HAAS HFD4 Vector Drive Repair

 

I was requested to visit one of my customer's premises to troubleshoot HAAS mini mill machine. HMI was displaying error alarm 119,177 and machine could not be started. when vector driver was replaced with new one, problem solved. therefore vector drive may have some error and brought it to my workshop.

First of all, all parts of the drive were cleaned.

             

 

the problem was clear. machine sends overvoltage alarm when supply voltage is within safe limits. unit gives the error when on stable DC bus of 312V.

therefore we can directly point to the voltage detect section of the motherboard.

According to the circuit diagram, the opto-isolated op amp circled in yellow(A) is the main part that responsible for voltage measurement.
HCPL-7800A has two supply voltage inputs. both supplies are looks ok and stable 5V detected. op-amp has differential output directly connected to LF411 op-amp(B). output of LF411 measured 4.2V, seems has the fault. because it must be lower the shown value.

Without experimenting much with the circuit, i replaced the HCPL-7800A to check whether it was the actual fault.

After replacing the 7800A, the output of LF411 became 2.8V and looks normal.

I handed over the drive to customer to install into the machine and see the actual result. Ploblem solved.