Electrical Problem with Sprectrum F7 Engine

[N Scale Fan]

Greetings,
I'm having a problem with a Bachmann engine and I hope someone can give me some help. I have a New Old Stock (NOS) Bachman Spectrum N scale F7 Diesel chassis that is having an electrical problem. When I run the engine on my layout, it runs strong with no problems for several seconds. It then stalls and stops, but then starts running again. The amount of time and distance varies from one or two seconds to several seconds between stalls, and it doesn't always stall in the same locations. If I place the engine in tandem with another powered engine, it will cause both engines to stall and stop.  I have taken the chassis apart to lube it, and to check all the electrical connections and contact points. But I don't see anything that looks like a problem.  Can anyone please offer any suggestions as to what might be wrong?  Thanks...

[Mike C]

 If you put them both on the track , but do not connect them together , do they both still stall ?  If so it may be a short circuit somewhere in the F7 .  If the other loco keeps running I would look for a bad contact point again in the F7 .

[N Scale Fan]

Thanks for the response... I've had them connected and separate and the same problem occurs. Both engines will stall.... I figure it's a short somewhere in the F7 chassis.. I just can't figure out where it is. I've done a continuity check and there are no problems that I can find. I'm wondering if it's in the windings of the actual motor.   I might try replacing the motor with a spare that I have to see if the problem is internal to the motor. If its not that, I really have no idea where the problem is.

[Bloks]

If any engines stops - maybe problem is outside of this engines? Maybe power wires to tracks or power unit failed?

[brokemoto]

Do you have a amp meter?  If the amperage jumps when the locomotive stalls, either the locomotive has a short or it is causing a track short.

Failing an amp meter, what is your power source?

Some of the older B-mann SPECTRUM DC power packs had meters on them.

Many of the MRC powerpacks have a green light wired into the throttle.   Turn up the pack high enough that you can see the green light clearly.   If it blinks or dims significantly when the locomotive stalls, there is a short somewhere.

I would suspect that locomotive.  To be sure, the weight of the locomotive can cause certain track to short.   Usually, though, variations in weight on track tend to cause electrical continuity problems.  In fact, if the light does not dim or blink, you have a continuity problem, possibly in the track,

[N Scale Fan]

I've tested the engine on two separately powered (with different power supplies) sections of track on my layout, and I've also tested several of my other Bachmann F7 engines on my layout. All engines run fine except this particular one.  So, it doesn't look like it's my track circuitry.
I'm guessing it's a short internally in the motor inside the engine. The next step for me will be to replace the motor with a spare unit I have and see what happens.

[gatrhumpy]

1. Clean the track.
2. Check continuity between the track and the motor leads. Should be very low resistance. If you encounter a resistance value of 1 on either side of the track, you've found your problem. Do this on straight sections and curves.
3. Check the voltage of the track where it stalls. Check continuity between each section of rail.