Philbyw

I have a problem with a GM dcc26 opti decoder that I have recently purchased, it is only being used for the speed control and no lights etc. on my loco, My DCC system is Digitrax. When I have fitted the decoder it will only move in a stuttery manner stopping and starting in a random fashion. I have cleaned the track and the loco all to no avail. I have even swopped it over to a loco that runs fine but has the same issue show up when fitted with the GM decoder stopping and starting randomly as though it is running on a dirty track. If I use another make decoder in said loco's such as Bachmann or Digitrax there is no problem. I have tried changing C.V.'s etc or re-setting the decoder but nothing seems to cure it. I have read somewhere that there may well be a problem with these later made GM decoders earlier models were ok apparently, Help please it is driving me round the bend!