Dear Gyro_Gearloose
if the alarm is 123 drive spindle fault and energy regenerative the problem this in control tage not in source power
in the power stage do not problem
the problem this in control stage normaly in source conmuted has several small circuits that make the control in vectorial unit
i suggest check the control stage in my case there i found problem. is necesary check all elements one to one and be doing tests for detected wich elements failling.
you can feed the power unit stage whit a transformer to test this for check elements, do not for check output of the vector this can only on the machine unless you can simulate machine outside for test.
I hope this helps with your problem


regards