Transistors refer to all single components based on semiconductor materials. Transistors have multiple functions such as detection, rectification, amplification, switching, voltage stabilization, signal modulation, etc. Transistors can be used for various digital and analog functions. On December 16, 1947, William Shockley, John Bardeen, and Walter Brattain successfully manufactured the first transistor at Bell Labs. Transistors are one of the most critical components of modern electrical appliances. The reason why transistors can be widely used is that they can be produced on a large scale at extremely low unit costs.

The transistors in circuits mainly include crystal diodes, crystal triodes, thyristors, and field-effect transistors, among which the most commonly used are transistors and diodes. How to correctly judge the quality of transistors is one of the key factors in learning maintenance.

Crystal diode: First of all, we need to know whether the diode is a silicon tube or a germanium tube. The forward voltage drop of a germanium tube is generally between 0.1 volts and 0.3 volts, while that of a silicon tube is generally between 0.6 volts and 0.7 volts. The measurement method is to use two multimeters to measure. When one multimeter measures its forward resistance, use the other multimeter to measure its tube voltage drop. Finally, the value of the tube pressure drop can be used to determine whether it is a germanium tube or a silicon tube. Silicon tubes can be measured using the R × 1K range of a multimeter, while germanium tubes can be measured using the R × 100 range. Generally speaking, the greater the difference between the forward and reverse resistance of the measured diode, the better. Generally, if the forward resistance is several hundred to several thousand ohms and the reverse resistance is several tens of thousands of ohms or more, it can be preliminarily concluded that this diode is good. At the same time, the positive and negative terminals of the diode can be determined. When the measured resistance value is several hundred ohms or several thousand ohms, it is the forward resistance of the diode. At this time, the negative probe is connected to the negative terminal, and the positive probe is connected to the positive terminal. Additionally, if the forward and reverse resistance is infinite, it indicates an internal disconnection; A diode with the same resistance in both forward and reverse directions is also problematic; A zero resistance in both directions indicates a short circuit.

Crystal transistor: The crystal transistor mainly functions as an amplifier. The method to measure the amplification capability of the transistor is to set the multimeter to R × 100 or R × 1K. When measuring an NPN transistor, connect the positive probe to the emitter and the negative probe to the collector. The measured resistance should generally be several thousand ohms or more; Then connect a 100 kiloohm resistor in series between the base and collector, and the resistance value measured by the multimeter should significantly decrease. The greater the change, the stronger the amplification ability of the transistor. If the change is small or there is no change at all, it indicates that the transistor has no amplification ability or weak amplification ability.