View Full Version : Rockwell LiquiFlo AC drive

08-07-2011, 09:38 AM
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. :confused:

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


13-07-2011, 03:32 AM
The power card on drive is unservicable, power surges etc., have corrupted everything and sundry.
Best course of action is replace total unit. Typical Allen Bradley.