Installing a DCC decoder in a Heljan Class 15 Diesel Loco

Click on each image for a more detailed view

Class 15

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.

Note that this loco will not negotiate tight curves.

The first step in installing a decoder in this loco is totally ignore the fitting instructions provided by Heljan. If you do, you risk damaging the loco as the cab does NOT come off easily, if at all!! It actually seems to be glued in place.

You will need two small screwdrivers, one with a flat end and one Phillips type.

Class 15 - removing screws


First, remove the battery box located in the centre of the underframe.

Then undo the two small cross-head screws which fix the body to the chassis. Be careful - these screws are very small and can easily get lost. The best place for them is in the battery box you have just removed.

The next task is to separate the body and chassis - not easy and requires some patience as the body is an extremely tight fit!

With a finger nail gently prise the body away from the chassis on one side first, then the other, working the front end away from the chassis first. It is possible to get a small flat headed screwdriver between the body and chassis right at the very end of the chassis, both front and rear, to gently lever the two apart.


Class 15 - body removed


Class 15 - DCC socket

Class 15 - decoder installed

Class 15 with DP2X decoder Class 15 with DP2X decoder



Once inside remove the dummy plug from the decoder socket. Be careful that you do not damage any of the small wires surrounding the plug (or even going over it on some models).







Pin 1 is then clearly marked.







This installation shows a TCS DP2X-UK decoder being fitted. It does just fit, allowing the body to be replaced, even though there is a very slight overhang on one edge. This decoder is ideal as it has no wires but there is plenty of space inside for any type of decoder. The TCS DP2X is a better option as the pins are aligned across the decoder rather than along it, but it hasn't been possible to test this option as there wasn't one to hand. (It has now been possible to install a DP2X - see bottom photo.) With a wired decoder it would be advisable to provide a ledge across the chassis over the front bogie for the decoder to be fixed to.


Program the decoder as required BEFORE replacing the body and check that everything works as expected. On this example the motor was a little jerky at slow speed. Removing the capacitor improved the running slightly, but trying an alternative decoder (Zimo MX630R) made no difference (either with or without the capacitor in place). Running in the loco on a rolling road did improve its slow running qualities.


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