HARDER & STEENBECK
With the upturned model held securely, work started by removing the body, as per the Heljan instruction sheet. The front pony truck, which doesn’t feature power collection, was removed first.
The circuit board and decoder socket are held in slots in the chassis block and can be pulled out gently with tweezers. The Zimo M649N chip is much longer than the slot, so the PCB must be moved into the cab.
I wrapped the decoder in insulation tape before slotting it into the locomotive’s circuit board, to avoid short circuits. Black Tack holds the circuit boards in place within the cab, with the re-routed cables also held with Black Tack.
The right-hand corner of the backhead was cut away to allow the cables to run into the cab and provide clearance for the decoder. A few test runs were required, to check that the boiler and cab sections would fit correctly.
The rear pony truck also needs to be removed to provide access to the rear body mounting screws. Take care not to damage the power cables, one of which had already come adrift on George’s model – this would be fixed later.
To allow the Zimo decoder to fit into the cab interior, the six pins were gently bent to a 90º angle with fine-nose pliers. Care must be taken not to put stress on the soldered bonds with the circuit board, so be gentle!
The two wires from the sound decoder were shortened slightly before being soldered to the tags on the Zimo sugar cube speaker. The speaker will be fixed to the inside of the cab roof with Black Tack, which is extremely sticky.
After reattaching the body to the chassis, the loose cable was soldered to the rear pony truck before the model was tested thoroughly.
The front mounting screw releases the smokebox assembly, while the other two screws secure the cab and main boiler section. Place the screws and any loose parts into a lidded container for safe keeping.
To ensure a snug fit with the decoder socket, the pins were shortened by approximately 3mm with a set of good quality, sharp metal cutting shears. Take care not to deform the pins excessively.