Troubleshooting and Repairing the Shanghai Rihong CHRH-415AEE 1.5kW Variable Speed Drive (VSD)

Repairing electronic equipment, especially complex devices like variable speed drives (VSDs), often requires a meticulous approach to diagnosing and solving issues. A recent repair case involving the Shanghai Rihong CHRH-415AEE 1.5kW VSD highlights the importance of thorough inspection and the unexpected twists that can arise during the troubleshooting process.

The user of the CHRH-415AEE VSD reported experiencing unstable output and motor jumping, indicating a potential issue within the drive’s operation. Initially, the output module and other critical components were examined and found to be functioning normally. This preliminary check ruled out any straightforward hardware failures, prompting a deeper investigation.

To delve into the problem, the inverter module was disconnected from its power supply. This step was crucial to isolate and assess the quality of the inverter pulse conveying circuit, including the driving circuit. The VSD was then reassembled as a complete unit on the maintenance bench, without the machine cover, and powered on for inspection.

Upon powering up, the operation panel displayed normal readings, suggesting that the basic functionality of the control interface was intact. However, when attempting to start the operation, an “E OH” error code appeared, indicating an overheating issue. This was puzzling, as there were no apparent signs of overheating, and the thermal signal output terminals of the short-circuit modules T1 and T2 were not active.

To further investigate, the thermal signal terminal was disconnected, and the original wiring terminal was connected to a potentiometer for voltage regulation. This test, however, yielded no significant changes, and the overheating error persisted. At this point, it was necessary to consult the internal circuit diagram of the module to understand the signal flow and identify any potential anomalies.

The circuit diagram revealed that the terminal in question was equipped with a thermistor (rated at 10k ohms at zero degrees Celsius). This thermistor was connected to an external +5V resistor to divide the voltage, which was then directly sent to the CPU. Based on room temperature, the expected voltage at this point should have been below 2.5V. Measurements confirmed that the voltage was indeed 2.3V, indicating that the built-in thermal element and circuit were functioning correctly.

Despite these findings, the overheating error continued to plague the VSD. It was at this juncture that a fortuitous discovery was made. During the inspection, it was noticed that a small square shielding iron sheet had been wrapped around the back of the operation panel. When the operation panel was pressed, one corner of this iron sheet made contact with the 41st pin of the CPU. This particular pin happened to be the input pin for the overheat signal.

The contact between the iron sheet and the CPU pin was creating a false overheating signal, essentially tricking the CPU into thinking that the module was overheating. This was a highly unusual and coincidental issue, but it explained the persistent “E OH” error code. To resolve this problem, a piece of cardboard was placed between the operation panel and the motherboard circuit. This simple yet effective solution prevented the iron sheet from making contact with the CPU pin, eliminating the false overheating signal.

With the root cause identified, the focus shifted to repairing the faulty driver circuit. It was determined that the driver IC (integrated circuit) was likely responsible for the issue. The driver IC was replaced with a new one, and the VSD was reassembled and tested. After the repair, the VSD performed flawlessly, with no more overheating errors or unstable output issues.

This case underscores the importance of meticulous inspection and the willingness to explore unconventional possibilities when troubleshooting electronic equipment. The repair process not only required technical knowledge but also a dose of creativity and persistence to solve the puzzling issue. In the end, the successful repair of the Shanghai Rihong CHRH-415AEE 1.5kW VSD was a testament to the power of thorough diagnostics and innovative problem-solving.