I have a 627 from the 50's - which has been sitting on my (no deceased) father's workbench apart for 10+ years. He took it apart to fix it and never got back to it.
So I picked it up, and I remember what the problem was. The motor will not turn - it only hums and vibrates regardless of polarity. I am jumping the motor direct to the transformer to both brushes - so I have taken the "E" unit out of the equasion. Motor turns freely by hand. The brushes look OK - I swapped them left to right just to see if there would be any difference, I cleaned and polished up the top of the armature with no change. Aren't these motors pretty simple? What am I missing - anyone have any ideas?
Do not connect the brushes directly to the transformer. The motor will not work and you risk burning out the armature windings. Connect the brushes in series with the field winding. One end of the field winding is probably connected to the motor frame. Connect the other end to one of the brushes. Then connect your transformer between the frame and the other brush. Then the motor should run. To run it in the other direction, swap the connections to the two brushes. (This is what the e-unit does when it is in the circuit.)
Bob Nelson
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