1957 RCA 14" model 14-S-7070 TV set

[TC Chris]

I'll post a photo of your TV's ancestor. It was my parents' bedroom TV, and in the summer it got carted to the cottage. It was a "portable," after all. I learned what that word really meant when was in grade school. There was some big event, maybe the first US satellite, probably something a couple years later, and I got permission to carry the "portable" TV across the street to the grade school so we could watch the big event.

In the photo it is sitting atop the 1954 Zenith, my parents' first TV, that I am trying to re-home (free!!).

Chris Campbell

[electra225]

Uhhhh, I don't see a photo. If I was closer, that Zenith TV would be in my hoard as we speak. I'd like to see your RCA TV picture.

I think I am ready to see if I can let out the magic smoke. I ran the resistance checks again. The TV guys on ARF were making fun of me using an antique VTVM for measurements. As you guys probably know, I own six VTVM's and use them all. I have three hot on the bench anytime my bench light is on. So I was using a digital meter. I got some weird resistance readings, so tried to run them down. Turns out, after wasting considerable time and raising my blood pressure, that the batteries in the digital meter were weak, giving strange, inaccurate readings. The batteries in a VTVM don't go down or get weak. That is why I prefer using a VTVM. I get known accurate readings. The plan is to power up slowly with dimbulb and KAW and hope for the best. I haven't found a new or even a used replacement power transformer as of yet, so I hope the mods I made will work, at least long enough for me to know whether I have a usable TV set or not. If the thing won't work, I don't need to find a power transformer. If it works okay, but if the mods on the power supply fail, I can rest assured that a power transformer is all it needs.

[TC Chris]

Trying again.

[TC Chris]

While we're at it, a Zenith color set:

And a Philco portable with pneumatic channel-changer (left one, right one taken):

Both free....

[electra225]

I like the blue RCA TV set. I also like the little Philco set on the left. Color TV sets are above my pay grade at the present time. I'll never be a TV guy. IF I get this RCA done successfully, it may be my last. The vendors that deal with TV parts are difficult to work with. We are lucky we have Gary at VM Enthusiasts......

[electra225]

Some of the latest pictures.....

[electra225]

Good news and bad news. The good news is it works somewhat. I haven't made any adjustments outside of vertical height and linearity. The yoke needs to be turned so it's straight. The centering rings need to be adjusted, but may be about right if I turn them with the yoke. I have insufficient vertical height. A new high voltage rectifier fixed the picture shrink issue. I don't notice a neck shadow, so I think I have the yoke forward enough. The bad news is my Radio Shack digital meter smoked. I had it connected right. It's been reading weird lately. I have 210 VDC B+ and it pulls 140 watts give or take from the line. The video seems good, audio seems good. Now to figure out why I have a vertical issue.

This is how it looked when I powered up before any adjustments.

[William]

Good news, except for the meter. How did the adjustments go? Where you able to fill out the screen with picture? It won't be long, and you will have fully functional RCA TV.

Bill

[electra225]

I need to move the yoke and centering rings, but that is not my concern. I have insufficient vertical deflection. When the set is first powered up, the bottom 2" of the screen is black, the top of the screen has full deflection, but with heavy retrace lines, then that shrinks after the set warms up and has run awhile. I also notice that I have to turn the vertical hold control fully clockwise to achieve vertical lock. I've been told it might be due to a bad flyback (horizontal output transformer) due to its relationship to the deflection yoke. I would think if the flyback was the issue, there would be a black space top and bottom on power up. I have good horizontal deflection with stable lock somewhere closer to the middle of the control range, so I think I'm good there. The vertical multivibrator (oscillator) and sync amplifier, V4, a 6CH8. The tube in that socket is a 6HU8. There is no sub listed for a 6CH8. A guess theory might be that someone, sometimes used the substitute tube to overcome the effects of a leaky coupling capacitor. Now that the caps are changed, this changes the speed the vertical oscillator runs at, affecting the vertical deflection. I fixed several issues and didn't go backwards, didn't do any harm in the recap, so that is all good as well. This has been a learning experience, and I'l learning a lot. A big advantage I have is that I'm not afraid to make a fool of myself.......

[TC Chris]

There is nothing foolish about undertaking a new task and learning new things in the process. Too many times we hesitate to try something new for fear of looking like a fool. Actually, those of us who kinda hang back usually end up a bit jealous of those who jump right in. One advantage of being an old guy is that nobody regards you as cool anyway, at least on first impression, so you can try things without fear of losing cool status.

Many years ago we had a family reunion in AL when an uncle had a terminal disease. It was on the Gulf shore, a tourist area. We drove past a water slide business and another uncle said "We should try that." I was way too cool for that but figured if an old uncle could do it, I could too, and it was fun. Lesson learned and remembered. Thank you, Uncle Wesley.

Chris Campbell

[electra225]

I just learned that the power supply experiment is not going to work. I just can't get enough power out of half the secondary of the power transformer to achieve full vertical deflection or to have enough power when it sweeps. I fried my digital meter on this TV chassis somehow. I quit monitoring B+ while I was making adjustments. I have given the vertical deflection controls all they could give, wide open, still about an inch from having full deflection. The front end gets wonky at 160 volts B+ as well. I reckon I'll just bite the bullet and put a transformer in it. I can get the rest tuned up and make sure I have a TV set worthy of a new transformer. This is how we learn. I'm not even disappointed. I was hoping it would still be broke after I got the caps done so I could troubleshoot and learn. I'm getting my wish. A new Hammond transformer will cost $150 plus shipping. AES is the highest on price, but I can run up there and get it, then Don and I can hit Ted's Hot Dogs while I'm there.

[William]

Sorry the PT thing didn't work out, but as you said you are learning and then there is a trip to AES and Ted's.

Bill

[electra225]

Well, in spite of fits and starts with this TV set, I did manage to watch a DVD of the Beverly Hillbillies on it this afternoon. It ran probably four hours. I still have a vertical issue to sort. I made progress. There is a LOOONNNGG story about this project, one I may share if there is interest. Yesterday, Friday was one of the more interesting days I have had since I started working in this hobby over 40 years ago.

[TC Chris]

No fair saying "there's a long story." Gotta tell the story.

Chris Campbell

[William]

Yes, please share!!

Bill

[electra225]

I will be researching how the vertical deflection circuits work in this set. I will run some voltage checks, which may give me a clue. The vertical hold control, vertical height control and vertical linearity control are all at their max. The vertical is relatively stable, but it rolls when scenes change and when I connect and disconnect a DVD player or the TV Analyzer. So I think it's fair to say the vertical is "almost' like it should be. I need to find the connection between the hold control and the height controls. This circuit is powered by boost voltage. Is that low? Would a weak horizontal output tube or a weak damper cause low boost voltage? It looks to me like the boost voltage, generated in the flyback, may be rectified by the damper. Then, what effect would low boost voltage have on the vertical deflection circuits? Would low B+ alter the speed at which the vertical multivibrator runs, and would that change in oscillator speed give deflection issues?

[electra225]

I need to examine voltages in the sync, vertical multivibrator, vertical output, horizontal output, damper, and boost voltage circuits. The sync circuits are least likely suspects, but it involves tubes used in the multivibrator circuits. If boost voltage does power these circuits, and if boost voltage is low, then we need to examine the horizontal, damper and flyback voltages to see why. If the voltage is low on the plate of the vertical multivibrator, that will change the amplitude of the waveform impressed upon the vertical output tube. The vertical output circuit behaves much like an audio amplifier. Instead of using the voice coil to load the transformer, it uses the deflection yoke. If voltages are okay, and if tube substitution fails to improve matters, the next step is to scope the various waveforms to see what is amiss. My old Heathkit scope is on the fritz, so that may be a project to be done before I can sort the TV vertical issue. I'm not in a hurry. I have come so far with this set, it's amazing, considering who is working on it. I have a beautiful, well-focused stable black and white picture. The TV guys say establishing a stable raster is the hard part. If so, the hard part is over. I want to sort this issue without throwing parts at it. I want to troubleshoot the issue in an organized and dedicated manner. Boost voltage should be in the 600 volt range typically. The schematic shows 240 VDC for boost voltage. I need to figure out what is right. I've been reading a good text on TV repair that I have and have been watching Shango and bandersen videos. And, the best part is, I have been enjoying the journey and am grateful for the opportunity.

[electra225]

To make a long story short, I believe I have done all I can for this TV set. I changed the vertical output tube and need to get three other tubes that are suspected to be weak. I'm 99% to where it needs to be. I need to move the yoke a bit more and I still have a black stripe at the top of the screen about 1/4 inch wide. Adjustments may not be perfect, but it doesn't matter at this point. I accomplished what I set out to do, had fun and I learned a ton about working on a TV set. I also believe that the vertical deflection circuit in this set is finicky about the condition of components. I'm going to run the chassis for quite awhile before I stick it back into the cabinet.

[TC Chris]

So is it running on the transformer work-around now?

Chris Campbell

[William]

Congratulations, Greg. TV's are way above my pay grade and I commend you for tackling your second TV. Are you going to do something special to the cabinet, a HOT ROD as you call it? Don't forget to share a photo of the finished product.

Bill