Weird short?

[Green_Elite_Cab]

hello!

I've been having some trouble with some Decoder installations. A friend of mine asked me to try and fix his Blue-line Pennsy M1A 4-8-2. I've found that whenever the drivers touch the rail, the locomotive either buzzes and hums, or it runs forward out of control.

I also just had the same problem with a power truck i just bought for my Arrow III EMU. the Arrow's power truck ran fine on DC just the other day, and i only installed the decoder an hour ago. However, i've still yet to find what caused this problem in the M1 (and i have been tinkering with it for weeks). Does anyone know what kind of problem this is?

It goes full speed ahead when the direction is set to forward, and it hums when in reverse, and the motor controls do not respond. The original decoder in the M1 seems to be burnt out, but after placing several other working decoders into the M1, it seems clear that there is a problem in the locomotive as well.

Any hints? whatever it is, its not in the decoder as far as i can tell.