I can only find a list of conformance warrants, not compliance warrants. https://www.nmra.org/nmra-conformance-warrants
Confusingly, it says ......... to ensure that these products are in full compliance to NMRA requirements.
Not sure but having both is quite common. Bachmann have both on most of their locos, using up to 3 capacitors on the motor and a choke in series with each motor feed wire. I suppose they use whatever they need to use so that they pass the RF emissions requirements.
A choke (modern name is an inductor) is almost the exact opposite of a capacitor in electrical terms.
A capacitor blocks the flow of direct current but will allow alternating current to flow.
A choke (inductor) allows a steady direct current to flow but blocks alternating current.
Ordinary card may not be the best thing to test spray onto. Plasticard would be better as it is not absorbent like cardboard and is a similar surface to what you will be spraying.
You probably just need to adjust a CV or 2. I think it's something like setting CV 150 to 0. You will need to check the instruction to be certain ( or wait for someone else to confirm CV )
Is the op absolutely certain that it an R8249 decoder and not the earlier R8215 decoder which didn't support long addresses? The two decoders look identical apart from (possibly) different colour paint blobs on the main chip.
That's the same as the one provided in my (Brand new) Powercab kit a few years ago. It is the upgraded power supply. I believe the earlier version was only 12v and there were many complaints about slow running locos.
The ground in scrap yards i visited in the early 70s and 80s were all black with a hint of blue from all the oil and grease. Modern scrap yards have hd to change their processes to avoid creating pollution.
It could be a faulty lead from the Powercab to the connection panel or the "prongs" inside the connection socket. All power to and from the handset goes via the handset cable and socket on a basic Powercab installation.
You may be experiencing the problem of common cathode Led wiring on the non sound fitted model and common anode Led wiring on the sound fitted model, or vice versa