Weird issue with an RCA 730TV2

[Kamakiri]

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.

[Username1]

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....

.

[Kamakiri]

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".

[Findm-Keepm]

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?

[Username1]

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.

.

[Kamakiri]

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

[Kamakiri]

Originally Posted by Findm-Keepm

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?

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

[Notimetolooz]

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.

[Kamakiri]

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.

[Notimetolooz]

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?

[ChrisW6ATV]

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.

[Kamakiri]

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

[Electronic M]

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).

[Kamakiri]

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!!

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

[Electronic M]

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.