1. A resistance ratio of the failed instance <br> <br> power load short-circuit failure diagnosis method: Fuse FANUC servo drive plate ten BESK a 15V load burn soft breakdown.
When we repaired, it was determined through preliminary inspection that the cause of the fault was a partial short circuit of the load, and the “15†ground resistance was measured with a digital meter. The normal board was 1.3KΩ and the fault board was 300Ω. Because the fuse is energized and burned, it is impossible to check the power at all, so only the resistance measurement or the component inspection can be done.
However, since the servo circuit's ten 15V power supply and its load (24 integrated components) are printed in a radial configuration, it is impossible to perform circuit cutting separation during resistance measurement, and it is impossible to directly solder because of many components. Disassemble the inspection one by one. The actual operation of the maintenance is very difficult, and even if the fault is solved, the board is often scarred. Handling this kind of failure that can not be done by circuit cutting separation or component disassembly and power failure inspection, we use the resistance comparison method to check is very convenient. During the diagnostic inspection, the circuit is not cut and the component is not soldered, but the resistance value of the relevant pin of the 1015V terminal and each integrated component is directly measured, and the corresponding value of the faulty board and the normal board are compared, and the fault can be detected. . When dealing with the above faults, considering the number of component pins, first analyze the internal circuit of the thick film block (marked in the figure) and the integrated block pin function diagram, and then select some main test points from it to do the resistance measurement. When measuring Q7, it is found that its 3 pin (+ 15V) to 14 pin (output) resistance is 150Ω (normally 6KΩ, suspected Q7 (LM339) has a problem, after replacing Q7, the servo board returns to normal, indicating Q7 pin Abnormal resistance is an internal soft breakdown, causing a short circuit in the power supply.
2. Step-by-step simulation of fast processes
Some control processes, such as the automatic lifting speed of the stepper motor, the parking brake process of the DC governor, only a fraction of a second. Looking for circuit faults in such a fast process, it is obviously impossible to use general instrumentation for fault tracking detection, so fault diagnosis is difficult. In the following, through the failure example, the 5V DC thyristor main drive has a long stop time, and introduces the special method we use a step-by-step simulation method.
After a preliminary check of the faulty board, it is judged that the cause of the fault is in the V5 main drive brake circuit. The brake control logic is complicated, involves many circuits, and the diagnosis fault is by no means an effort. Moreover, because the braking process is short and cannot be measured, we use a step-by-step simulation method for diagnostic inspection. The braking process is known from the circuit principle as follows:
(1) The bridge is inverted, releasing energy; (2) automatic bridge replacement, regenerative braking; (3) bridge replacement again, circuit recovery.
For the needs of step-by-step measurement, the speed process, speed feedback and current feedback are set as the set amount, the above process is subdivided into eight steps (listed into a table), and then the corresponding set amount is gradually changed to detect the relevant circuit signals. Check the circuit logic to find out the fault. When we do the step-by-step test to the second step (that is, the speed command changes from 1 to 0), we find that "a back shift" and "integral stop" are both high, according to the circuit logic, it should be low, according to this Check the circuit and quickly find out that there is a problem with the NAND gate Dl06 (model: FZHI01) in the A2 board. After replacement, the fault is eliminated.
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