I suspected CL1 because that is where the scope image starts swinging around. I swapped CL1's and the issue was not resolved...moving on.
This is where the voice in your head should tell you "
Sir, put the soldering iron down and back away from the instrument!"
At C10 i don't get a waveform on either machine, but just a jumbled up mess of a line that looks like noise. The image is swinging wildly at the C10 pin closest to S1. If you are referring to the "point to the right" being from an arial view of the component side, that would be this pin. I put my voltmeter on this point and it is all over the place (in mV).
Where does the negative lead of C10 go? I see a triangle with what appears to be a "1" inside of it.
What you should have at C10 is a relatively smooth, stable DC with a bit of ripple if your source is 60Hz. If that is going crazy, that might be your issue--but if you see the same thing on the other instrument, perhaps there is an issue with your measurements?
The symbol represents the guarded ground or common. That should tie in with nearby TP4 and that is where the ground lead of your oscilloscope should go. Is your AC source ground-referenced? If so, is the ground side connected to the COMMON input on the DMM? Is your scope DC-coupled? Once you are sure all that is good, check these points with your scope and a 1.5V
RMS input.
Q1 inputs pins 2 & 3, you should see a sine wave corresponding to the input but offset somewhat. These should be quite stable and smooth. The offset is the result of using CL1 and Q1 as the input buffer. If it is not steady, try to describe accurately in what way it is unsteady.
Q1 output pin 6, you should see the waveform I posted, again quite stable and smooth. If not, note how jumpy and irregular it is in terms of millivolts of deviance or instability.
R10/C9/CR5 junction, you can get this on the rear end of R10. What I see on mine is a pretty good sine wave with a lot of offset. It has a DC mean and an AC RMS value (set your scope to calculate those if you have that feature) that are both about 1.5V, same as the input.