Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Solid State CRT Televisions

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #16  
Old 01-11-2019, 11:36 AM
Jeff Jeff is offline
VideoKarma Member
 
Join Date: Oct 2015
Posts: 17
Quote:
Originally Posted by zeno View Post
You may try lifting pin 12 & see if you get 1-2V P-P of video on the
pin. You could also try hooking in composite video at TP 6 from a DVD. Just
be sure to use isolation !

73 Zeno
LFOD !
Just for good measure, I replaced the IF amp IC again, this one was a completely different brand and seller, and it does the same thing. Pulled pin 12 and there was just a flat line all the way down to the 100mv range. The thing is, when I inject a composite video signal straight to the video amp, It basically does the same thing with it's color situation, but I just assumed this was because composite is only 1v pp and the circuit expects 2v pp.
Reply With Quote
  #17  
Old 01-12-2019, 09:17 AM
kf4rca kf4rca is offline
VideoKarma Member
 
Join Date: Feb 2015
Posts: 268
You should have seen something. Its probably not a problem with the IF amp.
Hope you put a socket in there.
Lets back up. Do you have ALL your supply voltages?
__________________
Reply With Quote
  #18  
Old 01-12-2019, 06:58 PM
Jeff Jeff is offline
VideoKarma Member
 
Join Date: Oct 2015
Posts: 17
Quote:
Originally Posted by kf4rca View Post
You should have seen something. Its probably not a problem with the IF amp.
Hope you put a socket in there.
Lets back up. Do you have ALL your supply voltages?
140v rail is 142v, pin 3 (155v) is 159v, 22v rail is 24v, 12v rail is 12v, 35v rail is 36v, and I can't think of any others.
Reply With Quote
  #19  
Old 01-13-2019, 12:47 PM
kf4rca kf4rca is offline
VideoKarma Member
 
Join Date: Feb 2015
Posts: 268
Are you able to get sound thru to the speaker?
__________________
Reply With Quote
  #20  
Old 01-13-2019, 08:47 PM
Jeff Jeff is offline
VideoKarma Member
 
Join Date: Oct 2015
Posts: 17
Quote:
Originally Posted by kf4rca View Post
Are you able to get sound thru to the speaker?
Yes, very loud static when no station is tuned in, and with a signal tuned in, sound is fairly clear with normal volume.
Reply With Quote
Audiokarma
  #21  
Old 01-14-2019, 10:09 AM
kf4rca kf4rca is offline
VideoKarma Member
 
Join Date: Feb 2015
Posts: 268
Have you checked L126, L128, and L145 for continuity?
__________________
Reply With Quote
  #22  
Old 01-14-2019, 04:00 PM
Jeff Jeff is offline
VideoKarma Member
 
Join Date: Oct 2015
Posts: 17
Quote:
Originally Posted by kf4rca View Post
Have you checked L126, L128, and L145 for continuity?
L126, L128, and L145 all measure good continuity, but I do have some news. I've managed to source a working set with an AA chassis, and when I lift pin 12 of the IF amp IC and measure the waveform from pin 12, I get a 4v pp to 6v pp signal, but when I take the very same IC and put it in my set, (I've installed a socket in my set, though the AA's chassis is already socketed) I get a flat line out of pin 12 with it lifted.
Reply With Quote
  #23  
Old 01-15-2019, 12:05 PM
kf4rca kf4rca is offline
VideoKarma Member
 
Join Date: Feb 2015
Posts: 268
That's great

What I would do is put both chassis side by side (make sure everything is connected up) and do comparative ohm-meter checks (with the set off, of course).
I've been thinking you've got an open in the circuit traces some where. Maybe the set took a spill and you've got a hairline crack somewhere.
I've seen that before. Good luck.
__________________
Reply With Quote
  #24  
Old 01-17-2019, 07:21 PM
Jeff Jeff is offline
VideoKarma Member
 
Join Date: Oct 2015
Posts: 17
So I figured it out... Initially I was trying to figure out why I wasn't getting a signal out of pin 5 of the IF amp IC, so I tried some stuff not really worth mentioning... only to find out that pin 3 of the IC was shorted to ground. C140 in the schematic was responsible for the short, and once replaced I was able obtain a good signal out of pin 5. But, the set's picture still displayed the same issues as previously discussed. So, after some probing I found that I had a good signal out of Q200, but basically no signal out of Q205. I replaced Q205 with no change, checked it, and it checked just fine. I then found that R206 on the schematic, which comes out of the emitter of Q205 and goes through an inductor to ground, was practically open, and had a burn spot. Upon replacing it, the set now behaves like I think it should. So how did the resistor burn up? Well, a while back I was trying to directly inject a video signal into this set, which little did I know doesn't play well with a transformerless set. From what I understood, Q200 went POP when the grounded rca cable tip shot 120v through it, then through chassis ground, then through one of the bridge rectifiers (which also blew) to the hot side of the plug. So prior to posting here, I had replaced Q200, and R202, which was between it and chassis ground. What I didn't know was that it also blew R206, which was between Q205 and chassis ground.

TLDR: I blew it up and didn't replace everything that blew.
Reply With Quote
  #25  
Old Yesterday, 09:34 AM
kf4rca kf4rca is offline
VideoKarma Member
 
Join Date: Feb 2015
Posts: 268
Congratulations!

I think that set has a bridge rectifier power supply. So its ground is ground to that set only.
Those sets cannot have an external video input for that reason. Modern sets have a switching supply and the transformer in it provides the isolation for external grounded video inputs.
There are video transformers out there but they are kind of pricey ($22).
Those ground loop hum eliminators that are sometimes used by security camera installers do NOT provide ground isolation.
You can verify that with an ohmmeter.
Again congratulations!
__________________
Reply With Quote
Audiokarma
  #26  
Old Yesterday, 11:17 AM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 1,945
Wao. Great sleuthing job! ...Mr. Dragonslayer.

And to think how i used to cuss those with just the intermittent 'griplet' problems.
Reply With Quote
  #27  
Old Yesterday, 11:39 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 6,478
Quote:
Originally Posted by Jeff View Post
Thanks! Whether you find it or not I appreciate the gesture
I still have to get my paypal straightened out.
Evidently you don't need the set anymore. That's alright with me.
Reply With Quote
  #28  
Old Yesterday, 11:52 AM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 6,478
Quote:
Originally Posted by kf4rca View Post
I think that set has a bridge rectifier power supply. So its ground is ground to that set only.
Those sets cannot have an external video input for that reason. Modern sets have a switching supply and the transformer in it provides the isolation for external grounded video inputs.
There are video transformers out there but they are kind of pricey ($22).
Those ground loop hum eliminators that are sometimes used by security camera installers do NOT provide ground isolation.
You can verify that with an ohmmeter.
Again congratulations!
I didn't know you were trying to use an external video source with this chassis. You should've used a modulator that converts a video source to VHF channel 3 or 4. They're all over the place for a buck or two.
BTW, I'm a firm believer in GFCI receptacles. It saved a lot of damage to hot chassis sets when contacting the chassis to ground.
Reply With Quote
  #29  
Old Yesterday, 12:15 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 10,282
That set could work with video injection if you power it through an isolation transformer.... if in doubt as to wether a chassis is hot always power it through an isolation trans.... especially when plan to connect the set to anything that isn't battery powered.
__________________
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
  #30  
Old Yesterday, 03:27 PM
Jeff Jeff is offline
VideoKarma Member
 
Join Date: Oct 2015
Posts: 17
Quote:
Originally Posted by Electronic M View Post
That set could work with video injection if you power it through an isolation transformer.... if in doubt as to wether a chassis is hot always power it through an isolation trans.... especially when plan to connect the set to anything that isn't battery powered.
Oh for sure, how do you think I've been probing it with the scope? Every time I forget to plug it in to the iso transformer, and I hook the probe ground up... BANG! There went another chip
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 07:55 PM.



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