VHF Tuner Alignment: where is the overall oscillator adjustment?

[Yamamaya42]

The only experience I have had so far with IF alignment is on my Arvin TV, and that took 4 passes of adjust for Max/Min levels with an RF generator and volt meter to get NEAR OK!

[old_tv_nut]

I keep forgetting to add that all this analysis of what might be wrong has been based on all the bypass caps in the chroma and oscillator circuits being good. If one is open, that might mess up things.

[LukeSimon]

I have now reached the stage of learning where sweeping RF, IF, and chroma is fun. Possibly because I now know what I am doing and I am getting good results.

After digging through 1960s and 1970s issues of “Electronic Technician” that are available as free scanned PDFs on worldradiohistory.com, I learned that the typical artist renditions of the alignment bode plots are not accurate in their shape. There are actually two sphapes that an alignment bode plot should have. It depends on the TV model: either a flat top bode plot or a “haystack”. The authors in Electronic Technician say that you will know which shape your TV uses because one will fall into place more naturally whereas the other shape will fight you as you try to align it. For the T933, the bode plot is the “haystack” type.



Here is a before vs after alignment. Note the improved sharpness and decreased color smearing.



Colored text in the upper left corner is a real stress test due to dynamic convergence, focus, degaussing, and RF/IF/chroma alignment. I wish I had a before picture of “red” at the very start of this project before I fixed the focus and dynamic convergence problems. I am very happy with this restoration progress.

I will be watching old Christmas movies this year, on this Magnavox.

[old_tv_nut]

Great so far, but the off-center tint control is still a problem.

[LukeSimon]

Originally Posted by old_tv_nut

Great so far, but the off-center tint control is still a problem.

I haven’t fixed the root cause, and I am sure that when I do fix it, I will be able to get an even better picture due to being able to use a better chroma bandpass bode curve than I am using now. However, these amazing analog TVs are so malleable and organic that they can handle significant component drift and failure.