Yep I bought two. Both, sadly, also appalling runners. Don't know exactly what the fault is - both of mine were sound chipped. The symptoms you describe are exactly what I experienced! I did get some improvement by adjusting the back 2 backs and running them slowly (less than18/28). But ultimately the motherboard failed on BOTH. My system is Peco track and a Gaugemaster controller. And if I can run Bachmann E4's and Hornby 08 shunters on my layout, although far from perfect, it can't be too bad!!!
Thankfully Hattons havent quibbled about taking them back with a cash return and I can get the removed chips re-blown.
So lets put this down to experience and get out the old Hornby/Lima class 73's - they may be poorly detailed - BUT AT LEAST THEY RUN!!