Test run failure of the CHRH-415AEE Rihong VSD

Repairing the Shanghai Rihong CHRH-415AEE 1.5kW machine, the user reported unstable output and motor jumping. The output module and output module are both normal. After cutting off the power supply to the inverter module, in order to check the quality of the inverter pulse conveying circuit (including the driving circuit), they were installed as a complete machine on the maintenance bench (without the machine cover installed) and powered on for inspection. The operation panel displays normally, but when starting the operation, it jumps E OH means overheating. The thermal signal output terminals of the short-circuit modules T1 and T2 are invalid. Disconnect the thermal signal terminal and connect the original wiring terminal to the potentiometer for voltage regulation. The test is also ineffective. Check the internal circuit diagram of the module. The terminal is only equipped with a thermistor (10k at zero degrees Celsius), which is connected to an external+5V resistor to divide the voltage and directly send the signal to the CPU. According to room temperature, this partial pressure point should be below 2.5V. The measured voltage is 2.3V, and the built-in thermal element and circuit should be normal.

Later, it was discovered by chance that a small square shielding iron sheet was wrapped around the back of the operation panel. When pressing the operation panel, one corner of this iron sheet touched the 41 pin of the CPU, which happened to be the input pin for the overheat signal. Therefore, pressing the button on the operation panel inputs a module overheating signal (disturbance generated) to the CPU, which is truly a coincidence.
A piece of cardboard is placed between the operation panel and the motherboard circuit, so that when operating the panel, it no longer jumps OH fault code. The fault was quickly identified as a faulty driver circuit, and the machine was repaired by replacing it with a driver IC.