TESTING SEMICONDUCTOR DEVICES

2-19 Figure 2-14.—Spectrum analyzer pattern. Q-10. What device sweeps a band of frequencies to determine frequencies and amplitudes of each frequency component? The spectrum analyzer is used to examine the frequency spectrum of radar transmissions, local oscillators, test sets, and other equipment operating within its frequency range. Proper interpretation of the displayed frequency spectrum enables you to determine the degree of efficiency of the equipment under test. With experience, you will be able to determine definite areas of malfunctioning components within equipment. In any event, successful spectrum analysis depends on the proper operation of a spectrum analyzer and your ability to correctly interpret the displayed frequencies. Later, in chapter 6, we will discuss the various controls, indicators, and connectors contained on the spectrum analyzer. TESTING SEMICONDUCTOR DEVICES Because of the reliability of semiconductor devices, servicing techniques developed for transistorized equipment differ from those normally used for electron-tube circuits. Electron tubes are usually considered to be the circuit component most susceptible to failure and are normally the first components to be tested. Transistors, however, are capable of operating in excess of 30,000 hours at maximum rating without failure. They are often soldered in the circuit in much the same manner as resistors and capacitors. Therefore, they are NOT so quickly removed for testing as tubes. Substitution of a semiconductor diode or transistor known to be in good condition is one method of determining the quality of a questionable semiconductor device. This method should be used only after you have made voltage and resistance measurements. This ensures the circuit has no defect that might