2-22
Figure 2-17.—Testing a Zener diode.
Figure 2-18.—Zener diode characteristic curve.
TESTING TRANSISTORS
Most transistorized equipments use printed circuit boards on which components are neatly arranged.
This arrangement makes the transistors and other components easy to reach while you are troubleshooting
and servicing the equipment. While investigating with test probes, however, you must be careful to
prevent damage to the printed wiring.
One of the outstanding advantages of transistors is their reliability. Tube failures account for over 90
percent of the failures in electron-tube equipments. Transistors, however, are long lived. This factor,
among others, decreases maintenance required to keep transistorized equipment operating. The techniques
used in testing transistorized equipment are similar to those for maintaining electron-tube circuits.
Basically, these techniques include several checks and inspections.
Power Supply Checks
When using test equipment to localize a trouble, you should check the power supply to see that its
output voltages are present and of the correct values. Improper power supply voltages can cause odd
effects. You will prevent many headaches by checking the power supply first.
