Yes, the chip is an LM3900 quad Norton amplifier.
I checked the waveforms: Pin 4 - triangle, Pin 5 - square, anode of D5 - sine. So those seem correct. I think I was probing a wrong pin yesterday

. What I called pin 3 should have been pin 5. So the voltages on
pin 5 are 7.2-7.6v (oscillating) with the speed control at min, and 0.5v (steady) with the speed control at max.
Here are the voltages on the input pins:
Pin
1 0.46v
2 0.14-0.19v (Speed control min-max)
3 0.13-0.16v (Speed control min-max)
6 0.14v
8 0.54v
11 0.43v
12 0.39v
13 0.40v
I could re-check continuity in the LFO, but other than that the LFO seems to be working OK when the speed control is set to a low speed. So what could fail and affect the speed of the oscillator? C11, C12, Q2, or the chip. When operating correctly, the speed control should vary from 1 cycle every 3 seconds to 15 cycles per second.