At last I have received the Chinese PSU, so it is time to move.
I have checked the robot arm thoroughly. Now I can say that all is correctly mounted and complete, not so easy as it seems, hundred of little parts, and the instruction book poorly detailed on some steps.
But I can also say that it has never worked. All the effort and caution put on the assembly by the owner was not hold on the wiring phase. As a result, some of the leads are shorter than needed, directed through the wrong hole, or connected on the incorrect motor, sensor or switch.
Then, I have had a nice afternoon fixing the jungle of leads, at the end not so difficult, but I can understand the frustration of accomplishing the task without some knowledge.
Next, I have tried to feed the 4 motors with the PSU, first to one side and then to the other inverting the polarity, perfect.
One minor problem has appeared when I have feed correctly the robot arm with the PSU trough the FischerTechnick interface: one of the motor driver chips on the interface is stuck and one of the motors is always turning. This is unusual because I still have not connected the EP to the set.
I have checked the components near the motor driver chip and I have found a burned diode. I have de-soldered the component and this is a picture of the zone:
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I don't have components at my house, so more on Monday.