Introduction to the technique of measuring transistors with a multimeter
Usually, we need to use the R × 1k Ω range. Whether it is an NPN transistor or a PNP transistor, whether it is a low-power, * * rate, high-power transistor, the be junction and cb junction should exhibit the same unidirectional conductivity as a diode, with infinite reverse resistance and a forward resistance of about 10K. To further estimate the quality of the tube characteristics, it is necessary to change the resistance level for multiple measurements. The method is to set the R × 10 Ω level and measure the PN junction positive conducting resistance, which is around 200 Ω; Set the R × 1 Ω range to measure the forward conducting resistance of the PN junction, which is around 30 Ω. (The above data is obtained from a 47 type meter, and other models have different readings. You can try testing several good tubes and summarize them to have a clear idea.) If the reading is too large, it can be concluded that the characteristics of the tube are not good. You can also place the meter at R × 10k Ω for testing. For tubes with lower withstand voltage (basically, the withstand voltage of a transistor is above 30V), the reverse resistance of its CB junction should also be ∞, but the reverse resistance of its BE junction may be slightly off center, and the pointer may deviate slightly (generally not exceeding 1/3 of the full range, depending on the withstand voltage of the tube). Similarly, when measuring the resistance between ec (for NPN tubes) or ce (for PNP tubes) using the R × 10k Ω range, the gauge needle may slightly deflect, but this does not mean that the tube is damaged. But when measuring the resistance between CE or EC in the range of R × 1k Ω or below, the gauge should indicate infinity, otherwise there is a problem with the tube. It should be noted that the above measurements are for silicon tubes and are not applicable to germanium tubes. However, germanium tubes are also rare now. In addition, the term "reverse" refers to the PN junction, and the direction of NPN and PNP transistors is actually different.
