Have been working on Rockwell LiquiFlo AC drive of 643A with C- Frame. Customer called that the Breaker tripped, when reached site found One of the SCR had burst open, and two were short. All other components checked OK so just ordered the 3 SCR's and fixed on the drive. Powered the drive and it worked well for about 02 hours and tripped indicating "UbS". Checked DC bus voltage and found +ive to -ive was 76V and to midpoint was 156V. Three ceramic resistors R12, R13 and R14 are open.
And also the display on RMI went blank.

Before just replacing the resistors what other things I can check.

Thanks.