Installing a DCC decoder in a Hornby Class 423 VEP Unit
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This page was last updated 31 March, 2020
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 it is one of the most straightforward decoder installations. The decoder socket is located in the MBSO trailer car rather than in either of the end DTCL units. In order to control the lighting in the 4-car set a 4-function decoder is required. In fact any 4-function decoder of choice with an 8-pin plug would suit (EXCEPT the DCC Concepts DP4SAX or DP4SAP decoders as they are too long to fit across the carriage roof) as there is plenty of room inside the model.
Removing the body is not really difficult, just a little frustrating! It is easiest to run a finger nail along one side of the body from the mid-point to one end, then do the same the other side to try to release the same end. It isn't possible to move the body very far and found that it frequently drops back and locks itself again to the chassis!! Some models are easier to release the body on than others. Persevere, as it will eventually come apart but handle gently so as not to damage any of the glazing or fine undergear detailing.
Once the body has been separated a little you will find that the lighting PCB has a flying lead attached to it. The lead is not very long, so you are advised to detach it from the board. The easiest way of doing this is with the tool that Hornby has released for this specific purpose.. The tool is not only extremely useful for extracting this type of connector but also for extracting decoders from sockets!
Once the body has been removed you should be able to identify the rather large blanking plug, located in the roof of the model. Remove it gently (using the extraction tool, if to hand) and it is then obvious where the 8-pin plug on the decoder will go.
Pin 1 (orange wire) is clearly identified on the circuit board in the model by a large white triangle.
Almost any size OO/HO 4-function decoder will fit as there is plenty of space inside, so a suitable decoder would be the TCS T4X-MH, DCC Concepts S4SAX or, as used here, the DCC Concepts TS4SAX (shown alongside and below).
Once installed, replace the lighting cable and test that the decoder operates the motor and lighting correctly.
Lighting is controlled as follows:
F0 controls exterior lights front and rear (when the complete unit is assembled in the correct order*)
F1 controls interior lights (these can be tested just in the motor car before reassembly)
One word of warning - before refitting the body check to make sure that the lighting cable between chassis and body folds AWAY from the capacitor on the roof circuit board otherwise you risk heat from the capacitor melting the lighting loom - voice of experience!
*In order for the internal lights to work across all carriages the 4-car sets need to be connected in the right order, as below:
BR Blue - 76441 - 62217 - 70907 - 76442
NSE - 76923 - 62467 - 71146 - 76924
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