MTH Dash 9 PS3 shorts out

Doug,

Check your 2/3 rail wire (brown) coming through the frame from the trucks.  Also check the power wire in the same location.  And check the crimped connector on the trucks.

Dave

Thanks Dave...Guess the shell has to come off and I'm looking for a bare wire maybe? Or wire touching something it shouldn't be touching?

Yes, Sometimes the wire will rub where it passes through the frame.  Sometimes the crimped connector will cut into the next wire.  I unscrew them and grind them down.

Dave

I have a problem with my son's RailKing PS3 Dash 8 where it shorts out on most of my FastTrack O-48 turnouts. It is a very nice engine, but we can only run it on one loop because of this issue. Very frustrating.

Does it only short out on the turnouts? Can you see where it arcs or anywhere that the sideframes come into contact with the pilot or frame?

The pilot and the side frame should all be part of chassis ground when in 3R operation.  Is the switch in the correct position?

If this is new I would have it serviced under warranty.  Otherwise you are looking at removing shell, detaching motor from truck to get a good look at the wires Dave mentioned.

Then tracing through engine to switches, etc....   G

The switch is in the correct position, it does run. Just in the curves it was touching and I could see the arc. I have no problem removing the shell, had to do it a few times with my Dash 8's for another matter.

I figured the sideframe and chassis are ground, that's what led me to believe that something, somewhere else is touching something it shouldn't. Like a bare hot wire when it goes into the curve. Not to mention the additional arch when coupling to another kadee coupler...it arc'd well enough to burn out the knuckle spring on the 805 coupler on the car. 

 If your are using the KDs with the metal box and metal coupler, sure, power will flow right thru.

 Dave's suggestion is a good one. I've found a few engines with wiring problems. I'm surprised that it just doesn't shut down rather than throwing sparks? I wouldn't run it until it's fixed.

Just my opinion, but the above statement might definitely be your clue to what may be "powering the frame". If you think about it, the metal Kadee touching a metal Kadee on a freight car that MUST have a metal frame & metal trucks, is shorting directly to the outside/common rails. 

I agree with the suggested investigation paths, provided above.

Yeah Joe and hot Water, the transition car I was using had a metal frame, metal Kadee with a metal draft gear box. So the coupler was in contact with both outside rails. I switched to a different car with a plastic frame and eliminated that problem. When the Dash 9 side frame came into contact with its own pilot and arc'd, it would kick the breaker on the 180 watt brick. It left burn marks on the side frame and the pilot as well. There was not even a car coupled to it at that time, just a light engine move. 

Still have to take off the shell of the Dash 9 to figure out exactly why the frame has become "hot". It's gotta be a wire.

I have read where some people use the plastic draft gear box on engines to avoid having this issue. I completely understand the concept for 2 rail equipment..that one is kinda obvious, but with 3 rail you shouldn't "have to" use the plastic box.

 I had one engine that acted up on left turns only. It was missing a plastic insulator deep inside the truck where the power pickup is. A piece of shrink melt slid down over the metal piece worked to insulate this.

 All the others were wires that were shorting from either rubbing, crimped, or not assembled correctly at the connection to the truck.

Well whatever the problem is, it's isolated to the front pilot. I was checking around with the volt meter, and the rear pilot and coupler are fine (no voltage flowing through). If I put a probe on the outside rail (common) and touch the other probe to the front coupler or pilot, I get a full track voltage reading.

I'm thinking it might be the wires going to the ditch lights, as those wires are run right through the front pilot. If the whole frame was "hot", I would have voltage on the rear coupler and pilot as well.....right?

I believe you are on the right path to discovering the root cause.

 Well, if I'm thinking right, that should be easy. Push the direction button and the ditch lights go out. See if you have current still.

Well so much for that.... front pilot and coupler have voltage at all times, whether or not the engine is forward or reverse, ditch lights on or off!

**** I hate taking these things apart!

For PS-2/3 engines the accessories such as lights, couplers, and smoke have a High positive volatge available all the time via the purple wire (PS-2).  The other lead is return to PCB Ground via a FET.  So even if ditch lights are turned off, the PV is there via the purple wire.

Look for nicks in the wire.

But frankly, if the PV wire was shorted to chassis ground you would know it and see it as an overload on the AC side.  G

Well I will check that out, because it sounds like that's exactly what it is. Although the voltage is there at all times, if the engine moves just right, it does pop the breaker on the 180 watt brick.

Yeap, that's what I get for thinking! Forgot how they work.

Well I got the shell off, and removed the pilot (fixed pilot). There is a red & black wire going to each ditch light. Not sure which one carries the positive voltage at all times, but directly under the pilot, the black wire has a bare spot in the insulation and some of the strands of wire are smashed against the pilot. I assume this is what is causing the front coupler and pilot to carry voltage through it. You can tell the wires got hot because the insulation, especially on that black wire looks like it was trying to melt. 

I'm not sure if I can get some shrink tube around the wire because space is already so limited in there. I already removed the cab figures as I will most likely run this as a middle unit in a 3 or 4 unit consist anyway. I may just pull the wire plugs out where they connect to the connector in the shell.  

Thanks GGG and Joe...got it fixed. Apparently that black wire was sending juice right into the pilot. I used some AC glue to create some insulation and also AC'd the wires down to the shell under the pilot so they can't touch again. No more voltage in the coupler or the pilot, and the ditch lights do work if I want to use them.... although there's no crew in there now to run it as a leader