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
  #16  
Old 02-11-2019, 11:14 PM
Jon1967us Jon1967us is offline
VideoKarma Member
 
Join Date: Nov 2018
Posts: 14
Quote:
Originally Posted by Electronic M View Post
Many PCB sets in the tube era were built with the intention that the PCB be serviced while still mounted to the chassis...Most offered some way to get at the foil side to solder, but some makes Like GE and Philco encouraged crushing the body of a failed original part, leaving the original leads as points to wrap/J-hook the replacement parts leads onto. I have service Lit for GE that literally recommends and instructs how to replace a part in that manner.
Funny you say that bc I considered doing the very same. I've been j hooking the ones where I can access the leads, but the radial ones with hidden leads proved daunting. I will give it a shot with some pliers.
Reply With Quote
  #17  
Old 02-12-2019, 09:39 AM
Notimetolooz's Avatar
Notimetolooz Notimetolooz is offline
VideoKarma Member
 
Join Date: Mar 2014
Location: Dallas, TX
Posts: 196
Quote:
Originally Posted by Jon1967us View Post
You mean the yoke cover? Very fancy. Does the cover serve any purpose other than a means of holding the yoke in place and acting as a sort of guide for the adjustment?
In his case the rear cover also held the centering rings (these are magnetic).
The yoke has to be kept stationary with respect to the CRT because any movement between them will effect the image centering, size and rotation.
Reply With Quote
  #18  
Old 02-14-2019, 11:21 AM
Jon1967us Jon1967us is offline
VideoKarma Member
 
Join Date: Nov 2018
Posts: 14
Quote:
Originally Posted by jr_tech View Post
“ no video at this point.”

Does the brightness control have normal range?

jr
Seems to have normal range
Reply With Quote
  #19  
Old 02-14-2019, 03:30 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 3,873
Good.

Out of curiosity, what signal source are you feeding to the tv when you get sound but no video?

jr
Reply With Quote
  #20  
Old Yesterday, 12:49 AM
Jon1967us Jon1967us is offline
VideoKarma Member
 
Join Date: Nov 2018
Posts: 14
Quote:
Originally Posted by Electronic M View Post
check your video detector diode and vid amp biases.
Well, it seems that the detector diode is hidden in the metal can as indicated by the left most arrow. I have no way of getting to it other than spending 4 hours disconnecting and desoldering everything to remove the board. This board is totally unserviceable.




Also, the Vid output tube has the test pins INSIDE the tube cover. No way to get to them with the tube in. The Mercury tube checker says the tube is fine by the way. Could I check the bias voltages with the tube out? Otherwise, there are barely visible traces by the socket. I may be able to check the voltages there.

Back to the detector diode, what are the chances it has failed? Do these old Ge Shottkeys have a reputation for failure?

Note, I am feeding a video signal in with a D>A converter box, connected to the antenna lugs.
Reply With Quote
Audiokarma
  #21  
Old Yesterday, 12:50 AM
Jon1967us Jon1967us is offline
VideoKarma Member
 
Join Date: Nov 2018
Posts: 14
Quote:
Originally Posted by jr_tech View Post
Good.

Out of curiosity, what signal source are you feeding to the tv when you get sound but no video?

jr
I am feeding a video signal in with a set top D>A converter box, connected to the antenna lugs.
Reply With Quote
  #22  
Old Yesterday, 12:51 AM
Jon1967us Jon1967us is offline
VideoKarma Member
 
Join Date: Nov 2018
Posts: 14
Quote:
Originally Posted by Notimetolooz View Post
In his case the rear cover also held the centering rings (these are magnetic).
The yoke has to be kept stationary with respect to the CRT because any movement between them will effect the image centering, size and rotation.
I will most likely secure these with large zip ties. Hopefully that will be sufficient.
Reply With Quote
  #23  
Old Yesterday, 09:38 AM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 10,376
Quote:
Originally Posted by Jon1967us View Post
Well, it seems that the detector diode is hidden in the metal can as indicated by the left most arrow. I have no way of getting to it other than spending 4 hours disconnecting and desoldering everything to remove the board. This board is totally unserviceable.




Also, the Vid output tube has the test pins INSIDE the tube cover. No way to get to them with the tube in. The Mercury tube checker says the tube is fine by the way. Could I check the bias voltages with the tube out? Otherwise, there are barely visible traces by the socket. I may be able to check the voltages there.

Back to the detector diode, what are the chances it has failed? Do these old Ge Shottkeys have a reputation for failure?

Note, I am feeding a video signal in with a D>A converter box, connected to the antenna lugs.
They make a tool for getting those voltages with the tube installed... called a socket extender or socket saver....they go between the scoket and tube, lift the tube an inch or two and have test points on top.

I'd reckon video detectors prior to the late 60s had a 30% failure rate... the older the worse.
Most weren't shottkeys but Crystal diodes....they predated the transistor in consumer electronics.
__________________
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
  #24  
Old Yesterday, 09:47 AM
WISCOJIM WISCOJIM is offline
VideoKarma Member
 
Join Date: Sep 2005
Location: Grand Chute, Wisconsin
Posts: 2,042
Quote:
Originally Posted by Electronic M View Post
They make a tool for getting those voltages with the tube installed... called a socket extender or socket saver....they go between the scoket and tube, lift the tube an inch or two and have test points on top.
Sample image. Many are available on ebay, get one that matches the number of tube pins you need.


Attached Images
File Type: jpg sa.jpg (96.6 KB, 20 views)
Reply With Quote
  #25  
Old Yesterday, 01:40 PM
Notimetolooz's Avatar
Notimetolooz Notimetolooz is offline
VideoKarma Member
 
Join Date: Mar 2014
Location: Dallas, TX
Posts: 196
I don't know exactly how your chassis is arranged, but sometimes getting to parts isn't easy, its just part of the task. When you have more restorations under your belt you get used to it and perhaps have a better eye for getting to things.
This article by Phil might give you some tips. Maybe in your case also it may make sense to remove the CRT to get to the detector diode.
https://www.antiqueradio.org/RCA_14-...Television.htm
Reply With Quote
Audiokarma
  #26  
Old Yesterday, 02:26 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 3,873
Since the sound IF signal is taken from the plate of the video output, and the sound is ok, wouldn’t that imply that the video chain up to that point (diode included) is functioning ok?

jr
Reply With Quote
  #27  
Old Yesterday, 04:26 PM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 10,376
Quote:
Originally Posted by jr_tech View Post
Since the sound IF signal is taken from the plate of the video output, and the sound is ok, wouldn’t that imply that the video chain up to that point (diode included) is functioning ok?

jr
The diode rectifies the AM carrier to make video and passes the FM carrier for sound....if the diode shorts it won't make video for the video amp but the sound will still flow down the chain normally....heck if the diode opens and passes just enough signal through capacitive coupling to the video amp you could still get sound.... video detector fails are fun.

If you.can inject and watch video on the vid amp side of the diode then you know the diode failed.
__________________
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
  #28  
Old Yesterday, 06:31 PM
Jon1967us Jon1967us is offline
VideoKarma Member
 
Join Date: Nov 2018
Posts: 14
Quote:
Originally Posted by Electronic M View Post
The diode rectifies the AM carrier to make video and passes the FM carrier for sound....if the diode shorts it won't make video for the video amp but the sound will still flow down the chain normally....heck if the diode opens and passes just enough signal through capacitive coupling to the video amp you could still get sound.... video detector fails are fun.

If you.can inject and watch video on the vid amp side of the diode then you know the diode failed.
Should be easy to test the diode under normal conditions, except that it's near impossible to get to. I can't really get behind the board to unsolder the can. Really thinking of a brute force way of getting to it, IE a Dremel or something Would like to avoid spending upwards of 4+ hours unsoldering everything needed to free this board and then resoldering everything...but given the long weekend I just may have to bit the bullet.

I have plenty of germanium diodes on hand.

By injecting the video signal, could I plausibly take the yellow video out from the D to A converter output? would that be the right method? I've never done it before.

I'm aware of the Tube socket adapters. The problem here is that there is a metal cover, so one would need to pry that off to fit an adapter in.
Reply With Quote
  #29  
Old Yesterday, 07:31 PM
Jon1967us Jon1967us is offline
VideoKarma Member
 
Join Date: Nov 2018
Posts: 14
Quote:
Originally Posted by WISCOJIM View Post
Sample image. Many are available on ebay, get one that matches the number of tube pins you need.


OK, I didn't see the image when I first saw the post. I believe this configuration should work as it appears tall enough to clear the metal shield. I'll look out for one.
Reply With Quote
  #30  
Old Yesterday, 07:41 PM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 10,376
Quote:
Originally Posted by Jon1967us View Post
Should be easy to test the diode under normal conditions, except that it's near impossible to get to. I can't really get behind the board to unsolder the can. Really thinking of a brute force way of getting to it, IE a Dremel or something Would like to avoid spending upwards of 4+ hours unsoldering everything needed to free this board and then resoldering everything...but given the long weekend I just may have to bit the bullet.

I have plenty of germanium diodes on hand.

By injecting the video signal, could I plausibly take the yellow video out from the D to A converter output? would that be the right method? I've never done it before.

I'm aware of the Tube socket adapters. The problem here is that there is a metal cover, so one would need to pry that off to fit an adapter in.
So there are no holes in the metal under the PCB to access the traces? I'm not familiar with that model, but many sets (even some members of the much maligned Philco Predicta family) have some holes under the board where with a really thin iron and the correct angle you can access most of the solder pads.

On sets where you can't get at the pads you need, if you are strategic on which wires you unsolder you can hinge a side of the board up something like 30 degrees to access all the pads by only disconnecting a small fraction of the wires.
Shielding is important in operation...If you damage the can you will come to regret it.

Test adapters are typically the same diameter as the thinnest tube that plugs into the socket so as long as it is taller than the shield there should be no problem using it...Techs needed their adapters to work ANYPLACE the tube would so if a company made one that didn't they'd get some harsh comeuppance from their customers. One thing you can do if you need an adapter fast and have a spare socket of the right type and a dud tube that fits it, is make your own adapter...Carefully bust all glass but the base, cut all leads inside the dead tube as far from the base as feasible and solder wires (3" is probably a good length) from them to the socket keeping the lead order correct.
A lazier way if you have several good spare tubes of the right type that you don't mind killing is to solder thin wires to the top of the pins for test points...If you heat too long the glass will crack and the tube will die of vacuum loss.

Video injection: With tube era test equipment like a B&K 1077 it is usually a matter of connect and done (the equipment has protection/isolation circuits in place to prevent damage).
With a modern signal source like a converter box plug and play can destroy your signal source unless you perform prior due diligence checks and use care.
First check: is your sets B+ and heater system powered through a transformer? If not you need an AC line isolation transformer to power the TV (and only the TV) thru before you can safely proceed.
Next (regardless of the results of the first check): is there a sizable AC or DC voltage between your sets signal ground and your converter boxes ground jack...If yes stop and get a TV service video generator or use a converter box that you don't mind possibly killing.
Now you can connect the outer shield of the converter box yellow video cable to the signal ground. Then use a .1uF 600V capacitor in series between the center hot lead of the video cable and your injection point....The capacitor couples the video signal to the injection point and blocks any harmful DC that could exist on your intended injection point (or from any adjacent point you might accidentally touch the lead to).

Also, bear in mind a converter box has standard video level and video polarity, and some TV sets do not use both at once at any valid injection point...That may result in an inverted monochrome picture, weak or overdriven video, and or no deflection sync (the synch separator relies on the right polarity and a decent approximation of the right level of video to function).
A proper TV test pattern generator for servicing has a video output that is adjustable for both polarities and amplitudes far greater than a converter can produce.
If you encounter a set with 2 video amp tubes the grid of the first may have negative video and the plate of the first (and grid of the second) may have positive video while the plate of the second has negative video again...Or every polarity is opposite. The waveform leaving the plate of a tube is always inverted polarity from that entering the grid. The polartiy that comes out the video detector diode is determined by the (even or odd)number of IF stages (as well as the correct polarity installation direction of the diode). So the number of IF stages dictates whether you get composite video standard polarity (but not necessarily amplitude) at the detector or not.
__________________
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
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 01:08 PM.



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