Decoder install on 4-8-4

[Kelly]

I have an Bachmann 4-8-4 and I will be using the MRC 1823 Decoder and the MRC Blackbox to control it, on a DC layout. The motor is already isolated from the frame. There are three capacitors ( red arrows ) on the motor and two resistors. My question is, do I need to remove the capacitors?
  Thank you for your assistance.

[Eryalen]

I have the same locomotive and did the conversion using a Digitrax DH123. I took out the cap's but left the resistors (0.47 ohm, I think). It worked fine without the cap's on DC even before I installed the decoder. If your decoder power to motor is supersonic the cap's would appear as a short. RF suppression is most likely built into the decoder .

[Yampa Bob]

I can only confirm that genuine Bachmann decoders are designed to be compatible with the noise suppression components on their circuit boards.

I cannot confirm or deny that other brands of decoders are compatible with these components. or that other brands have built in RFI or EMI suppression.  Fact is, I don't think other manufacturers, whether locomotives or decoders, are overly concerned about noise suppression, especially in the U.S.

However due to increasing population density, we may see stricter regulations similar to those in European countries.  All it takes is for a few people to complain about specks on their TV, (probably caused by some other household appliance) and the ball starts rolling.  Moral of story: If you live in an apartment served by common electrical transformers, don't let the neighbors know you have trains. 

[Jim Banner]

Kelly, definitely remove the capacitors.  Even if your decoder is not ultrasonic, they are not needed.  Leave the "resistors" in place.  Or if you need the space, replace them with wires.

It is more common to see choke coils in series with a motor than resistors, and there are some chokes that look just like resistors, epoxy dip and all.  But chokes often (though not always) have a green body and the colour stripes often don't make sense for resistors.  But no matter, if they are chokes rather than resistors, leave them in anyway.