Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Transistor Portable Televisions

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 01-31-2016, 09:35 PM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
Philco Safari Vertical Linearity issue

Hello, everyone,

I took a break from working on my Philco Safari, but really want to get it working correctly. I know it's close, but can't get the vertical linearity correct (or anywhere near, really). Approximately the bottom half of the image is scrunched into a white line (at best). The top half of the image is visible but a bit stretched. When I adjust the vertical linearity and height controls, the only way I can see the bottom of the image is if it is folded over and upside-down.

I replaced all the resistors and electrolytic capacitors. I think I may have made a mistake on a value of one of the resistors. I'm hoping one of you may be able to point me at least in the right direction. I checked the values against the SAMS, and can't find the mistake....but that doesn't mean much - may be mental fatigue.

Here is a video of how the TV behaves:

https://www.youtube.com/watch?v=gOphfPjS2JQ

The TV is receiving a signal from a blonder tongue modulator transmitting a signal to the whip antenna. I have a variable power supply hooked to the battery terminals of the TV. At the beginning of the video, the TV is running on low voltage (4.3vdc), and you can see the whole image. However, as the voltage goes up to the operating voltage (~7.5vdc), the bottom half of the image gets squeezed and folded over. I try to adjust the controls at voltage, but there is no way to correct it. As the voltage is turned down at the end of the video, you can see the bottom of the image reappearing.

Thank you guys for your help. I'll post some schematics of the sweep circuits from the SAMs I have soon. I suspect it's an incorrect resistor value, because all the capacitors have been checked about 20 times. lol

Last edited by goat1981; 03-25-2016 at 09:03 PM.
Reply With Quote
  #2  
Old 01-31-2016, 09:42 PM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
Here are some screenshots of the sweep circuits. Thanks again!
Attached Images
File Type: jpg Screen Shot 2016-01-31 at 9.40.03 PM.jpg (122.9 KB, 29 views)
File Type: jpg Screen Shot 2016-01-31 at 9.40.27 PM.jpg (109.5 KB, 37 views)
Reply With Quote
  #3  
Old 01-31-2016, 09:54 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory+Moderator
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,154
I'd check voltages at the transistor pins with the set at reduced ans normal voltages and compare to what the schematic specifies.

Word to the wise whenever at all possible read the value off the original part you are replacing in the set, and NOT the schematic....I've blindly followed sam's and got bit by their numerous typos a few times, and now take all sam's data with a grain of salt.
__________________
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
  #4  
Old 02-05-2016, 09:04 PM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
Cool. Thanks for the reply. I'll check some voltages this weekend.

Are there any specific resistors I should check the values on? Specifically those that may affect the vertical height or linearity?

Thanks again for your help.



Quote:
Originally Posted by Electronic M View Post
I'd check voltages at the transistor pins with the set at reduced ans normal voltages and compare to what the schematic specifies.

Word to the wise whenever at all possible read the value off the original part you are replacing in the set, and NOT the schematic....I've blindly followed sam's and got bit by their numerous typos a few times, and now take all sam's data with a grain of salt.
Reply With Quote
  #5  
Old 02-05-2016, 10:10 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory+Moderator
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,154
Quote:
Originally Posted by goat1981 View Post
Cool. Thanks for the reply. I'll check some voltages this weekend.

Are there any specific resistors I should check the values on? Specifically those that may affect the vertical height or linearity?

Thanks again for your help.
R75-R80 would be prime suspects, but I'd check every vertical resistor (including the pots), and the synch resistors (since the bias of the synch sep affects current flow through the vert osc transformer primary and the osc stage).

Voltage differences (and if you have an oscilloscope, waveform differences) in the vertical stage should help you localize the problem
__________________
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
  #6  
Old 02-06-2016, 10:46 AM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
Excellent! Thank you for the starting point.

I appreciate your help.
Reply With Quote
  #7  
Old 03-22-2016, 04:45 PM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
UPDATE -- please help. :-)

Hello, everyone,

I have had time this past weekend to look further into the Safari vertical distortion issues. Thanks to Tom (Electronic M) for supplying me with a spare sweep board to check for incorrect resistor values (and spare parts).

I was actually hoping that I made a mistake somewhere when replacing resistors (doing this originally because of the distortion issues), but I couldn't find any incorrect values when comparing with the unmodified sweep board and the SAMS.

I tried slightly increasing the value of the non polar capacitors C15 and C17 (see attached schematic), and this actually improved things a bit. I increased C15 from 7mfd -> 10mfd, and C17 from 5mfd -> 6.8mfd. My reasoning was that the original capacitors were a bit high in value to begin with. After doing this modification, there is no more foldover.

However, the vertical linearity is still not correctable with the controls. Please see attached pictures -- this is the best I can do. The top and bottom are pinched and the middle is a bit bloated. I checked all resistors, capacitors, and controls in the vertical circuits, and all are within spec. I also did DC voltage measurements on the transistors in this circuit, and this is where issues came up....

The voltages around the vertical oscillator (X14) were fine -- pretty much what the SAMS specifies. However, the vertical output transistor (X15) had values that were off, specifically on the emitter.

Here are the readings on X15:
B: -.89v (SAMS specifies -.7v)
C: -3.7v (SAMS specifies -4.5v)
E: -.7v (SAMS specifies -.1v) -- !!?

Is it possible I have a bad vertical output transistor that's working but not to its full potential? I have checked every other component in that circuit and am at a loss. There seems to be a replacement transistor out there -- the NTE 121 -- but it's relatively expensive, and am not sure it would work correctly. Anyone have experience with this transistor? Any other thoughts?

Thanks for your help in fixing this TV. I really would like to get it working optimally.
Attached Images
File Type: jpg Screen Shot 2016-01-31 at 9.40.27 PM.jpg (94.6 KB, 12 views)
File Type: jpg Screen Shot 2016-01-31 at 9.40.03 PM.jpg (91.7 KB, 14 views)
File Type: jpg IMG_1721.jpg (38.8 KB, 24 views)
File Type: jpg IMG_1720.jpg (35.3 KB, 30 views)
File Type: jpg IMG_1717.jpg (30.4 KB, 29 views)
Reply With Quote
  #8  
Old 03-22-2016, 04:49 PM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
For some reason I can't get the screen shots to post with the correct orientation. Please orient 90 degrees to the right.
Reply With Quote
  #9  
Old 03-24-2016, 08:00 PM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
Any opinions on using a NTE 121 transistor in the Safari as the vertical output?
Reply With Quote
  #10  
Old 03-25-2016, 12:13 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory+Moderator
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,154
If all R'r and C's have been replaced then it's either Yoke, transformers, or transistors.

Partial failure is possible with early transistors. I have seen early 70's transistors develop weird problems so earlier ones are more suspect.

One other possibility is a problem baked into the factory design....
__________________
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
  #11  
Old 03-25-2016, 02:29 AM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
Quote:
Originally Posted by Electronic M View Post
If all R'r and C's have been replaced then it's either Yoke, transformers, or transistors.

Partial failure is possible with early transistors. I have seen early 70's transistors develop weird problems so earlier ones are more suspect.

One other possibility is a problem baked into the factory design....
Thanks for the reply.

I checked the resistance of the transformer windings, and they all seem to be in spec. Not too sure about the yoke - even though those resistances also check out, I am sure other factors could be at play there.

I suspect it's the vertical output transistor, as that's where the voltage readings are off. I may try the NTE 121 transistor, but I am wary about 'universal' replacements, especially to replace such an early transistor that was specifically designed for this TV...

I know vertical linearity *can* be good - I have seen a couple of sets play (i.e. the Safari that Bob Anderson restored on YouTube) that have very little vertical distortion.

I would have asked to buy that transistor from you, but from the pictures you sent earlier, it looked like it was missing from your parts chassis.

Thanks again for all your help. Any other suggestions are very welcome. :-)
Reply With Quote
  #12  
Old 04-01-2016, 09:34 AM
timmy's Avatar
timmy timmy is offline
VideoKarma Member
 
Join Date: Jan 2011
Location: ferndale ny
Posts: 1,725
Maybe resistor or a cap around the transistor in question, if that transistor was that bad I don't think the pic would even look the way it does. What about the voltages feeding that transistor, if that's low other voltages will be low as well.
Reply With Quote
  #13  
Old 04-01-2016, 09:44 AM
timmy's Avatar
timmy timmy is offline
VideoKarma Member
 
Join Date: Jan 2011
Location: ferndale ny
Posts: 1,725
There are equivalent transistors on eBay to replace the nte121 that will work and I don't think they would hurt anything, after all even those sets have to some degree 10-20% built in, so either way + or - on a different transistor should work. Check data sheets between both transistors, nte121 or another replacement.
Reply With Quote
  #14  
Old 04-25-2016, 12:11 AM
goat1981 goat1981 is offline
VideoKarma Member
 
Join Date: Sep 2015
Posts: 25
An update!

It *was* the transistor. For those of you who like/restore Philco Safaris, it's not impossible for transistors to go out of spec. I didn't really know this (and maybe most of you are already aware of it, making my post less helpful).

I replaced the vertical output transistors with a Motorola 2N1363, which was listed as a NTE121 equivalent but much cheaper.

The vertical linearity is now quite good. However, there is still an overall low-voltage issue that I can't track down.

I recently found a tan/gold Philco Safari in *exceptional* condition, unrestored, that works extremely well. I can't believe the original components are still working so well. All voltages in this set are spot on according to SAMs and the picture is brighter and clearer. It actually has quite a nice picture. I'm a bit at a loss why my black Safari (that I spent so much time on) still has low voltage...maybe a bad power transformer (?)... Oh well, for now, I'll be glad that at least has a watchable picture.

I'll post a new thread about the tan/gold Safari with pictures. It's a nice example!

Thank you all for your help. If any Safari owners know about any reasons for overall low voltage, let me know...
Reply With Quote
  #15  
Old 04-25-2016, 01:59 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory+Moderator
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,154
Glad you got it working!
__________________
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 10:37 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.