I am powering this circuit with two 9V batteries. I'm using the values R1=R2=10KΩ, C1=C2=100nF, R3 = 1KΩ, R4 = 470Ω. The oscilloscope just shows a flat line, no matter what values I try. I also tried hooking up a 8 Ohm speaker to V_OUT and circuit ground, since the oscillation amplitude and expected frequency are sufficient to make the wave audible. But there is only static.
I have tried a number of things to troubleshoot the circuit:
Using different resistor values, consistent with the circuit requirements.
Built a working comparator circuit using the op amp chip to ensure that the chip is good.
Checked all voltages.