Rca 730tv1
 

I posted a question about this set on another thread but I figured I would make a thread for the set and keep it all in one place. This is my second ever restoration and it is going 100 times faster than my first. I've recapped the chassis, fixed a problem with the flyback, and replaced the megohm resistor between the HV rectifier and the crt anode that had drifted WAY high. To my delight the set is producing a picture :banana:. My next hurdle to tackle is a vertical linearity problem. I'm going to go hunting in that area for any out of spec resistor and check the height and vertical linearity controls for spec. There is a video link below that shows off the problem very well.
http://www.youtube.com/watch?v=zK56_...MFlODWfOTpscLd

Hmmm... can't easily see a vertical linearity problem in your video. That's much easier to see with a test pattern.

Things to look for:

- drifted resistor values
- wrong capacitor values (double check your replacements, and don't use ceramic disks)
- weak tube
- bad potentiometer

Yoke or vertical output transformer issues usually have more severe symptoms, although I have seen a case of a leaky vertical output transformer (leakage between primary and secondary) which caused subtle problems in the vertical system.

It is much easier to see with the test pattern below. No time tonight for poking around under the chassis but I thought I'd post a picture of progress so far.
http://farm8.staticflickr.com/7153/6...38c297496d.jpg

Using the numbers from the Sams on

http://www.earlytelevision.org/tv_sc..._diagrams.html

A logical order to test:

Check or substitute V14.

Check voltages on V14A & V14B.
Note: Remember that on this tube you are not measuring to chassis.

On V14B:

Check C58, C57 for leaking, if replaced check for correct value and for leakage.

Check R67 for correct value.

And the two electrolytics, C2 and C1, check by jumping.

Also jump C3 across the height control.


My best guess is that the big fat C58 going from the vertical osc. plate to the high resistance grid of the vertical output is leaking.

C58 originally was only a 200 volt, I'd go at least 600 on this one, as a little leakage here can give the vert output a very hot plate.

C57 originally was a 1000 volt.

James.

Looks to me like you have a horizontal width problem, not a vertical linearity problem...??

John,

You are 100% correct!

With only the image of the test pattern visible and the height stretched, I had assumed that the RCA roundie was flipped on its side for under-the-chassis checking, but a quick enhancement of the picture to see what is hidding in those shadows reveals that this is not the case.

Let's see if I can undo my rather large goof.

On page 24 of the Sams, you will see the horizontal adjustments.

I would suggest checking or replacing your 6BG6 and then trying (count your turns so you can undo any changes) adjusting the horizontal linearity and see if that helps. Warning: These linearity coils sometimes freeze with age and if forced, you can break the tube. I would suggest a gentle test wiggle with the power off, so you can feel if the core is stuck or not.

If this adjustment seems to be addressing the right problem, and you have recapped and and tested all the tubes in the horizontal section, you might consider doing all the procedure on page 24, with this warning: A mistake in doing the horizontal oscillator adjustment can sometimes be very difficult for a learner to resolve.

James

I think it is me that made the rather large goof, not you James. I thought the picture was stretched vertically so I misdiagnosed the problem as vertical linearity. I did not recognize that the picture could instead be squished horizontally, and therefore a horizontal problem. Interestingly enough when I adjust the width, as well as the horizontal linearity slug there seems to be no change to the picture. Both turn easily and were not stuck at all. The horizontal linearity coil looked a bit melty from the start and I suspected it might be problematic when I first laid eyes on it.
http://farm8.staticflickr.com/7030/6...04312ecfe7.jpg

Width Controls seem to vary in sensitivity from brand to brand, set to set, etc.

The RCAs that I own of that same vintage (721TS, 721TCS, 630TS) seem to need quite a few turns of the Width Control before you get any change.

Now, my 1950 Zenith 12" Porthole, with the Width Control on a slider, is way more sensitive. You breathe on it and you get a change.

I'll give width another shot when I get back in front of the set.
Thanks for the first hand knowledge, it makes things easier and less scary for sure.

Don't be scared by a little bubbling on the wax around the coil. The big question is whether the windings have continuity and whether the adjuster has any effect at all.

Horizontal linearity is one of the more difficult things to get right on certain TVs (difficult for me, anyhow). Your linearity is noticeably off when viewing a test pattern. I doubt it is half as noticeable if you are simply watching a movie or TV show.

I would follow the instructions in the manual, as suggested, and then see how it looks.

Phil Nelson

I suspect that all that is wrong is the 6BG6. Try substituting a new one.

You aint kidding!
Gosh did I get my self in trouble while trying to go through the oscillator adjustment. The width is much closer to being correct but I've completely destroyed the picture in the process.
I've given up for the evening because I started to get frustrated and will pick it back up tomorrow. An opportunity to learn oscillator adjustment thoroughly through thoroughly messing it up :).
Edit: I have three horizontal output tubes, the two that tested good gave me pretty much the same results, another that I was unsure of gave me a severely degraded picture.

Coming back fresh made a big difference. I dialed in the horizontal and figured out my problem. This is my first round screen set and I didn't have an idea of what the final picture dimensions should be. I measured the bezel on the cabinet and realized that I had the picture stretched out WAY too far vertically. After I dialed back the vertical size the picture became much more linear. It's still not perfect towards the top of the picture (as you can see by the clock at the top), but it's close enough for me to watch some movies on it and put it back in the back of the restoration cue and move on.
http://farm8.staticflickr.com/7162/6...1653b358a6.jpg
I installed the chassis into the cabinet and now my favorite TV in my collection is a working TV :banana:.
http://farm8.staticflickr.com/7170/6...9b0c0af10c.jpg

That set looks scrumptious, and so does your avatar! :yes:

Your set looks great. I can't really tell from the clock in your picture that the vertical linearity is off by much.