As proof that I don't learn from my mistakes - I am an absolute sucker for new models. The rational part of my brain tells me it will mean frustration and expense but that never seems to get control when something nice appears on the website of my favourite Internet retailer.

The latest example of this is the lovely looking Heljan railbus in dark green with speed whiskers. Ordered it on a whim earlier this week and as soon as it arrived I attempted to convert it to DCC.

It is nicely packed in the standard Heljan box, it is also a wonderfully heavy model - there is a real heft to it.

To fit the DCC decoder, the first job is to prise off the two airhorns - to reveal two fixing screws - it is quite hard to do this without damage - I found a scriber was the best tool.

The hardest job then is to remove the top half of the body - note the instructions in the box do not mention that you MUST carefully remove one end of the two metal hand rails or when you split the body they will fly across the room.

You have to prise the bottom of the doors away from their seating and slightly outwards to allow the top to come off - this is really hard to do without damaging the bottom of the door (which you can see from the phot I did despite using the recommended tool of a scalpel).

Then undo the little plastic keeper plate that runs the length of the body by undoing two crossheads that hold it down.

Now you can gently lift up the centre circuit board which holds the DCC decoder and remove the dummy board. BE VERY careful - the wiring to this board is incredibly delicate and if you pull one off the metal roof that many disappear into it is impossible to repair them (I speak from experience).

Now you can fit a decoder - here is a TCS621 which seems to work ok. Note that (at least in theis case) the decoder needed to be inverted compared to the dummy board.

Here is my disaster a broken red wire that I was unable to repair - argh!!! return to sender!