ATV66 internal fault causes.
The +15vdc and - 15vdc power supplies are below +/- 11.5vdc
Before making any voltage checks make sure you have removed mains voltage from L1 L2 and L3 and install single phase voltage (mains power) into CL1 CL2 minus any jumpers.
Check the +/- 15vdc supplies on J9 connector pins 3, 4 and 5
Pin 4 is 0v
Pin 3 is -15vdc
Pin 4 is +15vdc
if any of these voltages are below +/- 11.5vdc you will get the internal fault code.
Possible problems: can be
LEM's or CT's might be shorting out power supplies
Shorted gate driver boards
Shorted or inoperative power board