Installing a Digitrax DZ121 in a Bachmann 44 ton loco.

By Ernest Puddick

I have fitted a DZ121 into a Bachmann 44 tonner. This was combined with a project to lower the body on the frame (It sits a little high).

The first job was to remove all screws to separate the main components. The wires from the trucks are unsoldered from the PCB.

The lowering is achieved by using a hack saw to remove material from on top of the tanks where the body fixing screws are located. Enough material should be removed to let the body sit on the 4 rectangular 'bumps' on top of the frame. The amount of space on top of the frame is reduced. The next job is to remove all components from the PCB. The bulbs will be reused later. Reduce the PCB by 7 mm at each end. The copper strip is then cut at several points to produce pads for soldering the lights (2 at each end), the motor leads (2 on each side) and the track power (2 on each side).

The DZ121 has leads that can be shortened to provide a supply of fine flexible wire.

On each truck remove the 4 screws from the top and lift off the upper frame to release the motors. Solder a piece of wire to each brush holder. With some fine scissors cut off the sections of pick up that originally fed track power to the motors. Pop the motors back in position and feed the wires up through the two holes in the upper frame, these were not used before but are very convenient to keep the motor wires neat. Replace the 4 screws and check the motors turn over freely.

Replace the trucks under the frame, ensuring the screws are not too tight, and then screw the PCB back into position, including the insulating sheet underneath.

It's now time to start soldering the DZ121 into position.

First cut the leads on the bulbs to half their original length and solder back into position. The bulbs must sit into the recesses, on the frame, with nothing protruding beyond the ends of the frame. Decide on which end is to be the front and solder the white, yellow and blue wires accordingly. The spare section of blue being used to jump the 'lighting return' from one end of the PCB to the other.

Next solder the track power leads from the trucks and the red and black wires to the PCB. Again refer to the front of the unit (Red to right rule applies).

The decoder can then be tested for lights only.

If all's well the motor leads and the gray and orange wires can be soldered to the PCB. Tip; check that the motor leads are the correct orientation by testing with a DC analogue supply, to make sure that both trucks go in the right direction!

The unit can then be track tested for operation. I was really pleased with the running of the unit. As yet I have not enabled the BEMF function.

Finally fitting the body. I removed the tabs from under the body that held the cab in position. Then you can ease the handrails out of the cab enabling it to slide up and off. I removed the brakeman's seat and the plastic moulding below. This is where the DZ121 will sit. It is then possible to fit the body only and ensure that it sits correctly on the frame with no wires trapped. Screw in the two body fixing screws. Slide the DZ121 down into the pocket where the brakeman's seat used to be. After a final track test the wires visible in the cab area can be taped down and the cab fitted back into position.

Phew, plenty of nervous energy expended but a great result.

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