Semiconductor Tester

This project is a series-type ohmmeter designed specifically to check Diode and Transistor junctions for rectifier action. This is the same type circuit used in many VOM's (volt-ohm-milliamp meters) to measure resistance, but this project includes this particular circuit and test procedures specifically to test rectifying junctions.

The test procedure is as follows:

1. Connect the test Probes to the device (Diode, Transistor B-E or B-C junction) with the polarity which allows the Control to be adjusted for a full-scale Meter reading on the blue Meter scale. Adjust for this level and leave the Control at that setting.

2. Reverse the test Probes and observe the Meter reading. The Meter readings should be interpreted as follows:

a. If the Meter reading is still 10 (full scale) the device has no rectifier properties or is shorted.

b. If the Meter reading is above about 1.0 on the blue scale (but below 10) the device is a poor rectifier junction because of excessive leakage. (Or something is shunted across the device. Make sure nothing is connected in parallel with the junction being tested.)

c. With a Meter reading below about 1.0 for germanium (Ge), rectifiers are good.

d. Meter readings below about 0.5 (the first small Meter scale marking) for germanium Transistor B-E and B-C junctions, indicate they are good.

e. Meter readings of zero (or very close to it), for all silicon (Si) rectifiers and silicon Transistor B-E and B-C junctions, indicate they are good.

It would be a good idea to check all Diodes and Transistor junctions in this kit and record the results below. This way, later on you can check and compare when one of these devices is suspected of being defective.

You may want to use your knowledge gained from project Diode Action or Diode Switch in Diode Section to include a polarity reversing switch with this circuit. If you can do this you are progressing wonderfully in your training in electronics. Good luck! .