Weird issue with an RCA 730TV2

[Zenith26kc20]

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?

[Kamakiri]

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.......

[jr_tech]

Originally Posted by Kamakiri

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

[Phil Nelson]

Originally Posted by Kamakiri

RCA WO-33A. However, as of yet I don't have a clue how to use it

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.



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

[Kamakiri]

Originally Posted by jr_tech

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

I'd love you!

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

[jr_tech]

Originally Posted by Kamakiri

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

[Electronic M]

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...

[Zenith26kc20]

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!

[Kamakiri]

Originally Posted by jr_tech

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

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.

[dtvmcdonald]

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.

[Kamakiri]

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.....

[timmy]

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.

[Electronic M]

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.

[dtvmcdonald]

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.

[Kamakiri]

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 . 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?