Repairing PM6-600 circuits

There is a kuka krc1 robot that has "under voltage pm1" error. We can't move the robot but when we open the power socket of joint 4 we can move other joints in manual mode.

Any recommendations for repairing PM6-600 board to overcome this error? Any electronic circuit diagram and BOM part lists of PM6-600?

For more information we opened pm6-600 and checked IGBTs and their firing circuits and noticed that they are working well. We replace sockets of motor joint 4 and 5 together and the error goes to joint 5 that means the problem is not from motor side. Now we should check the PM1 board of PM6-600 that has many ICs. Is there any circuit diagram for PM1? Any recommendations for repairing this board?

Many thanks in advance for your help.

The problem finally solved. First we checked the IGBT which was working properly. And then we checked the feedback circuit and CT, which was the problem, and by repairing it, the problem was solved.