Union Mills Class J39 (Original Chassis) DCC Conversion

Mistakes may damage your locomotive, controller or other accessories. Use a multimeter to make absolutely sure you have completely isolated the motor from the track before testing. Always use the Programming Track for testing. Our guides are provided for reference only, and you proceed entirely at your own risk. Unsure about something - try our DCC Conversion Service instead.

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This guide covers the Union Mills Class J39 models with the orignal tender drive chassis arrangement, including:

• Union Mills Class J39 BR Black 64920

The original tender drive has a single shaft motor with several visible cogs on the underside that drive all three axles. The later version uses a dual shaft motor, powering only the outer tender axles - the middle axle is unpowered. For the newer versions of this model, follow the Union Mill Class T9 guide.

There isn't enough room in the tender to fit even the smallest decoder without milling out some of the metal. Rather than do this, this guide takes a somewhat simpler path and hides the decoder in the loco cab instead.

In common with other Union Mills models, one side of the loco has pickups connected to the motor via the black link wire between the loco and tender. The opposite side of the tender has pickups, with the chassis block and motor support making the motor casing live. The motor casing is bridged to one of the motor contacts.

Step 1 - Remove Tender Body

Turn the tender upside down and remove the screw nearest to the loco. The tender body should come off easily.

Step 2 - Rewire Motor

Desolder the wire from the motor, remove the capacitor and the wire that is soldered to the motor housing.

Solder three new black wires to the motor casing, and the two motor contacts. Run these along the side of the tender where the cable exit hole is, then refit the tender body.

You can optionally add a piece of kapton tape over the top of the motor to prevent the casing solder point making contact with the metal body.

As we are using black wires rather than the usual colour-coded ones, you may want to add some temporary labels to them.

Step 3 - Wire Decoder

Solder the three wires to the decoder. Add a short fourth wire for the second track pickup. Strip off more insulation at the other end than usual (about 4mm) and tin it with your soldering iron.

Step 4 - Connect Loco Wire

Insert the end of the loose short black wire into the hole at the back of the loco where the stock wire used to be.

Replace the drawbar and tighten the screw just enough so that it traps the wire in place.

Step 5 - Test

Add a temporary piece of tape over the decoder to protect it, then place the loco on your programming track and read the loco ID. If all is well, remove the temporary tape and replace it with a piece of black heat shrink sleeve.

The decoder can now be tucked away in the cab out of sight, and the conversion is complete.

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