I have found an error in the HP41 repair book - in the part referring to the card reader repair.
It is about the order or the cables leading to the electric motor. The black cable is the one furthest from the calculator; the red one is the closed to the calculator. The book said the opposite (or could be understood as the oppositce - it is strange to me since I knew the right order!
Here is a picture illustrating what I say: it is the two cables on the left. The upper part is towards the calculator.