Graham Farish N gauge Class 47 diesel with MX660 drop-in sound

Kit: MX660; SugarCurve6; SACC16 + 2x Tall 470uF Tantalums

The usual 6pin socket PCB comes in this Class 47, which we take out completely. Solder orange and grey wires to the motor contacts directly - got to be especially careful here as the terminals are very close to the chassis, so must not bridge.

A layer of electrical tape on the chassis to protect the decoder, followed by thin double-sided tape, then the MX660 sits on top.

The screw eyelets are cut from the original factory PCB, to which we solder the red and black pickup wires to the decoder.

Electrical tape, followed by double-sided tape again for the SugarCurve6 speaker. No need to modify the chassis - the body fits on happily with this speaker.

Now for the tricky bit... the lighting. Farish produce numerous versions of lighting boards for the Class 47 - some with 2 red tail lights, others with head-code, and others with markers. This is the most complex one - a single red light, a single white marker light, and a yellow light for the head lights - at each end.

We remove the short rigid wires from the lighting boards anyway, and rewire with some finer, more flexible decoder wire, and work out which connection is which - the blues are all positives, connection 'D' is for the white+yellow lights and 'B' is for the red light. Red is easy, as it is a single light, but white+yellow is more difficult - they have separate positive wires, but a shared ground, which is fine on the original Farish PCB where the protective resistors are on the positive side, but the MX660 provides reduced-voltage ground outputs, effectively the resistor being on the ground side, so this isn't going to work - we'll only get the white or the yellow to come on (not both) as the voltage ratings are different and sharing a resistor won't work.

We try it out anyway, and sure enough, we get control of the red and yellow, but the white LED won't come on.

The only solution, if we want control of the white LED too, is to modify the lighting PCB circuit, effectively cutting off the ground input to it, and using a different aux output of the decoder especially for it. Luckily the PCB is easy to read and we can see exactly which track needs to be severed. We begin by scoring it, but the cut has to go deep, so we end up actually drilling an air-gap all the way through the PCB. The green wire is added directly to the ground/negative side of the white LED.

The new green wire is connected to the MX660's remaining outputs - FA2 at the front and FA4 at the rear. There are no more outputs remaining, so we've no way to add cab lights to this model.

A SACC16 PCB is snipped, and 2x 470uF Tall Tantalums are wired on for stay-alive... there is enouhg room at the opposite end to the speaker for this to sit, protected with Kapton tape. The SACC16 is mounted above the MX660.

Back together, and we have independent control of the yellow head lights, the white markers and the red tail lights... and sound with stay-alive too of course!

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