I’ve had the same issue and not much more success finding resources than you seem to have had. I noticed some discolouration on the SA571N and it looks like the clock signal generated by this thing has given up the ghost! Apparently you SHOULD see a fluctuating voltage here, not less than 70% of what is coming out of the voltage regulator (around 15vdc). I have a static 6.3V at pin 6 so I’ve ordered a new SA571N with finger crossed!!! Wish me luck!