Issue with Quantum Revolution-U decoder


I have the above decoder (product code 4050-718) installed in a Proto 2000 2-8-8--2 Mallet.

The unit used to work well on both DC and DCC. The loco has been in storage for 4 years whilst we moved house and a new layout built. The layout is not yet set up for DCC and I have tried to use the loco on DC but the only action from the decoder is for the sounds to start up and lights to glow (dimly). I have confirmed that the plug between the loco and tender is securely installed but with no change in the decoders response. the wheels and track are clean and other sound equiupeed locos I have work well on the layout in DC mode.
On other forums they talk about a factory reset with a magnet and I have passed a magnet over the loco and tender but one again with no change in the decoder

Does anyone have a suggestion?

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