Here is the trailing unit opened up.  No burned parts or loose wires.  The Aluminum bracket that supports the board and doubles as a heat sink was loose.  The screws that attached it to the frame were not tightened and it wobbled, but the board was not contacting any metal parts.

Running the unit without the shell, I found that the flywheels spin slowly in opposite directions, so I put the units back up on the rollers.  Here I found that the trailing unit actually moves, but at about half the speed of the lead unit.  The trailing unit does not start moving until 14 smph in forward and 10 smph in reverse.  The motors spin freely by hand, they don't seem to bind.  I pulled the motors and the worms are well greased and the grease is soft.  So at this point I'm planning run them for an hour to see if they can be broken in.

Bob

Turn motors by hand to ensure they are not binding.  You can watch motors with shells off to see if one or both motors not spinning.  Slave needs the motor signal from the lead to work.  Could be open wire in lead A or Trail unit, or bad board.  Board can be tested.  G

Now I looked closer at the lead unit. It had a lot of truck noise, so I opened it and found a loose battery flopping around.  I pulled the motors.  The grease was fine. After reassembly, the noise was gone.  All 4 motors spin and none felt like they are binding when turned by hand.  It is running smoother now, though there is still a speed difference between the units. Also Traction tires are ok.

I'm going to break them in and see if that corrects the speed difference.

Bob

George -

Does the slave board get ground from the bracket/heat sink?  If so, that might have been the problem when I initially tested it on rollers and got no motion from the trailing unit.  The mounting screws were started, but never tightened.

Bob

If your not going to pull especially long or heavy trains with this double unit, I'de just pull the motors of the B unit.

Why not?

Bob , on the center pickup rollers I usually clean up the outside of them really well.          I then have the engine on its side and apply contact cleaner to the inside of the pickup roller and work it back and forth to see if I  get a lot of gunk coming out between the roller and the roller pin.

I will then put my rubber  wheel on the Dremel , apply contact cleaner ( or your choice of cleaner ) and run the roller with the rubber wheel . Once I am satisfied that there is not a lot of black residue coming out I then use a small amout of light oil on the roller pin.

On some of  my PREOWNED ps2 / 3volt engines I find getting these pickup rollers in good shape has made a big difference in performance.

.....just my two cents.

I have had issues with "wheel dragging" on trailing power units with a slave board and found cleaning the brush blades and commutators in the can motors to be helpful. Try using electronic contact cleaner and target the red spray tube at the brushes.

A tiny paint swab dipped in naphtha will also work, just be careful you don't bend a brush.

@RRDOC posted:

George -

Does the slave board get ground from the bracket/heat sink?  If so, that might have been the problem when I initially tested it on rollers and got no motion from the trailing unit.  The mounting screws were started, but never tightened.

Bob

No, it only gets power, ground, and signal via the wired connectors.

Resolved!

I took Scott's suggestion and sprayed the brushes in the trailing unit.  It did improve in that they started moving earlier.  I still had chattering of the lead unit from dragging the slave unit.  No problem running in reverse.  

At this point I decided to break them in, first running them backwards, and then forward.  After an hour of running, the chattering improved.  I was only occurring between 5 and 15 smph.  

I wanted to do more break-in of the slave unit only so I pulled off the shell again, put it up on rollers and powered the motors directly with the 5v DC output of an ATX power supply.  After another hour or so, I put the units back on the track and most of the chattering has resolved.  

So, bottom line when you have chattering of a truck from dragging the trailing unit, here are some things to try:

1. Lube the axles
2. Remove the shells and check wiring
3. Rotate flywheels by hand to check for binding
4. Pull motors and check for grease
5. Spray brushes with electrical contact cleaner
6. Break in the unit (run backwards at first, or run the trailing unit motors directly with DC)

Bob