I've got a Mantua 0-6-0T DCC equipped, which has stopped working. On the program track it reads all of its CVs with no problem, it also runs OK on a DC track (runs forward & reverse with headlamp). However it does not respond to any commands on the DCC track, won't even turn on the head light. I've reset it to the factory defaults, but get the same results. Any thoughts as to what may be wrong and how to fix it?