RCA 630TS sound problems

[blue_lateral]

Originally Posted by Phil Nelson

Thanks, I'll play around with the marker output a little more. As I recall, it disappeared completely when I turned the sig gen output to minimum.

I am injecting the marker by connecting the signal generator output to the external marker input of the sweep generator. I suppose I could try connecting it independently.

Yes, the instructions did say to connect the sweep gen at the antenna. In other alignment procedures they specified other connection points. This section was called "retouching picture IF" and you did it after completing all the rest.

I tried connecting the sweep gen at the converter tube rather than the antenna, and the display was much the same.

It should be. You should be able to move the marker right and left by varying the marker frequency. If you inject at the antenna terminals, at broadcast frequency, you can also move the marker right and left with the fine tuning.

As far as I know it is necessary to get the conversion process out of the way so you can believe *where* on the curve your marker is. For example on the color set I am working on, you bias the tuner off, and inject at IF frequency at the mixer grid. The mixer is acting as a simple amplifier. You inject at the grid, rather than the plate, because the mixer plate circuit is one of the ones you are trying to tune, and you dont want to detune it by hanging something on it.

Think of an old radio with a 455kc IF. You could peak up the IF's while listening to a station, and it would work, but you wouldnt know that you were *exactly* on 455kc. If you needed to be exactly on 455kc, you would have to inject a signal on exactly 455kc after the converter and align the IF transformers to that.

Originally Posted by Phil Nelson

I don't have much experience using an oscilloscope, so I don't have loads of confidence that what I'm seeing is meaningful. Maybe I should set this project aside and practice viewing waveforms on one of my other restored TVs.

I'm not by any means an alignment expert, but I have done it before, and your curves look meaningful to me. One thing, you should be able to turn the sweep generator output up and down a little without changing the *shape* of the curve. If the output is too high, the IF will clip, and clipping produces a flat-topped curve that looks like a good curve. The AGC probably also needs to be disabled, so it doesnt try to "correct" the gain.

Have fun

John