Troubleshooting Techniques

1. Symptom: Comparator circuit doesn’t seem to work Symptom: Schmitt trigger circuit doesn’t seem to work • Temporarily connect jumper J1 or J2, to force the comparator from its current state to the opposite rail voltage. • If you can’t force the comparator into the alternate state, check the power-supply voltages and the voltages in the reference-voltage circuit. Another possibility is that the IC is bad. • Verify that the reference voltage is correct. • If the reference voltage is okay, and if it is possible to force the comparator into the alternate state, then the comparator is okay, and the likely problem is with the input signal. • Temporarily connect jumper J1 or J2, to force the comparator from its current state to the opposite rail voltage. • If you can’t force the comparator into the alternate state, check the power-supply voltages and the components in the positive-feedback circuit. Alternatively, the IC may be bad. • If the positive feedback circuit is okay, and it is possible to force the comparator into the alternate state, the comparator is okay and the likely problem is with the input signal. Troubleshooting Op-Amps (Cont’d) Troubleshooting Techniques Internal Failures in Comparator circuits External Component Failures in Comparator circuits R1 and R2 set the UTP and LTP for the hysteresis comparator. When the R2 open, all of the output voltage is fed back to the noninverting input. Since the input voltage will never exceed the output, the device will remain in one of its saturated states. When R1 open, this leaves the noninverting input near ground potential and causes the circuit to operate as a zero-level detector. 0 V Quick Check for a Comparator with Hysteresis Quick Check for a Comparator