Horiz osc question

[7"estatdef]

As I am working on this KCS-47 I'm have trouble getting the horizontal osc on the proper frequency. I locks nicely on twice and three times the frequency. So I got the bright idea to hookup a counter to the control grid of the 6BG6 just to see where it's at but I can't seem to get it to get a constance reading in that it won't settle down in one freqency. Is does the osc generate alot harmonics so the counter can't figure out which freq to lock onto?
Terry

[trinescope]

The waveform at the horizontal output tube on these sets is essentially a sawtooth; there should be no problem getting a stable reading (unless you're overloading the freq. counter as it's about 40V P-P). Assuming you have already replaced the wax-covered and molded striped capacitors, you may have a resistor (or several) that have drifted out of spec. One more thing: Make sure to use a plastic film capacitor across the synchroguide coil (the one you use to adjust horizontal frequency). I found out the hard way that using a ceramic causes serious frequency drift.

[Don Lindsly]

The synchroguide circuit is basically a Hartley ocsilolator followed by a wave shaping coil. The oscillator is tuned to the horizontal scan frequency; 15,750. The wave shaping coil is tuned to twice the frequency.

One way to get the circuit close is to short the wave shaping coil with a clip lead. Center the horizontal hold control and tune the oscillator coil for a normal picture. Then remove the short and tune the wave shaping coil for a stable picture, without touching any of the previous adjustments. Once you get the circuit tuned, you can fine tune it by connecting a scope in series with a resistor, 27 K or so, to the point on the oscillator coil where the resistor and capacitor meet. Then adjust the wave shape to where the peak is equal to, or about 10% higher than the hump for best stability. That will not require much adjustment.

If you are not sure which end of the coil is the oscillator, it will be the only one that has effect when the wave shaping coil is shorted.

If that does not work, it will point to the source of the trouble.

Don

[Einar72]

When I got my first KCS-47 way back when, it had a quadruple-image problem. There is a molded capacitor across two terminals of the horizontal oscillator coil can, it's what caused me to re-cap my chassis! The adjustments described above will not help if this cap is bad. I've even seen this problem covered in a (legendary) Jack Darr TV-repair book! It's a .01, I think. It's the same color and about half the length of a piece of a Bit O' Honey candy. Molded from what, I don't know, but it leaked down to the kilohm stratum, especially when I held a flame nearby. This was in 1985, when it was barely 35 years old! Just put in a nice, trusty Orange Drop rated @400-600V and tweak the ringing/stabilizer/sine wave coil (whatever it's called in your service literature). Worked great for me!

[trinescope]

That's the capacitor I was talking about where I used a ceramic cap with poor results. I usually see one of those stripey paper caps there (it is .01µF, BTW).

On a side note, and I could be wrong, but I don't think that the horizontal output/flyback circuits would work very well if at all at 2 or 3 times the normal frequency.

Also, any capacitor that says "micamold" on it is not so; it is actually a paper cap that will need replacement.

[wa2ise]

If it looks like the horiz is at twice or 3 times what it should be, it's probably just got itself into a ratio of 3 to 2 or 4 to 3.