and more of them are found faulty. When I redid my 630TS 1,000 years ago, an oldtimer told me to replace the mica coupling caps in the video IF chain.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Last edited by Phil Nelson; 02-16-2013 at 02:21 PM.
Reply With Quote
  #10  
Old 02-16-2013, 02:21 PM
ChrisW6ATV's Avatar
ChrisW6ATV ChrisW6ATV is offline
Another CT-100 lives!
 
Join Date: Feb 2007
Location: Hayward, Cal. USA
Posts: 3,464
If this was a solid-state TV, I would say it has bad electrolytic capacitors in the video circuits. Double-check the values of the capacitors replaced in those circuits.
__________________
Chris

Quote from another forum: "(Antique TV collecting) always seemed to me to be a fringe hobby that only weirdos did."
Reply With Quote
Audiokarma
  #11  
Old 02-16-2013, 04:20 PM
vts1134's Avatar
vts1134 vts1134 is offline
Looking For Time
 
Join Date: Apr 2011
Location: Pittsburgh, PA
Posts: 1,532
Quote:
Originally Posted by Phil Nelson View Post
At one end of that control's range you'll get almost no signal, and at the other end you'll get wackadoodle picture & sound.
That's exactly what I was expecting with the control, but at one end I get 0 signal, when I turn it up at one point I get low signal followed immediately with normal signal. What I can't get is the wackadoodle picture no matter how high I crank the control.

Quote:
Originally Posted by Phil Nelson View Post
Bear in mind that 1940s TVs were designed to be watched in dim lighting. I suspect we're all guilty from time to time of cranking the controls up too high and expecting these old sets to have an ultra-bright screen like modern TVs, that you can watch in a sunlit room.
I will admit that I am guilty of that from time to time. When I set the brightness control at it's proper value for viewing in a dimly lit room, and the source is full motion video, the problem is almost unnoticeable. Almost unnoticeable doesn't mean the problem doesn't exist though. It needs to be found and repaired.
Reply With Quote
  #12  
Old 02-16-2013, 05:35 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Phil,
Did your 630ts exhibit any sign of those full width 'ribbon lines' that Vts1134 is chasing? Sometimes ya gotta wonder if certain quirks in the old sets aren't just the nature of the beast (like the horz nonlinearity in your T-100, wherein i had the identical problem in a T-100 many years ago and never could run it down).

Last edited by old_coot88; 02-16-2013 at 05:42 PM.
Reply With Quote
  #13  
Old 02-16-2013, 06:39 PM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
VideoKarma Member
 
Join Date: Jan 2006
Posts: 4,030
I honestly don't recall if my 630TS showed those lines, although I know I have seen similar lines in some old TV or another during the last several years. Maybe tomorrow I can fire up the 630 and look at some images. It's in a location where it looks pretty but rarely gets played.

The content that we watch today has lots of lettering with extreme contrasts --static title screens, screens with text crawl at the top and bottom, etc. -- which brings out the worst in some old TVs.

Phil Nelson
Reply With Quote
  #14  
Old 02-16-2013, 07:45 PM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
VideoKarma Member
 
Join Date: Jan 2006
Posts: 4,030
I was too curious to wait, so I played my 630TS and it doesn't show those lines, even on static title screens with extreme contrast.

Turning the Picture control from one extreme to the other gives you no signal at the CCW end of the range, and then if you turn it up (CW) too far, the picture distorts and eventually loses sync.

The tuner has gotten a little flaky, no doubt from sitting around without being played. I really need to go around and exercise all of my restored sets more often.

Phil Nelson
Reply With Quote
  #15  
Old 02-16-2013, 08:59 PM
vts1134's Avatar
vts1134 vts1134 is offline
Looking For Time
 
Join Date: Apr 2011
Location: Pittsburgh, PA
Posts: 1,532
Thanks for looking Phil. I wouldn't describe this as full width ribbon lines in the picture. The trailing white only happens to the right if the brightness control is set to a normal level. It's like some one takes the right hand edge of a white object and pulls it out horizontally to the right.
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 12:42 PM.



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