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When fixing industrial pcb boards, the board is usually checked first for components that are obviously damaged such as blown out and smoked, and then some key components such as fuses, IPM modules, IGBT modules, rectifier bridge stacks, switching tubes, diode filter capacitors, resistors, and so on, are detected in the case of power failure. If there is no short-circuit, then power on the industrial circuit board to test the voltage of some key points, in order to find out the point of failure, troubleshooting. The following will explain in detail the basic process of industrial circuit board repair.
Step 1 Observe the faulty industrial circuit board
When you get a piece of industrial circuit board to be repaired, first of all, make a careful observation of its appearance to see whether there are damaged components.
Specific methods are as follows.
1. Observe whether the circuit board has been dropped, resulting in deformation of the board corners, or the chip on the board was dropped deformed or broken.
2. Observe whether the components on the board have been burned. For example, IPM modules, IGBT modules, switching tubes, resistors, capacitors, diodes, integrated chips, there is no bulging, cracked, burnt, blackened.
③ Observe the circuit board on the line there is no skinning, burnt broken circuit, sink copper holes there is no detachment from the pad.
④ Observe the insurance on the circuit board (including fuse and thermistor) to see if the fuse is blown. Sometimes because the fuse is too thin to see clearly, you can use an auxiliary tool multimeter to determine whether the fuse is damaged.
If the above failure, we must specifically find the cause of the failure, check the general idea is: first of all, we must carefully analyse the schematic diagram of the circuit board, and then according to the burnt components of the circuit, find its superior circuit, step by step upward derivation, and then by virtue of some of the experience accumulated in the work of analysing the most prone to problems in the place, to find out the cause of the failure.
Step 2
Detect whether there are any short-circuited components in the circuit board
For industrial circuit boards without obvious damage, to find out the cause of the failure, it is also necessary to use a multimeter to measure whether there are any short-circuited faults in the key components in the circuit before powering on the test.
The key components to be tested are shown in the figure below (listing some of the key components).
① Test the IPM module or IGBT module to see if the module is short-circuited and damaged.
2 Inspect the fuse to see if it is blown.
3 Detect whether the rectifier diode or rectifier bridge stack is short-circuited and damaged.
4 Detect whether the filter capacitor is short-circuited.
5 Detect whether the switching tube is short-circuited and damaged.
6 Detect whether the renewal diode is short-circuited and damaged.
7 detect whether the optocoupler is damaged.
8 Detect whether the resistor in the driver circuit is normal.
9 detect whether the sampling resistor in the current/voltage detection circuit is short-circuited and damaged.
Step 3 Detect critical voltage signals and waveforms in the circuit board under power-on condition
If the cause of the fault has not been found after the previous two steps, the next step is to find out the cause of the fault through online measurement. Usually in the case of determining that there is no short-circuit failure of the industrial circuit board (if you can not determine whether there is a short-circuit failure of the circuit board, you can connect a light bulb at both ends of the fuse as a buffer in the event of a short-circuit), directly supply power to the circuit board, and then detect whether the voltage at the key points is normal.
The specific detection methods are as follows.
1. Measure the power supply voltage of the IPM module/IGBT module first.
2. Measure the 15V supply voltage of the IPM module in the circuit board.
3. Then check the 15V supply voltage of the IPM module in the circuit board.
4. After checking the drive voltage, use an oscilloscope to measure whether the waveform of each drive signal is normal.
5. Measure the power supply voltage of the processor (CPU).