The powerhouse works the same as a more simple two pole shoe design except it has three poles on one side and three poles on the other, ie north and south sides. This gives it a wider variation in the field flux that act on the armature. Since the field is controlled by it's own brush then pushing the flux distortion closer to the power output brush will increase the amount of current it will pick up off the armature. This link illustrates how all 3-brush units are configured in basic function. The only difference is that the field doesn't control the cut out on the model A designs. It comes from the armature output.
http://www.vias.org/kimberlyee/ee_31_02.html
If there is magnetism in the pole shoes with proper polarity and all the elements of the circuit are sound and functional then it will generate current. Voltage is held to the battery voltage by the way it is designed.
If any connection is weak, shorted to ground, open circuit, or the polarity of the fields is incorrect then it won't generate a proper voltage or current.
Were the field coils replaced or worked on for repairs?