Watching my 21 inch 1960 Magnavox the other day, and suddenly the bottom shrunk.

Anyone know which it could be? Tube, Cap, Resistor?

I don't mind trouble shooting, and checking everything,
but I thought someone might be familiar with this problem and put me in the right direction... Thanks for any help!!

Magnavox300

When something happens suddenly like that I generally check for bad tube socket contacts. In your case try wiggling the vertical output tube. Or possibly a dirty vertical size or linearity control. A lot depends on how extensively the set was restored. If it's still running on original caps then anything is possible. Next I'd check for correct voltages on the vertical output pins.

Check the cathode bypass capacitor on the vertical output tube.

And don't dismiss the possibility of "tin whiskers" on one of the vertical controls if the suggestions above don't fix it. I had that happen on an Admiral

Check the cathode bypass capacitor on the vertical output tube.

This gets my vote......

Cap in the very lin. control area,

screen grid cap in V out.

Anyone know which it could be? Tube, Cap, Resistor?



I got to thinking about this one. First, I wondered where a post went where I suggested centering on the vertical output/oscillator sections. Then I re-read the original and realized that the three choices pretty much cover everything about most electronics as there's not a lot left. Its really amazing just what can be accomplished with the tube, capacitor and resistor! And I don't blame anyone for coming here for a good lead in the right direction. We are lucky to have such a plethora of knowledge.

I also was thinking how odd it must seem to some how people like many of us can be so interested in what by today's standards is evidently irrelevant. It is mind boggling to think that they can put 500, or 5000 of my 46 Fada in some silicon microchip. That is amazing, but I find modern technology completely boring compared to what we enjoy. You will never find me lovingly cleaning some 'board' out of some modern device! Guess I'm not heading toward making a lot of money in electronics right! I am a tech now in industry and the guys leaning more toward the software/P.L.C. realm as a personal interest are the guys who will move onward and upward. Sorry, I can make a separate thread on the importance of mastering Siemens controls technology.

Well, it's been a year and a half since I posted this, but i finally decided to try to fix the shrunken bottom of the picture on my Magnavox300.
This is the first vintage TV set I purchased about 3 years ago ...
My Emerson is just not working, no matter what I do, so I thought I would take a break, and get to work on this.
I appreciate the help I always get, and did take a look at all the components in the vertical. I didn't find anything directly in the circuit, but after a few days of looking, I decided to just go ahead and replace the only electrolytic in the vertical, which was a 50uf 50v cap... It tested fine, but I figured I'd replace it just in case it was leaky.
After installing the new cap, I noticed right underneath it, another cap I had originally replaced, and it looked like it was dented or burnt somewhat... I took off the Pos. wire, and tested it and it did not test! This Cap must have burned out, and after replacing it, the picture is back to it's normal height!!

Heres a short video:https://www.youtube.com/watch?v=xODOTakRZYM


I don't know exactly why this particular cap was the problem for the loss of the bottom of my picture... I included a schematic with a circled section, I believe it was C2-B, a 20uf cap.
I also included a photo of the bad cap...
Funny thing is, when I bought this 1960 Magnavox, it worked fine when I got it home even after 53 years! I replace the caps, and one of them lasts only two years!
So... I was wondering if it would be worth actually buying more expensive caps when restoring these sets, like F&T or something similar?

Maybe double check the voltage rating on the cap and what the circuit calls for just to be sure. I always get the 10,000hr 105 deg c caps and have never had one fail.

Gregb

Hey that's pretty good sleuthing, dude. :yes: Besides verifying the voltage rating of that cap, check the value of the two 270K equalizing resistors. If one is off by much, it would throw excessive voltage onto one of the caps, since the caps are in series.

That's the Cadillac Bypass cap we voted for back in Feb....

.

That's the Cadillac Bypass cap we voted for back in Feb....

.Thanks, well I wish I knew more about the terms... I did see you said it could be the bypass cap, and I had those notes with me on the bench for the last few days, but I didn't know what a bypass cap was! I thought I should have been looking only in the Vertical section...
I know I need some more experience, especially reading a schematic, but I still do appreciate all the help!
It's so nice to have the set working like new... Thanks again!
Magnavox300

Hey that's pretty good sleuthing, dude. :yes: Besides verifying the voltage rating of that cap, check the value of the two 270K equalizing resistors. If one is off by much, it would throw excessive voltage onto one of the caps, since the caps are in series.

I believe the voltage rating was correct, but I will check, and those 270K resistors as well!
That makes sense, thanks!

check the value of the two 270K equalizing resistors. If one is off by much, it would throw excessive voltage onto one of the caps, since the caps are in series.
both of those resistors were bad... one did not read at all, and the other was at 750K! That accounts for the excessive voltage and the bad cap. Thanks for that good advise, I would have never known and just thought it was a faulty cap!

I'm pretty sure they are not labeled as Cathode Bypass caps on the Sams, but
they will be called such in service books, amplifier books etc. Books you can get
on ebay or find on google books if you search for vertical output tube circuits.
Sorry I didn't know your level of knowledge when we all wrote about it back in
Feb. We would have been more descriptive, and less technical....
Anyway, it looks like someone was in there before, because they ain't 1960 caps in
your picture ! And it's good ya- got it working quickly !

Nice looking tv, My parents had a similar Magnavox when I was a kid....
I use to love watching the "dot" after you shut it off... Seemed to take 4
minutes for it to go away.... Looks like a similar chassis....

.

Just to be clear - C1 is the cathode bypass cap. It connects to the cathode on the vertical output tube.

The cap that went bad was C2-B which combined with C4 filters ripple out of the boost voltage.

Just to be clear - C1 is the cathode bypass cap. It connects to the cathode on the vertical output tube.

The cap that went bad was C2-B which combined with C4 filters ripple out of the boost voltage.

Okay, so then I did replace the cathode bypass cap username1 originally suggested...
I did see it was the only cap coming off the vertical tube, and even though it tested well, I did replace it... thats when I noticed the burnt mark on the C2-B cap since it was right underneath C1.

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