Farish Class 25 with MX646 hard-wired

Kit: Zimo MX646 (MX649 is direct alternative) with YouChoos SugarCube9 speaker

Strip everything out as we'll be throwing away the factory PCB, grinding the chassis, and hard-wiring everything!

Glue in the mini SMD LEDs for cab lights.

All in pieces and the MX646 decoder and SugarCube7 speaker shown. Use an MX649 decoder nowadays instead, which replaced the MX646, and is smaller, so the install will be even easier!

Speaker will go in the fuel tank, so mark out the section of chassis to grind, being careful not to disturb the screw hole.

After the grinding...

Turns out that we've created enough depth for a SugarCube9 speaker rather than the expected SugarCube7, so test fit with the plastic frame in place... the speaker must sit nearly flush with the lowest plastic point. A neat rectangle will need to be drilled and filed in the bottom of the fuel tank for the speaker to sit in.

Add wires to the speaker and feed through on re-assembly. When you're happy with the fit, fix the speaker into place with a combination of insulating tape, thin double-sided tape and tiny spots of glue so it holds there securely.

With figures added to the cabs, and the cab lights in, wait for the glue there to dry thoroughly (otherwise your windows will mist up!), then place cabs and lighting boards back into palce.

To wire the decoder in, we will re-use parts of the original factory PCB - in particular the screw holes which we'll connect the decoder's red+black pickup wires to, and also the bank or resistors, as we'll need to protect the LEDs when we hard-wire those back in. Note the common side of the resistors that we've soldered a length of thin 'leg' to - this will be the side that the decoder's common positive (blue) wire will connect to.

Insulate the top of the chassis and fix the decoder down loosely with some thin double-sided tape. Our decoder was an 8pin version so we chop off the plug and hard-wire the pickup wires and motor wires (orange+grey) directly.

Be methodical adding the resistor bank in, and wiring up the lighting. It looks complex, but actually is quite straight-forward. Positive side of each LED to the outer-point of a resistor in the bank, and negative of each LED to the appropriate decoder output (white for forward motion lights, yellow for reverse motion lights, green for front cab light and brown for rear cab light).

Protect the joins with heat shrink, tidy up and secure wiring down with tape, adjust the springs that contact to the lighting boards and test everything out. The spring contacts can be tricky to get working reliably, but once on, should remain OK.

So here is the 24 all back together and working nicely, with a lot of sound coming from that SugarCube9 speaker!

Please note that these guides are provided as useful resources for you, as-is. YouChoos cannot be held responsible for errors in the information, or for any damage caused to your models or equipment if you choose to follow any of the steps detailed here.