Classic UK Minitrix Models  -  DCC
Fitting a Chip

Forget silicon, the new balsa wood dcc chip is much cheaper. Its one drawback is that it doesn't work. A mockup, prior to purchase to verify that the chip will fit inside the locos.

The Gaugemaster DCC22. A very tiny DCC controller for N Gauge. 11mm x 9mm. The Lenz Silver Mini is about the smae size.

 



I attempted to fit the chip inside the tender, but the bulk of the 4 wires and the connections and insulation made routing of the wires difficult.

Instead, a removed sections of the boiler weight.

I used a hacksaw, a Stanley knife, a grinding wheel and a steel file. The knife is very effective at shaving the soft metal.



Testing the fit.

The chip rests on the metal weight and against the inside of the boiler.

Strips ofcard provide a 'shelf' to prevent the chip dropping down onto the wheels.

Insulation taper to preven shorting. Note the rear of the weight may need taping too, it may run close to the copper pickup strips which rise to the small circuit board between the motor and the boiler weight.

The original wiring. Carefully remove the motor brush caps slowly to prevent the spring from jumping out. Desolder the vertical copper strips from the left hand end in this photo.

Unscrew the screw which provides a connection between the left wheels and the chassis. lift off the circuit board.

Unsolder and remove completely the capacitor (under the board) and the choke coil. It is unlikely that these will come off easily. You wont be re-using them though. Clean up the soldered contacts and apply a new blob of solder to the front two joints where the pickup strips will be connected.

Re-secure the circuit baord, and re-solder the two copper pickup strips. You may need to hold the strip down as the solder cools. The black lead needs to be re-soldered to the right hand (far side in the picture) joint. Be prepared for the pickup strip to spring free !

 

 

A brief word about what we are doing here. With normal analogue control, the train picks up the current from the track and feeds it direct to the motor. The amount of power supplied to the track determines the speed of the motor.

With DCC, the chip is the thing that is wired to the pickups, and the voltage supplied to the track is constant. It is always on no matter whether the train is moving or stationary. The chip decides how much power to send to the motor, based on signals it receives through the pickups from the controller.

So, the motor should be isolated from the track completely. In the case of the 9F it is easy. The left hand side pickups are connected to the chassis by the screw in the circuit board. The motor is connected to the chassis by the sprung tab on the cap for the bottom motor brush. Remove this tab, and the motor is isolated.

So we need two wires from the DCC chip to the motor. Another 2 wires from the DCC chip to the wheel pickups. But not just any two. DCC chips have colour coded wires. You have to select the correct ones.

So here it is wired in. Leads deliberately left a tad long. Better long than too short !

After writing this, the red lead broke from the circuit board,and the grey ead broke from the brush cap. The grey lead was easy, I had left enough length spare to re-strip and re-solder. I successfully resoldered the red lead using a ground down solder tip. I tinned the tip and cleaned off all surplus solder. I taped the chip onto some tissue paper which I soaked in water, and pressed the chip down so that the underside circuits components were wet. I tinned the red lead, and held it in place over the tiny blob on the board. Watching with a magnifying glass, I lightly touched the wire with the fine soldering iron tip until I could see the blob underneath melt, and then removed the tip and let it cool. The chip takes a while to dry out, but the wtaer had done its job in preventing heat from damaging the tiny components.


Close up of the connections to the motor. Grey is the negative lead, orange the positive. With wire this thin, I dont strip the wire with strippers. I melt the plastic at the desired point with the soldering iron. and gently pull the covering off betweeen thumb and finger nails to reveal the bared end. This reduces the risk of breaking the strands to a minimum but the ends look a bit untidy, as seen in this close-up.

Note that the brush cap with the spring is now at the top. This prevents the motor from contacting the chassis.

Note also the correct orientation of the motor. The two indents shown in the picture here should be uppermost.

There are two tabs that stick out above the middle driving wheel. I have used these to connect the red (right) and black (left) leads to the DCC chip.


The chip in place. Mine rests against the boiler weight, supported by the thin strips of card - these need to be painted black because they can be seen below the boiler body. A strip of insulation tape is wrapped around the wires, which effectively holds the chip in place. The Yellow, Blue and White leads are for front and rear lights, which I haven't bothered to wire in - mainly because the light uses the chassis. So does the left side pickups and the connection to the tender. There is room above the motor to accomodate the loose ends. Note the card / black tape cover over the motor to ensure that the wires do not get rubbed by the worm gear

An here it is assembled again. Note the need to paint the white card support, black. Note also, the chip has dropped. It was after this photo that I went back and put in place the card 'shelf'. ! The red wire also needs to be tucked out of sight.

Maintaining Classic UK Minitrix Locos
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