- Digital tube damage discrimination detection
First, set the multimeter to the R×10k or R×100k position, then connect the red probe to the “ground” terminal of the digital tube (taking the common cathode digital tube as an example), and connect the black probe to the other terminals of the digital tube in sequence. All seven segments should light up separately, otherwise it indicates that the digital tube is damaged.
- Distinguish the electrodes of junction field-effect transistors
Place the multimeter in the R×1k range, use a black probe to contact the pin assumed to be gate G, and then use a red probe to contact the other two pins separately. If the resistance values are relatively small (5~10Ω), exchange the red and black probes and measure again.
If the resistance values are all high (∞), it indicates that they are all reverse resistors (PN junction reverse), belonging to N-channel transistors, and the pin in contact with the black probe is the gate G, indicating that the original assumption was correct.
If the resistance values measured again are all very small, it indicates that it is a forward resistance and belongs to the P-channel field-effect transistor. The black probe is also connected to the gate G. If the above situation does not occur, the red and black probes can be replaced and tested according to the above method until the gate is determined.
The source and drain of a typical junction field-effect transistor are symmetrical during manufacturing. Therefore, once the gate G is determined, it is not necessary to distinguish between the source S and drain D, as these two electrodes can be used interchangeably. The resistance between the source and drain is several thousand ohms.
