Multimeter to determine the good and bad composite tube method
Use the multimeter to identify the good and bad composite tube. The multimeter will be placed in the R xlkΩ file, the red meter stick take over the gate of the tube G, the black meter stick connected to the source pole S. This time the head pointer should not move, at least should be greater than 500kΩ or more, then the gate is good. If less than 500KΩ, the tube gate leakage, not good. If the resistance value is close to zero, then the gate has broken down, the tube under test has been completely damaged.
After the above measurements, such as the gate resistance is good, then the multimeter two rods for the alignment, that is, the black meter stick connected to the gate G, the red meter stick connected to the source S. If the resistance value measured at this time and the meter stick before the alignment of the same, that is, the measured tube is not set up inside the gate to protect the diode, if the value of resistance is less than 10k Ω (generally in the 2k Ω or so), that the tube has been set up inside the gate to protect the diode.
After connecting the line, close the switch K. This time, the normally closed contacts of the button switch will be shorted to the gate, source, that is, VGS = OV, the tube does not conduct, the line of light-emitting diodes do not light. Then press the push-button switch, this time the normally open contacts will gate and emitter short circuit, VGS is negative, the tube conducts, there is current flow through the light-emitting diode, light-emitting diode light. The 300Ω resistor in the figure is the current limiting resistor of the light-emitting diode. After measurement, to meet the above requirements, indicating that the measured high impedance composite tube function is normal.
If the light-emitting diode lights up after closing the switch K, it means that the source-emitter is penetrated or the source-drain of the MOS tube is penetrated and the tube is damaged. Conversely, if the light-emitting diode still does not light up after pressing the push-button switch; it means that the tube gate may be worn, or the gate leakage is too large and the gate control is lost, and the tube cannot be used.
Digital multimeter resistance file principle maintenance method
① Check whether the switch is poor contact. This is a common cause of resistance failure.
② Check whether the thermistor is open-circuit failure or resistance value becomes large. Thermistor is connected in series in the resistance file before the standard resistance protection device, when its open-circuit failure, will make the whole resistance file can not be measured: when the resistance value becomes very large, the lesser cause great measurement error, the heavier will make the resistance file failure.
③Check whether the standard resistor is open-circuit failure or resistance value becomes large. Standard resistors are connected in series to form a resistance measurement circuit components, once a resistance range of the standard resistor is open-circuit state, not only to make the range failure, but also with the relevant range will also be implicated. Check according to the specific performance of the fault analysis and judgement.
④Check whether the capacitor (0.1 u F) connected in parallel between the c-e poles of the overvoltage protection transistor is short-circuited or seriously leaking.
⑤ Check whether the resistor in series with the reference voltage output is broken or desoldered.
