Detection skills of main components in frequency inverter maintenance

I. Detection methods and experience of fixed resistors

Connect two test leads (regardless of positive and negative) to the two ends of the resistor to measure the actual resistance value. In order to improve the measurement accuracy, the range should be selected according to the nominal value of the measured resistor. Due to the nonlinear relationship of the ohm scale, its middle section is more fine, so the pointer indication value should be as close to the middle of the scale as possible, that is, within the 20% to 80% arc range of the full scale, so as to make the measurement more accurate. According to the different resistance error levels. The reading is allowed to have an error of ±5%, ±10% or ±20% between the nominal resistance value. If it does not match and exceeds the error range, it means that the resistance value has changed.

II. Detection methods and experience of fixed capacitors

A. Detection of small capacitors below 10pF Because the capacity of fixed capacitors below 10pF is too small, using a multimeter to measure can only qualitatively check whether it has leakage, internal short circuit or breakdown. When measuring, you can use the multimeter R×10k block, and use two test pens to connect the two pins of the capacitor at will. The resistance should be infinite. If the measured resistance (the pointer swings to the right) is zero, it means that the capacitor is leaking or damaged or internally broken down.

B. Detect whether the 10pF~1000μF fixed capacitor has charging phenomenon, and then judge whether it is good or bad. The multimeter uses the R×1k block. The β values of the two transistors are both above 100, and the penetration current should be slightly higher. Silicon transistors such as 3DG6 can be used to form a composite tube. The red and black test pens of the multimeter are connected to the emitter e and collector c of the composite tube respectively. Due to the amplification effect of the composite transistor, the charging and discharging process of the measured capacitor is amplified, so that the swing amplitude of the multimeter pointer is increased, which is convenient for observation. It should be noted that: during the test operation, especially when measuring a capacitor with a smaller capacity, it is necessary to repeatedly switch the pins of the measured capacitor to contact points A and B, so that the swing of the multimeter pointer can be clearly seen.

C. For fixed capacitors above 1000μF, the R×10k range of the multimeter can be used to directly test whether the capacitor has a charging process and whether there is an internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.

III. Detection and experience of crystal triodes

Crystal triodes mainly play an amplifying role, so how to judge the amplification ability of triodes? The method is: adjust the multimeter to R×100 or R×1K. When measuring NPN type tubes, the positive meter pen is connected to the emitter and the negative meter pen is connected to the collector. The measured resistance should generally be more than several thousand ohms; then connect a 100 kilo-ohm resistor in series between the base and the collector. At this time, the resistance measured by the multimeter should be significantly reduced. The greater the change, the stronger the amplification ability of the triode. If the change is small or there is no change at all, it means that the triode has no amplification ability or the amplification ability is very weak.