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
  #46  
Old 04-21-2018, 10:21 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,109
Quote:
Originally Posted by old_tv_nut View Post
I didn't understand what it was you disconnected in that video. I did intend for you to disconnect the antenna input, not the IF.

Anyway, I think the next thing I would try (after disconnecting and reconnecting the antenna) is removing/swapping the RF amplifier (V1).
Yeah, I disconnected the ant lead to the 75/300 ohm adapter.
I swapped all 3 tubes in the tuner (6J6) with a good one from stock. Still no joy. I also subbed out the 6AU6 DC Restorer tube and that didn't help either.
Reply With Quote
  #47  
Old 04-23-2018, 11:34 PM
Penthode's Avatar
Penthode Penthode is offline
VideoKarma Member
 
Join Date: Jun 2009
Location: Syracuse, NY
Posts: 664
If the mica caps have been changed in the IF strip, the IF strip most certainly requires a proper sweep alignment. It looks like the alignment is truly and well out.

Proper alignment is not too huge a task. It just require a bit of knowledge, some patience and the pro power equipment. I learned to sweep align a TV if strip as a teenager more than 50 years ago and the knowledge once gained will remain useful.
Reply With Quote
  #48  
Old 04-27-2018, 10:56 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,109
I have a BK 1077B and injected video on the grid of the Video amp. Worked well. Then used the IF mode to inject a signal from each of the 4 IF stages. Same problem.
I'm suspecting the Video Detector circuits. It is a 6AL5. Is there anyway to use the 1077B to check this section out? The manual and Kiver's book seem to skip over this section of circuitry. BTW I substituted the tube with a another one that checked good. No joy.
Reply With Quote
  #49  
Old 04-27-2018, 11:10 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: 4,557
You should be able to inject your IF signal directly into pin 1 of the PIX 2nd detector and see something if it's strong enough to drive that point.

When injecting into the grid of each IF stage, did you pull the preceding stages' IF tubes (to make sure they are not driving some garbage in with your injected signal)?

Edit: have you checked for open coils in the detector circuit?
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany

Last edited by old_tv_nut; 04-27-2018 at 11:15 PM.
Reply With Quote
  #50  
Old 04-28-2018, 07:46 PM
Username1's Avatar
Username1 Username1 is offline
Not sure how I got here.
 
Join Date: Dec 2009
Location: Orange County NY
Posts: 3,470
Silly me, but it sounds like the sound is good and clear..... Not the IF ???

Looks like the streaking may be the set trying to sync off any dark spot
in the picture..... You will recognize this if you ever played with over the
air scrambled pay tv.....

What's going on around the video detector circuit....

Not sure where all that stuff gets picked off on a 630.....

Good long video by the way... Hard to get anything off the ones
people post that are only 20 - 30 seconds long.....


.
__________________
Yes you can call me "Squirrel boy"
Reply With Quote
Audiokarma
  #51  
Old 04-28-2018, 09:12 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,109
I found the problem. It was one of the Peaking coils from the Dectector stage.

Item # L188 in the RCA manual and #L119 in Sams 54-18. This Peaking coil came form the junction of another Peaking coil from the plate (pin 7) of the 6AL5 Dector and the Coupling cap #c138 (.05uf) RCA, and C50 in the Sams manual. From the junction is the bad Peaking coil, then it goes to a 3900 ohm resistor to ground.

I couldn't not fix it. I had one end, but could not locate the other. I looked up the properties (8 ohms and 250muh) and looked up a similar coil in a spare parts Motorola chassis that I have. Sure enough there was one that was 7.2 ohms and it was a "Yellow Dot" coil. I found it and clipped it out and soldered it in. Bingo!

The picture isn't all that good but it does confirm the bad coil was the problem.

Thank to all you offered help. old -tv-nut got to thinking I need to recheck those coils. That was the key.
I'm locating a replacement coil from a parts chassis that my buddy has so when I get that soldered in. I'll do a quick alignment, and declare this off my bench.

I could have sworn I checked all those coils before! Sigh......


Reply With Quote
  #52  
Old 04-29-2018, 02:31 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: 4,557
hooray!

The coils in the detector circuit are not for peaking, but for suppressing the IF frequencies and harmonics. They must have continuity to pass the detected video to the first video amp. I think what you see with the coil open is a weird DC clamping effect involving the first video amp grid.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #53  
Old 04-29-2018, 03:25 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: 4,557
Oops - I read it wrong - L188 is a peaking coil.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #54  
Old 05-01-2018, 06:10 PM
pdr-fml pdr-fml is offline
VideoKarma Member
 
Join Date: Oct 2016
Posts: 23
peaking coil

Quote:
Originally Posted by old_tv_nut View Post
hooray!

The coils in the detector circuit are not for peaking, but for suppressing the IF frequencies and harmonics. They must have continuity to pass the detected video to the first video amp. I think what you see with the coil open is a weird DC clamping effect involving the first video amp grid.
Being pretty new to this I have heard about peaking coils going bad and I was wondering what is usually the cause of failure? Is it always a open coil or does the resistor ever go open or change value. And what causes them to go open -excessive current -physical damage?
Reply With Quote
  #55  
Old 05-01-2018, 06:38 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: 4,557
The resistor in parallel (if the peaking coil has one) affects the bandwidth of the peak (or null, if it is used in a trap circuit). The DC resistance of the coil is usually much lower than the parallel resistor, so the resistor value could change a lot and you might not notice the effect. Coil failure hypothetically can be either opening, or shorting of one turn to another.

I think that these low power peaking coils usually fail open due to corrosion over a long period. Coils and transformers that carry high power (like in the deflection circuits) can fail due to heat or arcs causing shorted windings. In this case, the AC operation is ruined, but the DC resistance may not change much, because only one turn is shorted out of tens or hundreds.

Maybe some others can chime in on which types of failures typically occur in different coil applications.
__________________
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 12:35 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.