This is as easy as it gets - Heljan have made their Class 47 DCC-Ready which means you can just plug a decoder straight in. No soldering is needed, in fact no tools at all, although a few scraps of cardboard might help you seperate the body from the chassis. There isn't even a need for these instructions, they're just here to show those thinking about taking the plunge how easy it can be.
Decoders are an area where tastes will vary, but the Lenz LE1024E suggested here is an excellent performer and extremely well matched to this loco - it's the best place to start if you haven't already developed your own opinions. I've converted 24 Heljan Class 47s so far using this chip (or the electrically identical LE1025E) and can confidently recommend them.
Photo 1
All you need. The loco, a decoder with a standard NMRA plug and the double-sided sticky pad supplied with it. The decoder used in the photos is an old Lenz LE104XF (all I had available at the time) but I would strongly recommend the Lenz LE1024E as a good match for this loco. If your model is brand new then it might be a good idea to test-run it before proceeding in order to check everything is OK.
Photo 2
To be honest the most difficult part of some conversions is persuading the body to part company with the chassis. The Heljan 47 is by no means the worst offender in this department but some examples can be a little tricky depending on the amount of flash on the chassis components. The body is attached to the chassis by four tabs (circled in red in the photo) moulded on the inside of the body itself.
Photo 3
If you slide your fingernail between the body and the chassis to disengage the tabs then in theory you should be able to pull the two apart. Unfortunately there are 4 tabs and you've only got 2 hands, so you might find it useful to slide a little piece of cardboard into the gap every time you release a tab to stop it popping back in place as soon as you move onto the next one. Once this is done you will be able to pull the body off, although it'll probably be a little reluctant to move. Gentle wiggling is the order of the day!
Photo 4
Once the body has been removed you should have unrestricted access to the circuit board where you will plug the DCC decoder. For later reference the front of the loco (or number 1 end as it's known) is the end with the DCC socket in the photo and the equivalent end of the body is that with the two circular grilles in the roof. After the conversion your loco should move in this direction when you tell it to go forwards.
Photo 5
A close up of the circuit board shows the lime green coloured dummy plug fitted to the DCC socket. Just pull it out and you will see...
Photo 6
...the actual socket (the black thing with 8 silver holes in the centre of the photo) where the DCC decoder will plug. Keep the dummy plug somewhere safe just in case you ever want to convert the loco back to conventional control. Although I forgot to do it for the photographs, the capacitor (yellow boxy thing labelled 1NJ400) should be removed at this stage using a pair of pliers.
Photo 7
Whilst the performance of the Heljan Class 47 is normally exemplary, the odd one or two can behave in a peculiar fashion as a result of the pins & solder on the underside of the circuit board shorting out against the metal chassis. As a precautionary measure, while you've got the body off the loco, lift up the circuit board and slap a piece of insulating tape over the offending areas - better safe than sorry. The black tape in the inset photograph is my 'fix' and the smaller piece of yellow tape is original Heljan.
Photo 8
The moment you've been waiting for - simply plug the decoder into the socket. It's as easy as that. Pin 1 (with the orange wire) should go towards the top right in this photograph, but if you get it wrong the loco will merely run backwards and the lights won't work - you won't blow anything up!
Photo 9
Finally, stick the decoder down using the supplied double-sided sticky pad. Make sure none of the metal components can short out against anything in the loco and that the wires don't foul anything. In the case of the Class 47 this is pretty straightforward as there is plenty of room to manouvre.
Before putting the body back on the chassis it's as well to check that everything is working. The safest way to do this is to put the loco on the programming track and try and read information from the decoder - the instructions for your particular DCC system will tell you how to do this. If all is well (and I've never yet had a problem) then pop the body back on and make sure it clips fully into place. Be very, very careful not to damage the delicate lamp-irons that protrude from the top of the buffer beam.
From a performance point of view, the Heljan Class 47 has established itself as my favourite piece of mainline motive power. Running is superb at all speeds, especially with the decoder used above, but there are a few things worth bearing in mind if you want to continue to get the best from it, whether running on DC or DCC:
Firstly, make sure you guard against possible short circuits as in Photo 7 above.
Secondly, make sure all of the electrical pick-ups actually touch the wheels, bending them slightly with a pair of pliers if there's a problem. Regrettably this is an area in which most manufacturers' quality control seems to be lacking, and Heljan are no exception.
Thirdly, keep the wheels clean. If performance deteriorates or becomes erratic with Heljan 47s it's almost always because of dirty wheels - a few minutes work will restore everything to normal.
Finally, these locomotives do seem to draw significantly more current than most of their competitors. This isn't anything to worry about (I've tested the stall current of every single one of mine so far and they're all within the limits of my preferred decoders) but it's something to bear in mind. If you find your loco mysteriously blows decoders on DCC, or trips the overload cut-out on DC, then it could be that you have a rogue sample with an above average current draw. I would stress that this is an unlikely occurrence, but I have heard of examples - if it happens to you then return the locomotive for replacement.