Athearn Locos

The problem could be with your Athearn locos.  Athearn frames conduct electrical pick up.  When running on my old DC layout I noticed a lot of electrical sparking between the metal KD couplers between two Athearn units.  There was one spot on the layout where a consist of Athearn SD40-2 would always stall.  When runing in an Athearn-Athearn consist some times the rear unit would push faster, causing the couplers to droup just enough for the metal pins on the KDs to make contact with the rail, causing a short.  It would not do this when I had an Athearn-PK2 consist.  I found this out by running the layout in the dark, and the sparking was quite evident.

I like the Athearn units as I need to build a large fleet of SD40-2s.  As I am converting the units to DCC, I am replacing the Athearn metal coupler mounts with plastic KD coupler boxes.  The new Athearn Genisis units have plastic boxes already.

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A section with turnouts, cross-over, X-crossing ?  Curved, strait ? 

Something  is surely shorting ou; truck contact with  frame,  Kadee coupler pin contacting  rail. Double head could be as Jim says.  In a  single engine setup,  must be shorting to something   Single engine should not cause a current in rush issue on a PM42.  You do not state if the engines are sound equiped or not.   If you physicaly invert the engine, does it make a difference.  

Marc Fournier, Quebec

Have you checked the wheel

Have you checked the wheel sets to make sure one wheel isn't out of sorts like To WIDE or To NARROW and when you go through the frog the wheels are not touching to many rails at the same time?

Dan

To summarize what to check for:

1. Check wheel gauge

2. Check for possibility of trucks shorting against the frame in either direction.

3. Insulate your couplers with plastic draft gear boxes.  Don't use Athearn sheet metal coupler clips on locomotives.

4. Make sure the corners of the frames don't touch on any curves.  This could happen if radius is too tight.  If you    have a tight radius that cannot be avoided, you can either restrict that section to 4 axle power that will work better or make sure your Sd 40-2s are always run "elephant" style.  Note, the locomotive may work and tolorate a tight radius, but if the overhang causes the frames to touch at the corners, the radius is too tight for reliable operation.

5. Check clearances on all live frogs, guard rails, etc on switches to make sure that they are not too tight.  It might be that the Athearn wheels are slightly thicker than other brands, and more critical if the clearances in switch parts are tight.

6.  Make sure cast metal details on the pilots like snow plows are not making electrical contact with the frame, and are high enough that there is no place where a "vertical curve" could cause the plow to short across the rails.

Thanks for the advice

Jim, Marc, Dan & Russ thanks for the comments.  I will work through them in order to sort my problem which is occurring anywhere in the three electrical blocks connected to the one power section.  It even happens on straight track on a level surface.  I had a few minutes yesterday and ran them in the dark but could not see any arcing.

I will persevere with finding a solution based on the advice given by you guys.

Thanks again, Jim

I have this problem too

Hi Jim.

I have this problem too.  No offence to these other guys and their suggestions, but they are not comprehending the problem.  I have an all Digitrax system that includes 3 pm42's.  If your problem is the same as my problem, the locos will start, but once the throttle increases, or they encounter a load, the pm42 starts detecting shorts and restarting in a continuous cycle.  On my layout this would only happen with three or more locos in a consist, and it seemed to not matter the make of loco or decoder.

I too would like to get to the bottom of why this is, but haven't taken the time yet.  I will say that I "fixed" it for now by turning up the amp limit of the pm42's to 6 amps in the opswitch settings of the pm42.  No problems anymore with the consists.  The Digitrax literature says that the factory setting should be adequate for all but the most extreme layouts and consists.  I say BS to that!  If you get a good answer please post it here.

Since we're talking about Athearn SD's

Since we're talking about Athearn SD's here, I thought I would pass on one "tweak" I make to help these locos track better. If you don't do this, the trucks tend to climb the rails and then the loco runs with the truck derailed and slightly canted at an angle down the track - which also can cause shorts.

I take the middle wheelset out of each truck and use a motor tool to grind about 1/32" off each end of the axle. That part of the wheelset axle is tapered - I essentially grind away most of the tapered ends.

When I re-intstall the center wheelset, it now has a lot more side-to-side play, which helps the 6-wheel truck track much better on tight model curves.

I do this to all my Athearn SDs and they track much better with this slight modification.

PM42's replaced!

I replaced all three PM42's with PSX's and everything works correctly now.

Thanks for all the advice received.