Originally posted by Jerry
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I've seem some crazy waveforms at u101b pin 1, but yours looks particularly unfamiliar - can you confirm you are measuring what I think, which is: the output pin of LF353 that connects to the DISC pot?
I think maybe you are scoping pin 2, the inverting input of U101b (LF353). The output is more revealing as to how it affects the sync pulse.
Also, to really see what is driving the sync pulse, try scoping U102a (LM393) pin 2, the inverting input of the comparator connected by resistor to DISC pot wiper. Then as you turn the DISC pot, you can really see why the phase shifts where it does. Maybe that is what you meant to do anyway.
Regarding the "double" sync pulse that happens at one extreme of the DISC pot -- I had originally thought it was due to all the "ringing" in the LF353 output. Today I checked (with dfbowers' TGSL) and noticed that the double pulse happens when the comparator is driven purely by the TX oscillator signal. My guess it is due to the oscillator voltage going beyond the "rails" of the comparator and causing the glitch when the DISC pot mostly selects the oscillator signal.
Regards,
-SB
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