An example of fault analysis and maintenance of th

2022-08-24
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An example of fault analysis and maintenance of CM integrated tester

with the continuous emergence of communication products, accurate and comprehensive detection of them is more important. CMT integrated tester is one of the equipment for testing communication products, which is mainly used to detect the performance indicators of receivers and transmitters

2 fault phenomenon

after power on, the display is normal, the initialization is normal, and the output power is inaccurate in the test state of the receiver

3 analysis and maintenance

in CMT, the RF signal generated by the RF oscillator is connected to the signal input/output port of the CMT panel by its power output stage through a group of attenuators. The attenuator group consists of two 40dB, two 20dB, one 10dB and one 5dB fixed attenuators. The minimum resolution is 5dB. The magnitude between 0 and 5dB is generated by the electronic circuit of the RF oscillator output stage

select a power meter with appropriate range to test the output power half of CMT during maintenance. The test range is selected as 5dB step, full range test. Comparing and analyzing the test results with the set values, it is found that there are errors in the test points related to 20dB Fixed Attenuators: that is, the test points without 20dB fixed attenuators are normal; The test point using 20dB fixed attenuator is abnormal. It is preliminarily judged that the fault is from 20dB attenuator

test the output value between 0 and 5dB, the test value is consistent with the set value, and the result is normal. Therefore, the electronic circuit of RF oscillator output stage is normal

in order to further determine the cause of the fault, disconnect the connection between the RF oscillator output stage and the attenuator group, test the RF oscillator output stage with a power meter, and the test data is normal

through the above three tests, it is analyzed that the fault lies in the 20d16 of the attenuator group and the experimental software B fixed attenuator and its control circuit under the windows platform of the digital display electronic tensile testing machine in Chinese

use the method of adding control signal to make the switches KL ~ K7 of the control attenuator close in turn, and the measured attenuator accuracy is the same as the nominal value of the technical index, so as to judge that each fixed attenuator and its wire package are normal, and the problem lies in the control signal of the attenuator group switch

note: the wire package of attenuator group switches K1 ~ K7 is controlled by pulse signal. When the control pulse signal is generated by the change of the level of the control signal, the switching state of the attenuator changes, otherwise the switches K1 ~ K7 remain in the original state

the attenuator group switch is controlled by a serial input/parallel output shift register through power drivers D10 ~ D13. Under normal conditions, the corresponding output terminals of drivers D10 ~ D13 are low level, the attenuator is in the straight through state, and the attenuation of the attenuator group is 0dB. When the corresponding output terminals of drivers D10 ~ D13 are at high level, the attenuator is in working state. The attenuation of the attenuator group is the corresponding value

use a digital voltmeter to detect the voltage at each control point

set the oscillator output level in 10dB steps, and detect the corresponding output level of drivers D10 ~ D13 in turn. It is found that no matter what state the RF oscillator output level is set, the corresponding output of driver D13 remains at the low level. That is, V8 output high level. V8 is the output of CMT overvoltage protection (reverse power protection). Under the current state, CMT does not have the problem of overvoltage (reverse power) after testing, and the fault lies in the protection circuit

the signal channel of overvoltage protection in CMT is Z9 to obtain the sampling signal → z11/z12 capacitor → N1 comparator → D3 (pin6) trigger → V8, so as to control D13. Disconnect V6 and measure N5 (Pin1) with a digital voltmeter as +15v, normal. At present, the industry has adopted technologies such as modified asphalt, lignin preparation, polyolefin preparation, high-strength PANCF precursor, energy-saving processing energy and so on to reduce the carbon fiber production cost N1 (pin7) to +3v, which is abnormal. Under normal conditions, this point is about - 15V

disconnect V3 and V4 again, and N1 (Pin1) is measured to be +15v; N1 (pin7) is +3v, and both points should be about - 15V under normal conditions. Since there is no overvoltage (reverse power) phenomenon, try adjusting resistor R34 so that NL (pinl) is - 15V; N1 (pin7) is - 15V, reaching the normal state value

at this time, N1 (Pin2) is measured to be +2.8v; N1 (PIN3) is +2.2v, N1 (pin5) is - 2.8V; N1 (pin6) is - 2.1V

when adjusting R34, it should be noted that the voltage difference between the in-phase input end and the reverse input end of N1 is greater than 0.5V. If the voltage difference is less than 0.5V, the output state of N1 will be reversed

after the resistance R34 is adjusted, the detection D3 (pin6) is - 5V, D3 (Pin1) is +5v, and the V8 output is about 0.4V low level. The prosperity of the paper industry continues to decline. The paper mill can only play D13 with a card in short supply of raw materials. The corresponding output is high level, the attenuator is in 0 attenuation state, and the instrument returns to normal

4 conclusion

in practical work, "in the initial stage, there are many situations in which the test instrument does not work properly due to the over tolerance of the voltage bias at the working point, which should be analyzed in detail

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