Classic UK Minitrix Models  -  Fitting DCC
To the Class 112

Fitting a DCC chip to this loco is not that difficult.  I made it a bit more awkward by opting to fit a 6 pin plug with a separate harness and socket.  This makes the chip about twice as long as it would be if I had just purchased a version with wires already attached - but infinitely more difficult to replace the chip in the event of a failure. 

 

Of course, when fitting any DCC chip you must first make absolutely certain that the loco is running perfectly well on DC.  Here, I had taken two wires from the motor and two wires from the pickups.  These connections should come from the lower circuit board, but in practice I found it impossible to ensure that the connections were reliable.  In the end, I resorted to soldering the wires onto the motor tags (blue and green in the photo), and positive wire from the lower circuit board sweep track (red wire in the photo)

I fashioned a separate earth contact from the screw which holds the worm gear cover in place.  This can be seen clearly in this photo with the green wire wrapped crudely and temporarily around the left hand side.  The bend in the brass tag is wide enough to allow the circuit board to slot into, and the circuit board has a little notch filed out.    Note the insulating tape to make sure that the brass strip does not make contact with anything on the underside of the upper circuit board.  I also placed a small upward bend to make sure that the top of the worm gear does not catch.

The wire is very thin - I have not been able to source it, but this comes from the screened multi-core cable that is used for wiring up such things as 5-Pin DIN plugs for audio purposes.  For some reason I have a drum of it in the garage.  Handy.

As a final electrical test I connected the bare ends of the pairs of wires together.  The two green ones and the red and blue ones.  This fed the power from the pickups to the motor.  I ran it round the track like this with the wires trailing to make sure that the loco was running properly in both directions, and also that I had the polarity of the wiring to the motor correct.  It is normal for the pickups on the wheels to be on the right hand side of the train when it is moving forwards.

Here showing the upper circuit board in place, held down with the screws that are used to hold the metal body in position.

Note the insulation tape around the board at the right hand end, and the home made brass tab folded over the edge of the board.

Ignore the colours - these are just what I had available, and nothing to do with the colour coding used for wiring in the DCC chip.  I am just bringing the wires from the lower circuit board to a location on the upper.  The blue and green from the motor are soldered onto separate larger areas originally used for the selenium diode.  The red wire from the +ve (right) rail pickup is soldered onto the track which is connected to the upwardly sprung tabs for the pantograph connection.

Here positioning the chip and harness, and taping it down into a location that looks as though it might work.  In fact, at this stage, I know it works.  I tried this before ever starting to solder anything.  The chip is insulated (an advantage of the DCC22).  The tape is there to hold it in place.  Normally, I would use a double sided sellotape tab, but there isn't enough clearance in the roof for this.  In this position, the chip itself fits into the well formed by the raised section of the roof.  The black shrouded 6 pin socket doesn't fit, but manages to squeeze itself under the flatter part of the roof.

Note the position of the screws.  The chip and the wires must keep clear of these.

The next step is to cut the wires of the chip holder and solder them into place. 
Red and Black for Right and Left side pickups.
Orange and Grey for +ve and -ve motor connections
Yellow and White for Reverse and Forward lights. In fact, wired the wrong way round on this photo, as I discovered later - not sure how that happened, but I had to interchange the yellow and white wires.

And a shot from above.  Once more, I ran the loco around the track with the chip in this position for some time, ensuring that all was working correctly.  It was at this point that I discovered the yellow and white wires were not soldered correctly.

The top fits into place with a bit of gentle persuasion.  No force, more a case of easing everything into position, and making absolutely certain thet the coloured wires do not get trapped under the moulding for the screw holes.  Almost impossible without applying more thin strips of tape.

Maintaining Classic UK Minitrix Locos
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