I' have a Williams NYC shark nose thta I'm tryi9ng to repair for a friened. I need to hear from someone who understands its electrical system. I know nothing about post-mechanical reverse units.
The basic problem is that the unit shorts when power is applied to the reverser, but not when I apply power directly to the motors. I've taken motors and reverser off the frame so they are electricall y isolated from the trucks and frames, ruing out problems there.
The can motors are mysterious, having only tow connections apparently just to the brushes. I don't see a field winding, just tow circular pieces of metal. In a DC motor they would be permanent magnets, but these don't seem to be as they won't attract a paper clip. So how is the field generated.
I'm amazed by the reverser board. How can you need 13 resistors, five capacitors, four heat sink transistors, two small transistors and two 14 pin chips to do what used to be dowm with a very simple electro-mechanical device ?
Here are the tests I ran. A and B refer to pairs of brushes on a single connection to the reverser. Ground refers to the outside of both cans.
1. Power to brush pair A and ground, with both brush pairs connected to the reverser board - both motors run.
2. Power to brush pair B and ground, with both brush pairs connected to the reverser board - motors are dead.
3. Power to both brush pairs disconencted from reverser - Armatures rotate only enough for brushes and field to be aligned and then remain stationary.
4. Power to reverser connection to frame and pickups - short circuit.
Does this suggest to anyone what is wrong ? Do I need a new reverser ? One obvious option is to connect the motors as in test 1 and fun forward only.
I would much appreciate any insight into how this system works electrically and what might be causing the short.
Malcolm Laughlin
