Total posts : 45366
The TIP31 operates hot and it may have caused a problem with the solder connections on the printed circuit board. Carefully check the connections. From your description the problem is most likely in the LM358 and TIP31 part of the circuit and not in the frequency generating part of the circuit
If you can measure some voltages and post them here it could help. Measure the voltages to ground at the three terminals of R23.
Measure the voltages to ground at all pins of the LM358 and post them here. I might be able to tell from these measurements where to look further for the problem.