Classic UK Minitrix Models  -  Black 9F
Motor

Here is a shot of the wiring in a 9F loco that has never had its motor removed. In order to replace brushes, the motor has to be removed. If de-soldering wires, do not apply heat to the caps while the caps are in place. The black housing under the cap is made of plastic. It will melt and destroy the shape which allows the caps to click-lock in place.

 

It is possible to replace the brushes without desoldering. Take off the top cap (gently so that the spring doesn't spring out). Undo the two small screws at the rear of the loco. Rotate the motor so that the green wired cap is accessible. Remove the cap slowly so that the spring doesn't spring out, and tap out the old brush. Fit the new brush and spring, and refit the green wired endcap. Rotate the motor back into position, taking care to allow the spring tag to ease into contact with the chassis. Then fit the new brush and spring under the red wired cap. Refit the screws to hold the motor in place.

The motor unsoldered from its connections and removed from the chassis. Here shown with a brand new set of brushes and springs. The bush housings do not come with the replacement brushes. 40015900 is the correct part number for the 9F and may be still available from German ebay suppliers.

An end-on view. Note the curved caps, the location of the solder and the cap which has a tag folded back on itself. Note the two round indentations in the metal housing. These mark the top - ie, the motor should fit in the chassis with these pointing upwards. And yes, it does matter - if it is placed upside down, the chassis contacts the wrong brush, and the train will run backwards when all the others on your layout run forwards.

A close-up of the work end of the motor, showing the round dents in the casing. Note also the recess into which the metal caps click and lock into place. While in this state, apply a drop of thin oil to the brass bushes where the spindle leaves the casing. The motor should spin rapidly and freely (apart from the slight lumpy feeling caused by the magnets). If it feels rough, it may be that some dirt has got between the casing and the armature. You may see scratch marks on the armature. Spin the motor and blow hard into the motor windings as it spins. Do this a few times to try to clear any debris.

Metal caps with wires soldered into place. Do not solder while the caps are on the motor. The bush housing is plastic and it will melt. Instead, remove the caps, hold them with a crocodile clip or similar and solder the wire into the groove. Ensure that no solder gets onto the inside of the cap - work from the outside. Try the caps in their correct positions without the brushes and springs. The bottom cap is the green wire and this has the tag to make an earth contact with the chassis. Note the method I use for keeping the springs from rolling away !

Inserting the brush housing, the brush (which is quite tiny), and the spring. The cap fits back over the top. Do one at a time to help prevent getting the top and bottom mixed up. Then do the bottom one in the same way. You now have a motor with two leads attached. It would be a shame not to test it.

The motor slots in from the right hand side. Note that I have lightly greased the worm gear - exaggerated by the camera flash. All of the grease is in the bottom of the groove. I also applied a small amount of grease to the teeth of the red gears, and pushed the chassis, without the motor, around the track to distribute the grease. Too much grease here isn't as bad as too much oil, but moderation is still very important. At lest the grease doesn't fly all over the place. I used some silicon grease I had lying around.

The motor in position from the left side. The circuit board is held up by the ends of the brass pickups at the moment.


The circuit board in position. I have cut the wires much longer than the original, which makes things look rather untidy. But in order to replace the brushes, I had to unsolder the wires from the motor. Leaving the wires long, allows the motor to be taken out without de-soldering.

Note the two brass strips which run vertically from the wheel pickups to the circuit board. Be careful when soldering that the ends of theses strips do not spring out from the molten solder.

Minitrix® and Trix® are tradenames currently owned by Märklin Inc.

(c) 2011 JF Heath

Maintaining Classic UK Minitrix Locos
The Minitrix trademark is currently owned by Märklin Inc.  Gebr. Märklin & Cie. GmbH, Stuttgarter Straβe 55-57, D-73033 Göppingen, Baden-Württemberg

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