When installing a Digitrax decoder (in this case a DN125) the instructions say to remove the filter capacitor where installed.

I have a Bachmann N Scale N&W J Class 611 with the PCB in the tender, which ran fine in DC analog mode on my Digitrax DCC system. I installed the Digitrax decoder onto the PCB and desoldered two capacitors C1 and C2. The decoder programmed okay, but the engine will not run. I assume that one of the capacitors has to remain, but I don't know which one.

Has anyone successfully installed a wired decoder to the J Class 611 tender? Which capacitor should be removed, if any?