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A customer sent us a FANUC A06B-6134-H303#A all-in-one servo drive that failed to initialize after power-on. During testing, the drive displayed Alarm 20 and could not complete its self-check.
In this repair case, we will show how the fault was isolated and successfully repaired.
Watch the complete repair process in the video below to see how our technicians successfully resolved Alarm 20.
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After receiving the drive, our technicians first performed a visual inspection.
No obvious damage such as burned components, broken connectors, or damaged PCB traces was found.
The drive was then connected to our testing platform for functional testing.
After power-on:
To determine which section of the drive was responsible for the fault, we separated the side board from the main board.
The side board was powered independently.
The result was clear:
This indicated that the side board was functioning correctly.
The fault was therefore likely located on the base board.
Further diagnosis focused on the Hall current sensors mounted on the base board.
The input and output signals of both sensors were measured and compared.
Although both sensors appeared similar at first glance, one sensor showed an abnormal output.
| Sensor | Output Voltage | Input Voltage |
| Left Sensor | 2.5 V | 5V |
| Right Sensor | 2.3 V | 5V |
The output of the right Hall current sensor was approximately 0.2 V lower than the expected value.
While the difference seemed very small, it was sufficient to prevent the drive from passing its self-check and resulted in Alarm 20.
This case demonstrates that even minor deviations in sensor output can lead to significant system faults.
The defective Hall current sensor was replaced with a new component.
After replacement, the drive was powered on again.
The result:
Multiple functional tests were performed to confirm stable operation.
The repair was successfully completed.
If your FANUC servo drive displays Alarm 20 or other hardware alarms, our technicians can help diagnose and repair the unit.
We provide:
Contact us with your drive model number and alarm information, and our team will be happy to assist you.
How we process your repair requirements
Get in touch with us and provide as much detail as possible about the issue you are experiencing.
Our professional repair team will help assess the severity of the problem and the possibility of repair.
The customer sends or delivers the servo drive to our company. We register it in our system and prepare it for further inspection.
Our engineers diagnose the fault points of the servo drive and provide a detailed inspection report, including the final repair cost and estimated repair time.
We provide the repair quote to the customer and wait for their confirmation. If the customer agrees to the quote, we proceed with the repair.
Upon customer approval, we carry out the necessary repairs. After repairs are completed, we perform tests with the motor and conduct aging tests to ensure the servo drive operates reliably under various conditions. Once the testing is successful, we register the drive for delivery.
The customer completes the payment, and we deliver the repaired servo drive to the customer.
We provide attentive follow-up service to ensure customer satisfaction and address any further needs.
