Complete Electronics Self-Teaching Guide with Projects

Oscillator Troubleshooting Checklist

If an oscillator does not work, most often the trouble is with the feedback connections. A little experimenting (as outlined in steps 2 through 6 of the following checklist) should produce the right results. This is especially true when you use an unknown coil that may have several taps or windings. However, you should try each of the following steps if you have trouble.

1. Ensure that C_B, C_C, and C_E are all large enough to have a reactance value less than 160 ohms. Ensure that C_E is less than one-tenth of R_E.

2. Check the C₁/C₂ ratio. It should be between 3:1 and 10:1.

3. Swap out C₁ and C₂. They may be connected to the wrong end of the LC circuit.

4. Check that you made the feedback connection to and from the correct place.

5. Check both ends of the LC circuit to see that they are connected to the correct place.

6. Check the DC voltage level of the collector, base, and emitter.

7. Check the capacitor values of the LC circuit. If necessary, try some other values until the circuit oscillates.

8. If none of the previous actions produce oscillations, check to see if any of the components are defective. The coil may be opened or shorted. The capacitor may be shorted. The transistor may be dead, or its β may be too low. Check the circuit wiring carefully.

In most cases, one or more of these steps produces oscillations.

When an oscillator works, it may still have one or two main faults, including the following:

• Distorted output waveform ...