1. Test the horn, earphone, and dynamic microphone: use R×1Ω file, one of the pens is connected to one end, and the other pen touches the other end. When normal, it will emit a “beep†sound. If it doesn't ring, the coil is broken. If the sound is small and sharp, there is a problem with the rubbing circle.
2, measuring capacitance: use the resistance file, according to the capacity of the capacitor to select the appropriate range, and pay attention to the measurement of the electrolytic capacitor black pen to the capacitor positive. 1. Estimate the size of the microwave-level capacitor capacity: It can be judged according to the maximum amplitude of the pointer swing by experience or by referring to the standard capacitance of the same capacity. The capacitors to be referenced do not have to have the same withstand voltage values, as long as the capacities are the same. For example, it is estimated that a 100μF/250V capacitor can be referenced by a 100μF/25V capacitor, and as long as their pointer swings to the same maximum amplitude, the capacity can be determined. 2, estimate the size of the skin-level capacitor capacity: use R × 10kΩ file, but can only measure more than 1000pF capacitor. For a 1000pF or slightly larger capacitor, as long as the hands are slightly swung, the capacity is considered sufficient. 3. Measure whether the capacitor leaks: For a capacitor of more than one thousand microfarads, it can be quickly charged with R×10Ω file, and the capacitance capacity is initially estimated, then changed to R×1kΩ file and continue to measure for a while, then the pointer is not It should be returned, but should be parked at or very close to the place, otherwise there will be leakage. For some timing or oscillating capacitors below tens of microfarads (such as the oscillating capacitor of color TV switching power supply), the leakage characteristics are very high, as long as there is a slight leakage, it can not be used. At this time, after the R×1kΩ gear is charged, Then continue to use R × 10kΩ file to continue measurement, the same needle should stop at the ∞ and should not return.
3. In the road test diode, triode, and voltage regulator, it is good or bad: because in the actual circuit, the bias resistance of the triode or the peripheral resistance of the diode and the voltage regulator are generally large, mostly in the hundreds of thousands of ohms or more. , we can use the multimeter's R × 10 Ω or R × 1 Ω file to measure the quality of the PN junction in the road. When measuring the road, the PN junction measured by R×10Ω should have obvious positive and negative characteristics (if the difference between the forward and reverse resistance is not obvious, it can be measured by R×1Ω), and the general forward resistance is in R. When the ×10Ω is measured, the hands should be indicated at about 200Ω. When the R×1Ω is measured, the hands should be indicated at 30Ω (may vary slightly depending on the phenotype). If the measured value of the forward resistance is too large or the reverse resistance is too small, it indicates that there is a problem with this PN junction, and this tube is also problematic. This method is particularly effective for maintenance, can find the bad tube very quickly, and can even measure the tube that has not completely broken but the characteristics are deteriorated. For example, when you measure a PN junction with a small resistance value, the forward resistance is too large. If you solder it down and use the commonly used R×1kΩ file, it may still be normal. In fact, the characteristics of this tube have deteriorated. Not working or unstable.
4. Measuring resistance: It is important to select the range. When the pointer indicates 1/3~2/3 full scale, the measurement accuracy is the highest and the reading is the most accurate. It should be noted that when measuring the large resistance value of the ohms level with the R×10k resistance file, the fingers should not be pinched at both ends of the resistor, so that the human body resistance will make the measurement result smaller.
5, measuring the voltage regulator diode: the voltage regulator value of the regulator tube we usually use is generally greater than 1.5V, and the resistance file below the R × 1k of the pointer table is powered by the 1.5V battery in the meter, so The resistance voltage measuring tube below R×1k is like a measuring diode, and has complete unidirectional conductivity. However, the R×10k file of the pointer table is powered by a 9V or 15V battery. When the voltage regulator with a voltage regulation value less than 9V or 15V is measured with R×10k, the reverse resistance value will not be awkward, but there is a certain Resistance, but this resistance is still much higher than the forward resistance of the Zener. In this way, we can initially estimate the quality of the Zener tube. However, a good voltage regulator tube must have an accurate voltage regulation value. How can this voltage regulator value be estimated under amateur conditions? It's not difficult, just go find a pointer table and you're done. The method is: first place a watch in the R×10k file, and the black and red test pens are respectively connected to the cathode and the anode of the Zener tube, at this time, the actual working state of the Zener tube is simulated, and another table is placed. The voltage file V×10V or V×50V (according to the voltage regulation value), the red and black test pens are respectively connected to the black and red test pens of the watch, and the measured voltage value is basically this. The voltage regulation value of the Zener diode. Say "basically" because the bias current of the first watch to the Zener diode is slightly smaller than the bias current during normal use, so the measured voltage will be slightly larger, but the difference is not much difference. . This method can only estimate the voltage regulator whose voltage regulation value is lower than the voltage of the high voltage battery of the pointer meter. If the voltage regulator voltage is too high, it can only be measured by the external power supply. (It seems that when we use the pointer meter, the high voltage battery voltage is 15V, which is more suitable than 9V.)
6. Measuring triode: Usually we need to use R×1kΩ file, whether it is NPN tube or PNP tube, no matter it is low power, medium power, high power tube, it should be the same as the diode. Electrical, the reverse resistance is infinite, and its forward resistance is about 10K. In order to further estimate the quality of the pipe, if necessary, the resistance gear position should be changed for multiple measurements. The method is: set R × 10 Ω to measure the PN junction forward conduction resistance is about 200 Ω; set R × 1 Ω The positive conduction resistance of the PN junction is about 30Ω. (The above is the data measured by the 47-type meter. The other models have different outlines. You can test a few good tubes and sum up them.) If the reading is too large. Too much, it can be concluded that the characteristics of the pipe are not good. The table can also be placed in R × 10kΩ and then tested, the tube with low withstand voltage (the voltage of the triode is above 30V), the reverse resistance of the cb junction should also be in the ∞, but the reverse resistance of the be junction There may be some, the hands will be slightly deflected (generally not more than 1/3 of the full scale, depending on the pressure resistance of the pipe). Similarly, when measuring the resistance between ec (for NPN tubes) or between ce (for PNP tubes) with R × 10 kΩ, the hands may be slightly deflected, but this does not mean that the tubes are bad. However, when measuring the resistance between ce or ec with R × 1kΩ or less, the indication of the meter should be infinite, otherwise the tube is problematic. It should be noted that the above measurements are for silicon tubes and not for tubes. But now the fistula is rarely seen. In addition, the "reverse" is actually different for the PN junction and the direction of the NPN tube and the PNP tube.
Most of the common triodes are plastic encapsulated. How to accurately determine which of the three pins of the triode is b, c, e? The b pole of the triode is easy to measure, but how to determine which is c and which is e? Three methods are recommended here: The first method: For the pointer meter with the triode hFE jack, first measure the b pole, then insert the triode into the jack at random (of course, the b pole can be inserted accurately) Take the hFE value, then turn the tube upside down and measure it again. The hFE value is measured once and the position of each pin is inserted correctly. The second method: for the table without the hFE measuring jack, or the tube is too large to be inserted into the jack, you can use this method: For the NPN tube, first measure the b pole (the tube is NPN or PNP and its b foot) It's easy to measure, isn't it?), put the watch in the R×1kΩ file, and connect the red pen to the hypothetical e-pole (note that the hand holding the red pen does not touch the pen tip or pin), the black pen is connected to the hypothetical c pole, while pinching the tip of the meter and the pin with your fingers, take the tube up, use your tongue to rub the b pole, see the pointer should have a certain deflection, if your pens are connected correctly, the pointer will deflect Larger, if the connection is not correct, the pointer deflection will be smaller, the difference is obvious. From this, the c and e poles of the tube can be determined. For the PNP tube, the black meter should be connected to the hypothetical e-pole (the hand should not touch the nib or the pin), the red meter pen should be connected to the hypothetical c-pole, and the finger tip and the pin should be pinched with the fingers, and then the tongue tip is used to b) Extremely, if the pens are connected correctly, the head pointer will be deflected relatively large. Of course, the meter should be exchanged twice during the measurement, and the final reading can be made after comparing the readings. This method is suitable for all shapes of triodes, which is convenient and practical. Depending on the deflection of the hands, it is also possible to estimate the magnification of the tube, which is of course empirical. The third method: first determine the NPN or PNP type of the tube and its b pole, then place the meter in the R×10kΩ file. For the NPN tube, the black meter pen is connected to the e pole, and the red meter pen is connected to the c pole, the needle may have a certain amount. Deflection, for the PNP tube, the black meter pen is connected to the c pole, and the red meter pen is connected to the e pole, the needle may have a certain deflection, and vice versa. This makes it possible to determine the c and e poles of the triode. However, for high pressure pipes, this method is not applicable.