Internal short AEC 57 switcher

If there are no pinched wires, check the E unit to make sure the drum is in place, and the unit cycles as designed. I have found that the drum wears the nubs on the side and the drum causes short circuits with the E unit fingers. 

Did you remove the motor wires?  If so reinstall correctly? G

Here is the wiring diagram for this unit. Compare your wiring to it, and check the e-unit as recommended.

Larry

rrkidder:  When you re-installed the collector assembly, you did not mention whether or not you installed the rectangular, heavy/hard cardboard insulator between the collector and the frame - did you?  Dennis M.

Dennis, yes I did.
One other thing that I forgot to mention.
I put the engine on my test bench, & wired directly from the transformer to the 'E' unit.
The short disappears, however, the 'E' unit cycles only occasionally, not all the time.

rrkidder:  one other thought: when you have the unit on your test bench, is it on a piece or two of track, or are you supporting it with the collector just hanging in air with wire jumper clips attached?   It is possible that the collector rollers are hitting the underside of the frame/chassis when it is on the track.  I would put a piece of tape on the frame above each roller to see if perhaps they are touching the frame and causing your "short"   .  Dennis M.

Dennis,
No it is not on any track, just have it sitting on the wooden bench top.
Another thing. When I apply power & the 'E' unit cycles, the engine does not move in the forward or reverse direction. The armature doesn't want to turn, but if I increase voltage I can hear it hum. I'm afraid to hold the voltage there for fear of burnout.

Take off the brushplate and pull out the brushes and springs to isolate the motor. Cycle the e-unit by hand to see that it works smoothly. Check that the fingers on the e-unit are clean, not bent out of shape or worn through, and are making contact with the drum.  Check that the drum is clean, is not worn or burned, and turns freely. Now put the car on the track and see if the e-unit cycles consistantly. If it does not, the e-unit needs service. If you still have a short , the wiring to the e-unit is probably bad, or you have a bad coil in the e-unit. If it works consistantly and no shorts, put the brushes and springs back in and try again. If the car works, you're done. If not you have a motor problem.

Larry

There is a single very small ball in the brush plate that acts as a thrust bearing for the armature in one direction.  Sometimes when the brush plate is removed the little ball can fall out.  If the ball is lost the unit will not run in one direction.  You might want to check to see that the ball is still there.  With the brush plate off the motor, I you should not beable to see thru the oil hole on top of the brush plate.  The little ball should block the hole.  

As others have posted, the problem could be in the e-unit. I had one case where one of the studs on the ends of the e-unit drum was worn away, and the drum was cocked and shorting out.

In another case, one of the tiny molded collars that are next to the studs was worn away, and the metal part of the e-unit drum was touching the metal body of the e-unit frame. On casual observation, the drum looked fine. One had to examine the e-unit closely to see that the parts were touching.

After using all of your input, the short circuit problem still exists.
However, I do have it narrowed down to the 'E' unit that is causing the short and
I will be ordering a new one on-line.
I cleaned all fingers & the drum with electronic cleaner. None of the fingers appear bent, the drum isn't cocked & is not touching any metal. I double checked the 'E' unit wiring according to the wiring diagram & it is wired correctly.
The tiny chrome ball in the brush plate head is there.
After placing the engine back on the track, I checked to see if anything other than the roller pick-ups were touching the center rail, or if the pick-up assembly was touching the center rail or the engine frame. All checked out fine there.
Therefore, I consider this thread closed and will await the arrival of the new "E' unit.
I have done this procedure many times in the past but have never run into an PW 'E' unit that gave me this type of problem.
Thanks again to everyone for their input.

When the short gets frustrating like this, I usually desolder the e-unit, then go with AC power directly to the motor with a jumper for the field winding using the wiring diagram in the PW manual.  This way I can test the motor directly.  Reverse leads to check both directions.  I have found motors that have cocked armature plates that cause binding and shorts.

You can also use 2 bulbs to replicate the motor and test the e-unit.

Let us know how it turns out.  G