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 Post subject: predicta tv vertical problem
PostPosted: Sep Fri 22, 2017 6:41 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16300
Location: ID 83301
Hi . I am working on a 17" typical predicta . I recapped it and it worked fine . Sitting watching it and 1/3 of the bottom of the screen shrunk upward and stayed . I have tried about everything and no go . I have another set here that works . I swapped the 2 couplets near the vert tube along with the vert transformer , yoke , and went over all my capacitors . Tested voltages on vert tube in both sets and they are very close . Checked the vert height adjustment controls , jumped resistors and capacitors for any reactions . Are there some parts away from the vertical circuit I am missing . Tried to post pic. But won't work


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Fri 22, 2017 7:23 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16742
Location: Albuquerque, NM 87123
Did you test the yoke and the capacitors going to it?


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Fri 22, 2017 2:42 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
Posts: 629
Location: Pewaukee, WI
Did you replace the cathode lytic of the Vert output, and if so are you sure the replacement did not fail? Usually when I see the bottom fold up on any tube TV it is that cap that is causing/or substantially contributing to it.


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Sun 24, 2017 1:19 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 753
Location: Southwestern,Ontario Canada
Are you sure the swapped couplates are any good ? Usually they are junk, just like the other capacitors. You can build new ones on perf board (the type with holes in it) using individual components. Check out Bandersentv videos on Youtube regarding the predictas.
He builds his own, maybe you could contact him,... as his does make, and sell them.
Tony


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Sun 24, 2017 2:19 am 
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Joined: Aug Thu 20, 2015 3:09 pm
Posts: 509
Location: Albion, CA, USA
+1 on Bob's couplates. I got some from him and they work great. He also shows making them in his videos in detail.


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Fri 29, 2017 7:11 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16300
Location: ID 83301
Hi . I used couplets out of a good working set . I plugged the whole pic tube yoke head into the working set and its OK too . It still has the original metal cap cans . I jumped in new caps and still no luck .


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Fri 29, 2017 11:30 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 753
Location: Southwestern,Ontario Canada
Does this set have the transformer, or is it an earlier transformerless set ? You could check the vertical pot (it is a special one with an internal "tap point" on it.) The one located on the very back of the chassis. Sometimes these pots go bad when the vertical tube "goes out" it will take the "pot" with it. You might try subbing in a different "pot".
Tony


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Fri 29, 2017 2:29 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
Posts: 629
Location: Pewaukee, WI
Ken G wrote:
Hi . I used couplets out of a good working set . I plugged the whole pic tube yoke head into the working set and its OK too . It still has the original metal cap cans . I jumped in new caps and still no luck .


If the original cans are leaky or shorted and causing the problem, then 'jumping' new caps in parallel with the bad ones will not fix or reveal the problem. Unless you have a vintage cap tester (such as a Heathkit C3) that can check for leakage at the full rated voltage of the can; You should change the can caps as a matter of practice....Or at the very least change the cans now that you've confirmed it is not working %100 with them installed.


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 Post subject: Re: predicta tv vertical problem
PostPosted: Sep Fri 29, 2017 11:34 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 2993
Location: Florida
Years ago I had a Bendix that would pull up from the bottom after being on a while. All voltages checked out fine. The problem turned out to be a resistor that fed B+ to the vertical output. It checked ok when cool but would increase in value as it heated up. This limited the yoke current (sweep goes from top to bottom of screen) and resulted in the pull up.

RRM


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 Post subject: Re: predicta tv vertical problem
PostPosted: Oct Sun 01, 2017 7:17 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16300
Location: ID 83301
Thanks for the helps . figured it out . these early circuit boards with tubes were a bad idea but ........ The vert tube pin 1 or 9 goes over to a pin on the edge of the board marked vert Lin one wire runs clear across the chassis to a tall 3 cap can 100- 50 section the wire wrap in the circuit board pin was corroded and gave out . soldering it returned the bottom of my picture . I then continued the restoration .

I then jumped that 3 part can with a new cap and discovered it was weak . someone mentioned that never can work . in my 50 years of this it always has for me . its my way of testing for weak caps to decide rather to replace them and my way of doing ng things .


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 Post subject: Re: predicta tv vertical problem
PostPosted: Oct Sun 01, 2017 7:24 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16300
Location: ID 83301
New issues . I'm working on 2 chassis . one is doing fine . the other ones picture is stretched slightly in the middle 1/3 . top & bottom look shrunk a bit . other chassis is not this way .


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 Post subject: Re: predicta tv vertical problem
PostPosted: Oct Mon 02, 2017 5:40 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 2993
Location: Florida
Ken G wrote:
.......
I then jumped that 3 part can with a new cap and discovered it was weak . someone mentioned that never can work . in my 50 years of this it always has for me . its my way of testing for weak caps to decide rather to replace them and my way of doing ng things .


I have a couple of electrolytics with wire leads and alligator caps that I use for this. Bridging an old cap with a new one as a permanent fix is not generally a good idea although it used to be a common practice in repair shops.

RRM


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 Post subject: Re: predicta tv vertical problem
PostPosted: Oct Mon 02, 2017 4:16 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
Posts: 629
Location: Pewaukee, WI
Ken G wrote:
I then jumped that 3 part can with a new cap and discovered it was weak . someone mentioned that never can work . in my 50 years of this it always has for me . its my way of testing for weak caps to decide rather to replace them and my way of doing ng things .


Caps fail two ways: Open or electrically Leaky/shorted. Jumping only finds open caps. If a cap is shorted or leaky (many caps are) jumping won't find or fix the issue.

On sets that have been dormant for years, and repair jobs where jumping has been tried and all parts have been changed or properly tested except the caps, and the set still does not work, just change the cap (or test it at rated voltage if you can).


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 Post subject: Re: predicta tv vertical problem
PostPosted: Oct Tue 03, 2017 5:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16300
Location: ID 83301
Hi, yes . Been at this for 50 years . Know about caps & all . These were my first TV sets and was looking g for short cuts from others . Thanks


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