Installing a DCC decoder in a Heljan Class 14 ("Teddy Bear") Diesel Loco
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Before installing chip into any loco it is advisable to check the current being drawn by the loco. You should test the current drawn when the loco is stalled to find the peak current and select a decoder that will cope with that maximum current requirement. Maximum draw with this loco on full speed on DC is 0.3 amps.
The first step in installing a decoder in this loco is to ignore the fitting instructions provided by Heljan. Their DCC installation instructions make the whole process sound very easy and it really should be - but it definitely isn't!!!
You will need two small screwdrivers, one with a flat end and one Phillips type (and possibly an electric screwdriver - more of this later!)..
First, remove the cab. It is a relatively tight fit, so pull very gently each side until it just moves a little so that you can get your finger nail under each side in turn to gradually lift it off. Beware as you do so as the horn cowlings each side of the cab will undoubtedly fall off!! Don't lose them.
Handle the model carefully as other parts are liable to fall off (such as the steps) or, even worse, get broken.
Once the cab has been removed you will need to remove the front internal panel. This sits on top of lugs each side of the main bodyshell, so the bodyshell cannot be removed with the panel in place.
Then remove the screw holding the main bodyshell in place. This became quite a challenge and couldn't be moved using a manual screwdriver, so an electric screwdriver eventually managed to release it.
Removing the bodyshell needs to be done carefully - try to lift from the central end first and ease each side away from the chassis by pulling gently so that any wires trapped between the body and chassis don't get chafed during the body removal process.
Once inside there is a mass of wires, which have been "tidied" using sticky tape. This will need to be removed.
The mass of wires needs to be gently lifted upwards to reveal the blanking plug.
It had been hoped that it would be possible to fit a plug and play decoder with no wires, such as the TCS DP2X, but there isn't enough space, in addition to which there is a screw holding the main board in place which is too close to the socket to allow such a decoder to be pushed completely into the socket.
So a wired decoder with an 8-pin plug is required and, as space for the decoder to be located under the board is severely limited, it needs to be a small decoder. First a DCC Concepts M2SAX decoder was tried, but there was unsufficient space for all of the wires and the thick end to the decoder where the JST harness fits. Eventually a DCC Concepts TS2SAX decoder was successfully installed.
However, there are a lot of wires now and these need to be tucked away carefully and secured with some tape across the top of the main board before replacing the body shell.
It is a good idea to check that everything is working correctly and program the decoder before replacing the body. Replace the body from the front end first and work towards the middle making sure there are no wires exposed or trapped.
This particular decoder is new and showed itself to have superb motor control with precise running, especially at low speeds. It's a pity the same cannot be said for the model which has a slight wobble!
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