If you have a multimeter check the voltage at U2 pin 7. If close to either 0 or 5 that suggests the oscillator is not running.
I did check it in two cases:
1. with external power ON: pin 8: 3.2V, pin 7:0.24V, pin 6:3.37V, pin 5: 0V, pin1:5.09V, pin 2:0.31V, pin 3:0.43V, p4: 0V
2. without external power: pin 8: 3.2V, pin 7: 0V, pin 6: 0V, pin 5: 0V, pin1: 0V, pin 2:0.14V, pin 3:0.29V, p4: 0V