Installing a DCC decoder in a Heljan Class 28 Loco

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Class 28

Before installing a decoder 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.

With a plug and play decoder installation into this loco should be one of the most straightforward decoder installations. It was decided to use a TCS DP2X-UK decoder for this installation.


Class 28 body removal

The most difficult part of the installation is removing the body. It is a VERY tight fit. There are lugs each side securing the body to the chassis. Usually it is possible to use finger nails to lever Heljan bodies away from their chassis, but in this case it was necessary to use pieces of very strong thin card and/or plastic to keep the body away from the chassis whilst attempting removal. Once the body has been moved a little each side it is possible to gently move it by rocking it from side to side, at the same time pulling the body upwards.

It was noted during the body removal that a number of parts on the loco are susceptible to falling off and/or being broken, such as the delicate pipework underneath the chassis and fitments on the bogie assemblies. One positive move on this model is the way the battery box is screwed to the chassis, so it doesn't come away in your hands as is often the case with Heljan models!! This is also very important as the battery box is one of the few solid parts of the loco you can use to grip whilst trying to remove the body.

Class 28 DCC socket location

Once the body has been removed it is obvious where the 8-pin plug on the decoder will go. Gently remove the 8-pin blanking plate from the circuit board by levering out a little from each end of the plate.

Class 58 with TCS DP2X-UK decoder fitted

Decoder overlapping resistors

Fitting the decoder plug is straightforward. However, pin 1 is not marked as such, either on the decoder or on the circuit board of the loco but the board does have the letters NMRA right next to the pin 1 socket.

If the decoder is installed the wrong way round it is not a disaster as the plug can just be removed and installed the other way round. If it has been installed the wrong way round the lights won't work.

Do make sure, though, that if using this type of decoder, that it doesn't come into contact with the resistors on the circuit board which it overlaps.

Before replacing the body, program the CV settings as required on the programming track and test the loco on the main line or a rolling road. This loco is incorrectly wired and runs in reverse, so if your DCC command system doesn't allow you to define which way the loco should be running when you set the configuration you will need to add 1 to whatever the value of CV29 is in your decoder - remember you can only read CV values on the programming track.


Class 58 with DCC Concepts TS2SAX decoder fitted


If you decide to use another make of decoder make sure it is not too large as there is not much clearance between the circuit board and the roof once the body has been replaced. I attempted to fit both TCS T1 and DCC Concepts D series decoders but I couldn't get the body to clip back correctly into position, so ended up using a DCC Concepts TS2SAX decoder, shown alongside.


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Copyright Bromsgrove Models 2006