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 08-10-2012, 07:24 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
I would say some resistance checks of the video out tube would be a good start, need to that plate voltage up (even though that would cut it off even harder, but start there.

Oh are are you reading the red K of the CRT? should be +320, just in case you read one of the other K and did not have the drive G1 drive fully advanced.
Reply With Quote
  #17  
Old 08-10-2012, 09:17 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
check the plate of the AGC keyer tube, look for the 600v PP spike on a scope.
Reply With Quote
  #18  
Old 08-13-2012, 08:15 AM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 290
The chassis is out of the cabinet in stand-alone. The HV is of course reduced (no DY attached) as is the pulse from the purple wire winding so the AGC plate pulse is low for now but still at 300 V peak and the blanker is low at the grid at -34volts. There are a number of resistors that have been replaced by me due to out of tolerance by a moderate amount. Plate resistors on the GU7s are out as well and still need replacement. Should be 27k and presently measure 21 / 22K and the tubes run hot. Focus volts is in the ballpark. Still the only video to be seen is at the left 1 inch or so of the screen and that's not very bright considering the screen volts and a good CRT with HV. Still plugging away.
Reply With Quote
  #19  
Old 08-13-2012, 06:42 PM
mstaton's Avatar
mstaton mstaton is offline
"Book em Dano!"
 
Join Date: May 2011
Location: Caldwell, Id
Posts: 1,600
I had a set that did a similar thing. If I turned the contrast one direction it looked like this(see thread: http://www.videokarma.org/showthread.php?t=252862) but id I turned it the other way, I got a weak but full raster. ALL the canned electrolytics were dry. Good HV and B+, screen volts OK.
__________________
"It's a mad mad mad mad world" !!
http://www.youtube.com/user/mwstaton64?feature=mhee
Reply With Quote
  #20  
Old 08-14-2012, 12:53 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 290
The quad E-can at the end has been replaced (bad seal, dripped, dried out) others are OK. I have subbed to make sure any way. Replaced the .1 on the agc line to the IF strip and the video from the detector looks more stable on the scope. Looks good going into the 12BY7, bad coming out I may just shotgun all the related components and reflow all the joints. I hate black magic fixes like that, I would prefer to know what exactly the fault is, but this is getting time consuming for this one problem alone and I have not yet seen what other things will have to be addressed.
Reply With Quote
Audiokarma
  #21  
Old 08-14-2012, 01:10 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
screen resistor/contrast pot/service switch for trouble with the Video out.

I have also replaced the grid coupling cap on the video, but if you are good at the grid then that should not be a problem, unless is just a bit leaky. That "could" account for the low plate voltage. I know you did voltage checks but don't remember the results.

I am assuming the 50uf cap on the contrast control is not shorted.

Last edited by DaveWM; 08-14-2012 at 01:14 PM.
Reply With Quote
  #22  
Old 08-14-2012, 07:01 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 290
Gonna go Oh Yea when ya hear this one.

Brief raster on the left dark screen with close focus. Drum roll please


The focus rectifier! Likely shorted. After seeing decent signal on the scope (after soldering all the parts in the area and grounds I still had the strange symptom yet wave forms and DC on the CRT grids and cathode looked good. The last thing to ponder "the focus grid. The voltage was a bit rich in AC content so a rectifier change was in order. I also discovered the previous person had a 100 ohm resistor in place of the 1 meg in series with the focus lead also.

I now have a picture in near focus but a unresponsive focus control. I can now view a picture and see there is much to do like AGC and sync issues. Vertical gain next, then color. The CRT is looking decent but the cap is scary loose and I've had to re-flow the solder in some of the pins.

Any suggestions to secure the base to keep it from moving short of JB weld? I don't want wires to break from movement

Progress is being made
Reply With Quote
  #23  
Old 08-14-2012, 07:30 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
if there is still some of the brown glue left but just not stuck, I have had luck with a product called "flex zap" you can get it at model shops. Its a kind of CA glue but has some give to it so as not to shock break in heat cycles.

If the focus is not responding, 1st check the focus voltage and make sure you are getting an adjustment of at least 500v. I use a simpson 260 in the 5kv mode.

does the focus coil look cooked?
Reply With Quote
  #24  
Old 08-14-2012, 09:00 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 290
Focus coil looks OK. I am going to check the value of the HV cap between the coil and the stick. I have run across a number of creative part subs so far.

As far as the CRT base cap goes I want secure it against mechanical movement but would like to have the option of getting behind it in the future if a last ditch (desperate) effort is needed by somebody. My concern is that even slight movement over a long period of time will lead to wires breaking off at the nibs. Present servicing and restoration just adds to the problem as the chassis is reconnected for testing and repair at present.
Reply With Quote
  #25  
Old 08-16-2012, 02:19 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
I think the flex zap will fill the bill. Never tried to break the bond after using it, but I suspect it would not take a lot.

when you were having the dark CRT before, I thought you said you had checked the focus voltage?

I have not seen a bad 130pf but that does not mean much as I have not been doing this long. Did you get a chance to see if the focus voltage varies at all with the coil? If not I would think one of the coils may be open. the way I understand how it works is sorta like an adjustable bucking transformer, two coils out of phase, the core simply moves from the out of phase to the in phase thereby adding or subtracting to the pulse from the fly that is then rectified by the stick. the 66meg is a load and the cap a filter.

Last edited by DaveWM; 08-16-2012 at 05:24 PM.
Reply With Quote
Audiokarma
  #26  
Old 08-16-2012, 09:30 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 290
I used an old meter and it showed just over 5kv but I suspect what it didnt show was the high AC content. Moving forward.
Reply With Quote
  #27  
Old 08-26-2012, 07:40 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 290
Pogress, but small vertical sweep.

Finally have a watchable picture but still a ways to go. My latest focus problem was a 100k resistor across the focus coil cooked its way down to 1700 ohms! I also found missing resistors in the horizontal osc stage. The most pressing issue for now is the vertical sweep. All vertical caps have been replaced except the cathode electrolytic. The tube has been swapped with no improvement. A couple out of tolerance resistors replaced as well. Can someone tell me what the deal is with the VDR? They never went bad in the old days but time could create a new scenario after 45years. The controls work, just not enough vertical gain.

I did find a bonding agent for the CRT base called Loctite GO2 from home depot. It seems to grab onto anything and when cured it has the feel of silicone with very little flex. It cures clear. The package indicates it should take the heat...Time will tell. The CRT was showing signs of being intermittent so I re-flowed all the pins secured the base after seeing stability return. The emission is good on all guns

This restore has not been fun at all due to the previous attempt to fix it. There have been poor choices in part substitution, values changed in an attempt to "make it work". Added to that this set shows signs of very high hours manifested as heat damage to terminal strips, heat blasted wire, and this chassis wins the Most Number of Out of Tolerance Resistors award of any restore or repair I have done.

End of rant
Reply With Quote
  #28  
Old 08-26-2012, 08:14 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
1st thing to confirm is that electro, if its open the vert will deflection will suffer.

next are you testing it with the convergence board plugged in?

I would not worry about the VDR, but if everthing else check out you can remove it and test. I use a cap tester to apply a voltage to it, and check the current thru it. IIRC its about 1ma at 800v. I doubt its a problem unless its shorted.
Reply With Quote
  #29  
Old 08-26-2012, 08:20 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
also check the boost voltage and look for some high value resistors that supply the boost voltage to on of the pots (I cant recall if RCA calls it the height or lin pot, but one of them will have boost voltage on one side and B+ on the other).

I think there its a 2.2 meg or some other high value resistor that if it drifts up will hurt deflection.
Reply With Quote
  #30  
Old 08-27-2012, 12:41 PM
holmesuser01's Avatar
holmesuser01 holmesuser01 is offline
VideoKarma Member
 
Join Date: Jul 2005
Location: Asheville NC
Posts: 1,731
Quote:
Originally Posted by DaveWM View Post
also check the boost voltage and look for some high value resistors that supply the boost voltage to on of the pots (I cant recall if RCA calls it the height or lin pot, but one of them will have boost voltage on one side and B+ on the other).

I think there its a 2.2 meg or some other high value resistor that if it drifts up will hurt deflection.
I got zapped but good once by a vertical centering pot on one of my many RCA sets. I think it had B+ on it.
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 06:04 PM.



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