Classic UK Minitrix Models  -  Lower Circuit Board
and some electrical info

The lower circuit board takes the electrical pickup from the track, cuts out the electrical interference from the motor and distributes the power to the motor and to the lights.  It contains a small choke coil (which cuts out high frequencies) and a capacitor which effectively reduces the lower frequency noises.

As with many of the Minitrix models, there is no pickup brush for the left (negative) side.  The wheel flange is connected electrically to the axle.  The axle runs in a brass bush and the bush is in direct contact with the chassis.  On most minitrix models, the chassis is therefore connected to the left side rail.  The pickup for the right rail is through the copper contact strips which press against the inside face of the right wheel.  This wheel must be isolated electrically from the axle, and in the case of many Minitrix models this is achieved by placing a sleeve between the axle and the wheel.

At first glance the axles may look symmetrical, but they are not. They have a left wheel and a right wheel.  Usually, when the loco is running forwards, positive is on the right, negative is on the left.  The chassis is negative.  The Warship does not follow this rule for some reason, but when assembling, we can assume that it does until much later.

The motor sits on top of the lower circuit board and makes direct contact (no wires) with the copper tabs which stick up from the circuit board.

A flash back to the disassembly.  Knowing which is front and which is rear is important on every other Minitrix diesel I have worked on.  It is less of an issue with this Class 42 Warship, but I am going to follow the same process.  Look at the photo of the rear of the chassis.  The screw holding the gear cover in place is on the side closest to you.  Front is to the left, rear is to the right.  Position your chassis in the same orientation.
Keep the chassis handy, but prepare the lower circuit board and the plastic undertray.  Just to confuse you, this is the wrong way round.  The two copper tags should be at the rear.  Notice how the slots in the side of the circuit board locate the plastic uprights of the undertray.

Also (and this is the reason for the photo being taken from this side) note how the copper on the nearest tab wraps around the side of the circuit board.  It doesn't do this on the other side.  Why is this, I wonder ?   Well - that bit of copper is the only contact between the negative side pickups (through the wheels and axle to the chassis) and the motor.  It needs to be clean and the inside of the loco chassis where it contacts also needs to be clean.  Having checked this, turn it round and place the assembly next to the chassis.

Thread the upper circuit board through the chassis from the underside, and gently insert the undertray assembly.  Be very careful with those plastic uprights - guide them into place and don't force the undertray into position - guide it into place.  Note the lip half way down the inside of the chassis against which the circuit board rests.  The plastic arms may snag against them.
This is what we are aiming for, viewed from the top.  The copper strips at the rear (right of photo) of the loco.  The black plastic arms of the undertray butt against the side mouldings at the front (far side of photo) and the rear (near side of photo).  When fully inserted, they 'latch' over the top of the this sidewall of the chassis.  It is a very fragile arrangement for such an important component.  Note also how that copper strip on the tag on circuit board at the farside of the photo makes contact with the chassis wall.  If that connection is not good, the motor will not run.

The red wire connecting to the upper circuit board is going to be in the way for a while.  Try not to flex it around too much - you don't want the connection to the circuit board to break.

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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