Left the TCS on for three hours without a signal and blew the flyback, a 47pF Mica in the Horizontal Freq, and a 2 watt resistor. The resistor saved the rest of the chassis by blowing itself up.

Bob, a friend of Henri and myself, troubleshot the chassis, and replaced the aforementioned parts. He suggested I replace all the micas in the Horizontal Locking, Drive and Frequency circuits, and I did that.

Seems to run just fine now...




"Nothing but Static and Heil Hitler...!"


"No! Don't take out those Family Photos...!"


"You getting any of this, Waco...?"




"Well, I'll do your thinkin' for you...!"

Today I'm going to take the TCS's little brother, the 721-TS tabletop model, down into the lab and replace all the micas in the horizontal circuits.

It looks like from now on we should replace all horizontal circuit Micas as a matter of routine - just like Tubulars and Electrolytics. The Experts here are right. They really take a beating, and in the sets I'm working on, are over 60 years old. They probably led to the flyback getting wiped out.

To quote mob boss Remo Gaggi in "Casino"..."Why take a chance?"

Timely advice, since I just started on my 721TCS. I see that cap, part of a clump of six micas on the drive, locking, and frequency adjusters. This will give me something to do while waiting for other parts to arrive in the mail.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Agreed. I've been changing micas in the sync separator and sweep circuitry for the last year or so on all the sets I restore. Seems to be a good preemptive strike.

I do not change micas in the RF or IF stages, as I have yet to see a single failure there in quite a number of sets that have passed by my bench in the last few years.

Be sure to get 1000 V micas for a few places in the circuitry that put rather high voltages across the cap. I found out the hard way that micas do not have a lot of headroom above their rated voltage.

Also note that a lot of micas you can buy are rated only at 300 VDC. It pays to look for 500 VDC for the majority of them, and 1000 VDC for selected cases.

I cannot find a source of 2000 VDC rated micas. I've been wondering if ceramic disks might be a good choice for micas that feed HV pulses back from the flyback to horizontal oscillator. Another place I see 2000 VDC rated micas in the original is in the sweep circuitry of Motorola electrostatic sets. So far 1000 VDC micas work OK there, but I am nervous since originals were rated at 2000 VDC. (These are not the sweep coupling caps to the CRT, which are of course 6000 VDC tubular caps).

Yeah, Tom. There's a 5pF 1500V rated mica near that horizontal section that I didn't replace, as I couldn't find a direct replacement. I left it alone. Hope it's not too critical. I found 1000V micas for the other values where needed. 500V for the rest.

The adjustable micas in the Horizontal Section (C136 A,B, and C I believe) I wonder about the durability of those... ?8)

Blew the flyback by leaving the set on with no signal?

Don't think so.

I've never had to replace a mica trimmer capacitor, except in a few cases where the poor thing had been mechanically beat up. They seem to hold up well.

A typical horizontal drive trimmer doesn't get too much voltage across it. Not sure what the voltage rating of a typical mica trimmer is, but they don't seem to get too stressed.

By the way, I should place a caveat on my statement above about not replacing micas in the RF and IF stages... By that I mean I don't replace molded mica caps in those circuits. As far as fixed wafer micas (generally with no coating) inside IF transformers, I replace them when they show signs of failing, which is often! Most often encountered in the sound IF in TVs and FM radios. I'm not to the point of pre-emptive replacement of them, simply because it is quite labor instensive. Often the value is not known, and one has to experiment to get it right.

Why not? That's how it happened.

I turned off the DVD Player feeding it, after watching a movie. Didn't turn off the TV Set. A few hours after that I came back to the Set. A very faint, high pitched ringing sound, and a wierd "ozone" smell. No raster, melted flyback. Probably on for 4-5 hours total.

Where did you get yours, Phil...?

That may be an example of the old Post hoc, ergo propter hoc fallacy. It may have failed when you happened to run it with no input signal, but should not have failed simply because of there being no input signal.

At least that's the theory. Stranger things have happened, of course.

Oregon. Long drive, but it was an excuse to visit Powell's bookstore and stay at a favorite Portland hotel on the way.

The seller remembers watching it as a boy. Grandpa had a radio/TV shop and kept this after everything else was gone.

Clean, and the CRT tests very strong. Cabinet has a few minor boo-boos on the front. No back cover, but I don't obsess over those. I imagine RCA could have used the same cover as for the tabletops.

Phil Nelson

I doubt very highly that a lack of signal would cause it to fry. A horted turn in fly back is more likely.
I keep warning you guys.
NEVER, EVER, NEVER leave an unattended tv playing alone!!
NOT a good idea!!!!!
The horror stories I've seen in 45 yuears would scare the living daylights out of you!
Example.
About 1968 Craig brought in the chassis for a 1966 Sylvania 25" color tv that had just had major work done on it the previous year.
The customer was in the bathroom shaving, and, smelled something burning. He arrived to his smoke filled living room to find the tv well involved in flames while it still had audio.
Called fire dept. It had caught curtains on fire.
Alot of cabinet dammage.
The company replaced wood case, and, insurance paid all.
The flyback had failed. Didn't burn out hv fuse.
overheated, and, caught on fire.
When I got my instructions it included removing hv cage, chiseling off remains of all hv parts, including flyback, hv ret. socket, regulator socket, focus assembly, etc....
Craig replaced all the above, polus coils, resistors, focus control, alot of wirring, and, destroyed tubes.
We got the set playing again, but, it csot the insurance companny a bundle. That flyback alone was expensive.
The motto of my story?
You no keep an eye on set while on, you are looking for much trouble.
Let me see. How about another lesser example?
My family set. This would have been after my father died, so, perhaps in 1962??
My mother was in the bathroom getting ready for work. I was getting ready for school.
I walked into living room. TV was on.
Suddenly, I heard a loud pop, picture tube went black, and, set made a horrible burning odor. I turned set off, and, warned my mother. She turned it back on. No picture.
She turned it off, turned set around. They removed hv cagte door, and, looked inside. The 6BG6 horizontal output had had a melt down, and, blew up. The glass had a big hole in it, and, plate looked nasty.
Later that day my mom bought a new tube, and, installed it. Luckily, that solved the issue, and, we got the picture back.
Again, if I hadn't been standing there when it happenned, who knows what would have happenned????
Bill Cahill

Nice set Phil. Walnut, right?

Mine came complete with the back screen. It is identical to the tabletop model 721TS, which is repro'ed, BTW. Those tapered, slotted round head wood screws that secure it are available, in brass, at Home Depot in bags of six. I spray them satin black.

I think you're going to like it. It's my favorite set at present. After the recent repairs it has a sparkling good pic, and even the sound is good. The tall cabinet positions the CRT for easy, across the room viewing.

It's an easy electronic resto. Considering your cabinet is in good condition you should have an easy time of it overall.







Have fun...!

Yes, the chassis seems to be well built, nothing too cramped. The cabinet does look like walnut, apart from the photofinish on the frame.

I had sworn off consoles for a while, but this would make a nice companion to the Capehart-Farnsworth 661-P I'm finishing up. Both are narrow 10-inch TV-only consoles. Plus, I'm interested in comparing the engineering.

Phil Nelson

[/quote]That may be an example of the old Post hoc, ergo propter hoc fallacy. It may have failed when you happened to run it with no input signal, but should not have failed simply because of there being no input signal.

At least that's the theory. Stranger things have happened, of course.[/quote]

Yeah, it simply failed. Whether it had a signal or not was academic.

Good things came out of it. Before it crapped out, it had minor horizontal "issues." Little lines and snaps. Repaired, with all new Mica caps in the horizontal section, it's a cleaner, better performing TV.

So is it's little bro, the TS...

Lee

The picture looks great, in fact superb! Glad to see it running again. beautiful wood restoration too.

Steve

Hey Steve...what are you up to? What's on yer Bench?

Hi Lee

I'm in a holding pattern, paying for kids college and it's taking all my spare cash at the moment. My next restorations is going to be the DuMont doghouse but I also have the Philco Safari coming too. Next week I'm heading out to the Midwest to do some planetarium work.

What Are you up to?

Steve

Steve

I'm working on a set right now with a similar problem. Everything works very well, but the horizontal sync is a little unstable. After eliminating basically every other possibility that I can think of, it's down to the flyback transformer. I see some evidence of intermittent arcing internal to the flyback. Ordered a new flyback last week, and I hope the cure is as successful as it has been for your set.

I have personally witnessed this on my DuMont. It would magically work when a screwdriver was placed on the lug of the IF transformer because the capacitance of the screwdriver took the place of the one that had failed in it. I can also say Tom Albrecht is pretty darned good at guessing the capacitance value fro replacment

Good fix on the RCA Lee! Keep it up!