I am trying to debug 50 boards that are implementing the LM331 as a voltage to frequency converter. My desired frequency is 3.9 kHz. On 10 of the boards the frequency is within +/- 2kHz which is okay for my application. However on the rest of the boards the frequency is more like from 7.2 kHz to 8.4kHz. And i havent founf any difference regarding to the voltages on the pins.. The voltages at all the other pins are the same. All my resistors are 1% and the caps are 5%. I've tried changing Rt, Ct and the LM331 but the result is still the same. My schematic is shown with a 3.6V input. Any suggestions as to why this is? Disregard the notes on the schematic. Also any other solution other than that of putting POT. Thank You