I suspect you got bit by a random failure of some part, or a tiny
piece of solder from a recap lodged somewhere it wasn't supposed to be.
I had one of those each happen with my CT-100. No fireworks, however,
just no picture.

Wouldn't be the first time that a NOS or well used tube has suddenly cracked/gone gassy or shorted on turn on, especially if it has been subjected to a few bumps 'n thumps such as turning the chassis over for repairs. That's my hunch anyways.

jt

I did check the tube. Although nearly flatlined after that meltdown, the tube wasn't shorted.

Anyone wanna fix this for me? I'll ship you the chassis and pay dearly :D

There is a possibility that the sparks/fireworks sparks flying around in the tube were the remains of whatever shorted (grid wire perhaps) and the short was cleared at the expense of 2 smoked resistors and a dead tube. I guess that I would replace the resistors and tube (and at least check the cap between the two resistors) and try again. carefully!

jr

I can do that. At least I'll know what to half-expect ;)

Naturally I'll run through the tubes, and any component connected directly to the 6BG6. Anything else I should test or look for before another attempt? Aside from wires touching :eek:

From the failed parts it looks like no drive to the horizontal output causing extreme saturation of the tube. It's overload roasted the resistors. Can you scope the control grid on the HOT with the cap off temporarily to see if the drive pulses are present?

I just invested in a scope about six weeks ago, an RCA WO-33A. However, as of yet I don't have a clue how to use it, so no.

Learning how to use the scope is on my to-do list.......

Those are cute little scopes... I keep a 3 inch Heathkit OL-1 as a nostalgia piece, such scopes would be fine for detecting the 15 kHz signal at the grid of the horizontal output tube. Does it work? Can you get a green line? Any response if you touch your finger to the vertical input? (like a 60 Hz sine wave) Those scopes are easy to operate, perhaps we can talk you through it?

jr

You can download the manual here:

http://bama.edebris.com/manuals/rca/wo33a/

Not the greatest scan, but you can read the basics.

I have a WO-33A, unrestored and missing the probes.

http://antiqueradio.org/art/temp/RCA...Unrestored.jpg

My everyday scope is a much newer item. I haven't attempted to use this one for practical work; no doubt it would benefit from some service.

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

I'd love you! :D

I actually have the RCA factory manual for it as well. Seems to work just fine, from a cursory plug in and adjustment.

So it would seem that you are at least to "first base" here, and can get a trace of reasonable brightness and focus positioned on the screen... let me ask "what controls are you unfamiliar with?"
Do you have the matching probe?

jr

Yeah, the average tube era scope is not harder to set up than a monochrome TV that has had all it's user controls cranked to random positions by someone lacking knowledge/courtesy...

The good thing about that little RCA is if you accidentally get across raw RF (damper or some other high voltage pulse) you won't have to start digging thru the vertical input amplifiers for fried protection diodes or worse!

Basically, I'm not familiar with using it in any application nor do I know what I'm looking at when I see it. I have universal probes here, basically just wires with probe ends. Nothing else.

Come to the ETF convention and have somebody show you how to use one.
They could have a workshop.

A calibrated scope is THE #1 tool for TV service. Second is a resistance-capacitance meter. Voltmeters (preferably analog) are third, since many charts list DC only and
its not always easy to figure out the DC average from a calibrated
scope trace.

A multimeter will, however, be used much more than an UNcalibrated
scope, which will still solve TV problems quite well.

Okay, we're back on this set. Some interesting developments....

I replaced the 82 ohm resistor that burned with the same 1 watt, figuring that if it was going to burn up, I'd rather have that resistor burn up than have the resistor hold and damage something else. Everything else under the chassis spec'd out fine.

Now while I was under there, I looked at the Synchro-Guide pot and noticed, whoa, the slug's turned in so far that it's not sticking out the side!! I proceeded to turn the slug out so that it would. But wait a sec, there was nothing wrong with the horizontal!!! Damn!! I shouldn't have touched it!!

THEN I noticed that somehow I forgot to do a filter cap. What?? It's the one with two weird values, 250 uF@ 10V and 1000 uF @ 6V. Centering control bypass caps. Well, the picture did center out, so I'll order those on my next order.

I backed it out to where I thought it was, and then I noticed that the nuts holding it in place were loose. Well hm, I wonder if that's not the original one.

I proceed to put the set back together with a new horizontal output tube, and though I can't explain it, it came back to life! But now, I've got inadequate width, and the width control seems to do nothing. That aside, I've got a very predictable multiple image situation because like an idiot I screwed with the synchro guide control from the underside.

I have a feeling that I'm going to have to just use a plastic handled screwdriver with the chassis sitting on its side and the picture tube held in a jig of some kind in order to get the synchro-guide control to come back into range and have just a single image. Or, can I set it withing a range by resistance?

Another instance where using a scope would be handy, but let's disregard this for the moment as I have to get my hands on a proper probe.

The width, that I'm not sure about. I think that the yoke might have slipped back on the chassis because I had to adjust it back forward in order for the picture tube to hold in the cabinet. Maybe that has something to do with it as well?

But at least I'm back to something I can work with.....

now thats horizontal, it happened to me but the horiz hold pot was turned to much one way so backed it up it was good. but the width, i got that now swing the horiz hold all the way one way then back it up and see it it fixes itself. maybe the pot, they burn too. the hold and or the horiz size.

Does the manual for your scope show a schematic representation of the probe, and it's contents? If so you could probably make a half decent probe out of what is in your junk box. You don't need an exact probe and exact waveform amplitude to adjust the synchroguide. All you need to adjust it is an image of the wave shape with relative amplitude (one peak of the wave form to another) so you can get the point and the hump adjusted to the same height.

The manual describes two probes.

One is just 3-4 feet of RG59 (or 6 or even 174) with clip leads
for ground and center conductor.

The other is a 10x probe. This has a 9 meg resistor in parallel with
and 8 or 10 pF ceramic or mica cap between the cable center
conductor and the clip. The cap is critical if and only
if you need reasonably flat frequency response, which that
scope may not be capable of.

To check scope frequency response, look at the waveform
on the video out of a DVD player playing a frequency
burst or sweep pattern.

So here's where I'm at now.....

Have inadequate width, and horizontal foldover. I have the chassis out on my bench flipped on its side, and the picture tube held in a makeshift test jig. Width control does squat.

This pic is about the best I can get it just by turning the synchro-lock and horizontal hold. Getting the feeling that what I was doing with the synchro-lock in an earlier post wasn't the problem....I think I might have taken something else out with that spark show.

Now what HAS changed is that I now have a Tektronix T922 dual trace scope at hand with probes, so I can scope the waveforms if needed. Problem is that I don't know how :D . This is a really good opportunity for me to learn, as I have the set ready to test, and the equipment to do it. If I need to.

So, that said, advice as to where I go from here? :)

Okay, well, y'know.....if you looked at my last post and said "look at the schematic, stupid....the answer's right there!!!"....well, you'd have been right.

I was wrong in assuming that it was one component that failed that I didn't catch. I decided to start just by looking at all the resistors in the affected systems, and go from there, thinking that the meltdown just overloaded a bunch of stuff. Tested the resistor to the width coil, found that it had doubled in value, and what do you know, I got some width back. Not all of it, but some.

I'm just going to have to go through each resistor in the affected systems, and test and replace them one at a time. Patience and persistence will win this battle.....

Interesting though that I have multiple horizontal images at this point. At least the vertical locks in solid. Now I have the exact opposite issue from when I started this thread.

You have no mystery, With several images on the screen you have a horiz osc.
running too fast.... = Capacitor in timing circuit too small....

Charging and discharging too fast, this often makes the peaks smaller, and a higher
possibly 2X frequency means the next stage is being fed something it's not tuned
for... So it's response is, and should be lower... = narrow picture....

.

Since I didn't change any of the caps in that section from the very first picture in the thread where the horizontal was fine, it's possible that one of them got damaged or taken out in the "event".

Here's some gemane info from RE - I've encountered similar problems with the synchroguide oscillator before, but always lucked out with simple fixes, either the tube or a ceramic cap drifting.

Off frequency could also be caused by a broken slug (core). Is the S-G core good?

L-C or R-C it can be the other part of the timing circuit, not the cap....
I don't remember "the Event" just some free time, looking at the pic.

.

Basically the 6BG6 went up in a shower of sparks with sparks underneath. True cause is still unknown.

I'd imagine so, it turns freely and was good when this whole fiasco started. I've also checked the micas on the S-G (albeit with a Chinese hand held tester), and all caps off the 6SN7 and 6BG6. Everything there is good, including the tubes.

I read the articles, and it seems that perhaps I could do the adjustment with a scope. I do have one handy now, just need some guidance on doing it :)

As far as getting familiar with using the oscilloscope, do you have a square wave and/or sine wave generator? Some scopes like the Tektronix have a built in square wave source available on the front. It helps if you start out with a known signal source. By varying the frequency and amplitude on a generator you can see the effects on the 'scope. The fixed source on a scope like a Tektronix is used to check the adjustment of the trimmer on a 10X probe. That trimmer adjusts the high frequency response flatness.

At this point I have checked everything in the entire horizontal section. Every cap, every resistor. Found a couple resistors that were 150-200% out of tolerance but still no appreciable difference in the picture.

It's time to try replacing the Synchro Guide can. Fortunately, I know where I can source a 630 chassis to get the necessary part.

I've been back tracking your story on this TV. Wish I had come across it earlier. Lot of twists and turns! It occurs to me that the reason the width control doesn't have much effect is that the horizontal frequency is off so much. The reactance at that frequency isn't correct. So I would get the frequency right first then see to the width problem. Which resistor was it that was connected to the width coil?

This is an excellent time to practice with your new oscilloscope. There are books on using them, including one or more I found online (Oscilloscope Fundamentals from Tektronix is one). It should not be hard to connect it to see the signal in your horizontal oscillator, then check its frequency by matching the number of pulses on the scope screen to the scope's horizontal sweep setting (such as 100 microseconds (or 0.1 milliseconds) per division, the squares on the screen each being a "division").

If I have it right, a 15.75 kHz pulse is 63 microseconds, so you should see about three of them per every two divisions on a scope set for 100 uS/div or 0.1 mS/div, and adjusting the horizontal frequency would change the width of the pulses on the screen (and therefore, the number of pulses per division). This is just one example of a scope setup.

You're 100% right, and Notimetolooz, I'm sorry that I didn't respond to your question, honestly I just noticed it :)

I'll pick up on the 730 after ETF....for now it's buttoned up and has a nice coat of Pledge on it :) . When I get back on it, this thread shall continue :D

You don't want to use pledge on any furniture you want future generations to be capable of refinishing. It contains silicon which sinks into the wood and creates fish eyes in any new lacquer finish applied even after a strip and sand. The only finish that is immune is poly, and that stuff is sort of permanent once applied (which is why many restorers refuse to use poly).

Well it really doesn't *need* refinishing. The flash of course brings out every last imperfection and now that I've taken the pic I'm gonna go grab the Howard's and do a little touch up. Man, look at the dust on the moldings, I'm slipping!! :eek: ;)

I have a thick piece of glass on top which protects the top from anything I happen to plop there :)

I stopped using pledge when I heard of the silicon issue because I don't want future owners of my stuff to not be able to refinish it properly. If you switch to old fashioned furniture wax or citrus oil furniture cleaner you get the same type of clean/shine without annoying any future wood workers that have to deal with the set for the remainder of it's existence.

Yeah, I figured you must have gotten busy on other things. I was getting into it, even downloaded the Sams from the Early TV Museum website. I noticed there isn't any waveforms on that Sams. See you at the conference.
I expect to be there all day Saturday then Sunday morning. I'm staying with relatives in Ohio. My first time there! :thmbsp:
Another Tim

Remember this set? Yep, I still have it. Here's where it's at currently.

Replaced the Synchro-Lock, and it was working for about 10 minutes. All of a sudden, the picture shut off and the 6BG6 started hotplating. This was last winter.

Since I've replaced all of the obvious stuff, and gone far and above beyond that, this week I decided to stick in a new fly to see if that would cure the issue, since I had one here (was suggested by someone that I try that). Nothing.

After over two years, my disgust level with this set is high. I don't know what voltages are currently on anything because of that. If I can't fix this thing soon, it will go on Craigslist to be made into a dog bed and I really won't care :)

That said, please give me some advice on this thing. I'm at my wit's end.