Textile equipment circuit board repair tips

With the increasing automation of textile equipment, inverters and PLC circuit boards have become indispensable main components of textile equipment. However, as the equipment has been in operation for many years, circuit board failures have occurred, which has led to an increase in maintenance costs for enterprises. Through years of work practice, I have summarized some small experiences and skills in circuit board maintenance and component testing, which are now shared with peers for communication and discussion.

(1) Maintenance of the switching power supply circuit board.

After power-on, the fuse is damaged by the rectifier bridge, the switch power supply integrated block (UC3842) or the power supply filter capacitor. After the switch power supply board is energized, the voltage across the power supply filter capacitor is measured. After the power is turned off, the voltage across the power supply filter capacitor cannot be very high. The short time disappears, which proves that the starting resistance of the switch tube is unreachable; the switching power supply board has no output, and the electrolytic capacitor part on the circuit board can be replaced, which can get twice the result with half the effort; the output voltage of the switching power supply board is unstable, and it is the switching power supply board. Poor contact of the upper adjustable resistor or poor performance or damage of the voltage regulator block (T431) optocoupler; the switch tube on the switch power supply board is often damaged, which may be the high frequency sharp pulse circuit capacitance or resistance of the switch tube; When the device is powered on in the cold state, the display digits flashes and cannot be operated. After a few minutes, it can be used normally, and it will gradually become longer and longer. Most of the reasons are the switching power supply and the leakage of the two side electrolytic capacitors. The capacitance of the capacitor is reduced; the resistance of the on-line measurement resistor should be less than or equal to the nominal resistance of the resistor, otherwise it is not normal.

(2) The failure of the carding dust filter electrical control PLC.

If the power indicator is not lit, no output, after online detection, the fuse 2A is blown, and the breakdown of 1N4007 and 0.47VF/400 electrolytic capacitors is damaged. After replacing the insurance and 1N4007, if there is no 0.47VF/400 electrolytic capacitor, two 1VF and 400V electrolytic capacitors can be replaced in series, so that the PLC works normally and the effect is good.

(3) CPU test.

The main conditions for CPU operation are 3 elements: the power supply circuit is powered normally; reset, use the multimeter DC voltage file to test the reset point, in the on/off state, there is no voltage instantaneously, there is obvious voltage fluctuation as normal; oscillating circuit, most transistors Oscillator, one foot high voltage (2V or more), the other pin voltage is low (zero volts), colliding with the transistor oscillator two legs, if the test is high voltage foot, the voltage has obvious change, indicating that the CPU internal clock oscillation circuit works normally. .