The first step was the preliminary static test to check for any obvious shorts or opens in the converter and inverter side of the motor drive unit. The defective component, a shorted SCR on L1 input in reference to the DC bus line, was identified and replaced. We also recommended that the other two SCRs be replaced as a precautionary measure. The failed SCR had caused electrical and heat stress to the remaining SCRs, and replacement would avoid another failure and additional downtime.
Once all three SCRs were replaced, the drive was operated under load at nominal amperage to fully test the drive unit and confirm that the repair was successful. We also advised the customer to continue using the recommended fuses for their system. Replacing the fuses with a higher amp fuse cause concern as they act as the weak link in the circuit, and a higher current can cause catastrophic damage to the system.