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Installing a Digitrax DZ121 in a Bachmann 44 ton
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
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
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
Phew, plenty of nervous energy expended but a great result.
comments or suggestions from readers; please write