In reply to all thanks, it is the Zen Buddha large scale decoders I am asking about, Mike's answer was the one I was looking for, I have one that blew when I switched to shunting mode, but I have a colleague who has had 2 blow after running for a period of time, I have to admit we are fitting to locos with 2 motors but the running amps of 2.4 are below the parameters set for the decoder, maybe, just maybe they should be used for single motor operation. I have emailed the company and they responded quickly to the effect that I am sending the decoder to then for inspection/repair/replace.
I have formed the opinion that Dcc conceptsuk are very good on all other scales except Large Scale, I hope they can prove me wrong.