Newbie's First Questions RCA TS 721 Restoration

[Chris K]

Originally Posted by bandersen

I'd say a lot closer Yes, it is a vertical issue. Looks like foldover and you have way too much height. Remember the viewing area is a 4:3 aspect ratio rectangle - it's not a porthole set. You should have about 1-1/2" blank at the top and bottom.

Reduce the height and adjust the vertical linearity and see where that gets you.

HOLY CRAP! The height pot was the last link in the fold over chain of events. A few hours with Bob's advice and here it is. Thank you so much! Thanks to all who helped over the past several weeks!

[bandersen]

Possibly. I'm also suspicious of the vertical oscillator, output tube and all associated components.

Symptom is very bad linearity. The oscillator should produce a linear sawtooth wave which is then amplified by the vertical output stage. If either is defective, it will distort the deflection.

[Spinning Head]

Wow! You stayed with it through all those bad parts.
Break out your favorite adult beverage and celebrate, just don't mix with HV.

[old_tv_nut]

Wonderful!

[Chris K]

Thanks guys! It feels pretty good. It needs some additional tweaking but where it is now compared to where it was...all I can say is Yippee!

[Notimetolooz]

Yeah, you just have to stay with it. TVs are complex and there can be more than one bad part.
You do have to make sure you are doing things correctly like cleaning pots.
You don't want to make more problems. You might not have done anything wrong but the guy that worked on it before may have.

[kvflyer]

Yes, that looks "Mo Bettah"! Congratulations. I had a problem with my Admiral set that turned out being tin whiskers in the control. A good tooth brushing and it fixed that. First time I had experienced it and I was surprised, but pleased.

[Chris K]

Originally Posted by kvflyer

Yes, that looks "Mo Bettah"! Congratulations. I had a problem with my Admiral set that turned out being tin whiskers in the control. A good tooth brushing and it fixed that. First time I had experienced it and I was surprised, but pleased.

Those Admirals grew whiskers like Santa Claus! I wonder what kind of metal alloy they used where that was such a common problem across so many TVs for so many years? Thanks for the congrats!

[Chris K]

Originally Posted by Notimetolooz

Yeah, you just have to stay with it. TVs are complex and there can be more than one bad part.
You do have to make sure you are doing things correctly like cleaning pots.
You don't want to make more problems. You might not have done anything wrong but the guy that worked on it before may have.

Oh I screwed the pooch...no question. The set was virgin. You can only access the insides of the rear adjustment pots for spray cleaning by removing them. There's no access from the front and I ended up not having to replace the vertical height control. About half an hour of spraying and twisting did the job. It's clean and smooth now from 2.4 megs all the way down to next to nothing. The entire chassis is now rewired, recapped and clean. Next mountain to climb is the sound. It's working as I get crackle but no processing of a signal from the generator. This set's a bear! Fighting me to the last tube, coil and transformer!

[Chris K]

Gotcha...thanks everyone for the advice and insights. This is a great place to learn... particularly if you're willing to embarrass yourself!!! Seriously, this restoration and the interaction with the experts here has taught me so much. It's very appreciated!

[Penthode]

What are you using for a,signal generator? Where,are you injecting the signal? Can you outline what you are doing with the equipment used?

[Electronic M]

The AM signal generator method kind of relies on old TV/radio service tube era signal generators with crude dirty modulators (at least if you want the detector to have output to hear and measure). Basically the tube era modulators distort the carrier enough to create a form of FM modulation along with the AM modulation.* Modern SS generators often don't have that useful distortion, and even some of the high end laboratory grade stuff from the tube era lacked it.

Easy way to check for it is to take an analog FM radio and feed it 10.7MHz (nearly universal FM IF frequency) or something in the FM band if the generator goes that high and see if the radio produces the modulation tone.

* In some cases video buzz in the sound of vintage sets is created from a similar effect where over modulation of the AM video carrier creates FM noise the TV can demodulate...I've described this in-depth in other threads before and don't feel like doing it again right now ( after midnight).

[Penthode]

What is being used as a signal generator? How are you achieving frequency accuracy?

How do you know the generator is producing a signal?

Is it modulated?

I would like to see justification why you feel the audio channel is not working.

[Chris K]

Originally Posted by Penthode

What is being used as a signal generator? How are you achieving frequency accuracy?

How do you know the generator is producing a signal?

Is it modulated?

I would like to see justification why you feel the audio channel is not working.

For the crosshatch pattern I'm using a Leader LCG-396 that I have tested on a Zenith 12" Sidekick I restored. There's an audible tone that accompanies the crosshatch pattern. I'd have to look up the frequency...probably 1KHz. Last week, I injected an audio output tone from a Knight KG 650 RF generator (range 160 KHz to 115 MHz for the RF...I don't know what the audio tone frequency is) all the way back to the output of the discriminator 6AL5 and got a loud audio tone from the speaker that responded to volume pot changes so everything from the volume control forward is working. The problem has to be in the RF circuit correct? Now, this morning I ran the pattern generator into the set and I could hear a very low 1KHz tone coming through the speaker that responded to volume control inputs but when I say low output, I mean I needed to put my ear close to the speaker to hear it...but it was there and that's the first time I've heard it.

As for injecting carrier signals with information into the RF circuitry, that's about where my knowledge base stops. I made some idiotic attempts to get something out of a carrier signal input to the RF circuit but they are not worth mentioning for the purpose of troubleshooting analysis.

Another potential issue for the future...I did try to input a digital over the air broadcast signal through a digital to analog converter box into the TV. It's a commercial unit I've used before on my other vintage TVs and it works OK. On the 721, I wasn't getting a discernable image just some image jumps and flashes when I changed channels on the converter box. The pattern generator injects images fine but my guess is I'm going to need some sort of a signal boost if I'm going to watch anything other than a crosshatch pattern. That's for another day.

[Penthode]

Originally Posted by Chris K

For the crosshatch pattern I'm using a Leader LCG-396 that I have tested on a Zenith 12" Sidekick I restored. There's an audible tone that accompanies the crosshatch pattern. I'd have to look up the frequency...probably 1KHz. Last week, I injected an audio output tone from a Knight KG 650 RF generator (range 160 KHz to 115 MHz for the RF...I don't know what the audio tone frequency is) all the way back to the output of the discriminator 6AL5 and got a loud audio tone from the speaker that responded to volume pot changes so everything from the volume control forward is working. The problem has to be in the RF circuit correct? Now, this morning I ran the pattern generator into the set and I could hear a very low 1KHz tone coming through the speaker that responded to volume control inputs but when I say low output, I mean I needed to put my ear close to the speaker to hear it...but it was there and that's the first time I've heard it.

As for injecting carrier signals with information into the RF circuitry, that's about where my knowledge base stops. I made some idiotic attempts to get something out of a carrier signal input to the RF circuit but they are not worth mentioning for the purpose of troubleshooting analysis.

Another potential issue for the future...I did try to input a digital over the air broadcast signal through a digital to analog converter box into the TV. It's a commercial unit I've used before on my other vintage TVs and it works OK. On the 721, I wasn't getting a discernable image just some image jumps and flashes when I changed channels on the converter box. The pattern generator injects images fine but my guess is I'm going to need some sort of a signal boost if I'm going to watch anything other than a crosshatch pattern. That's for another day.

I thought you were attempting to inject a 21.25MHz IF signal to test the audio chain.

Do you understand how the RF IF system of this set works. It is a split sound design and if the tuner local oscillator is way off, you will get no sound.

The alignment of a split sound set is more critical than the later intercarrier sets as the sound IF/ discriminator has to be precisely aligned with the Video IF otherwise you get good sound and lousy picture or good picture with no sound. Also in the split sound receiver, you always use the tuner fine tuning control to adjust for best sound and not best picture.

I you are not familiar with split sound vs intercarrier sound systems, this forum will help enlight you.