Hornby class 31 - Fixing broken pickup wires

19 July 2024

7 min Class 31 (British) Electronics

Introduction Tools Detaching the bogie Soldering on new wires Putting the engine together

Introduction

Model of the Class 31 parked at a siding on a carpet layout.

I have a Hornby Class 31 in my collection. Recently I noticed poor performance for the engine. It stopped on basically every single turnout and sometimes even on the straight sections. Cleaning the track and cleaning the wheels didn't help and I also noticed that one of my other trains worked perfectly fine on the same sections.

I therfor deicided to invesigate further. What I did notice when inspecting one of the bogies was that there was some sort of wire hanging loose. You can see the loose wire in the bellow picture.

Two of the axels on the bogie of the model. A broken wire can be seen between two of the axles.

The next step I did was to unscrew the body from the chassis to do some meassurements with a multimeter using the diode test function. There are four screws that I had to unscrew and two cable connectors for the lights that had to be disconnected.

The meassurements where done between the RT terminal and the right hand wheels and between the LT terminal and the left hand wheels. No issues where found with the front bogie, but there where no contact between LT/RT and the rear bogie!

I therfor decided to try to pull both of the wires carefully finding out that both of them where broken :(

The circuit board on the model after loosening it from the shell with it's two broken wires.

So the next step was to detach the bogie from the chassis in order to solder on new wires, as soldering wires on an attached bogie looks imposible.

Tools

I used the following tools for the wire replacement.

Soldering iron (15W, 400 °C)

Solder

Tweezers

Flux, liquid

Tip activator

Soldering brass

Desoldering pump

Soldering stand

Soldering mat

Screwdriver PH1 x 50 mm

Screwdriver flat 2 x 50 mm

Short spirit level

Plier

Servicing cradle

Decoder wire

Solid plastic (19 mm height)

Tip activator is only necessary if you are unable to tin your soldering iron. My soldering iron was fine this time, but I had the tip activator ready in case of problems.

You really do not need the servicing cradle either, as you can just use some packaging you have from some of your locos. I prefer to use a servcing cradle though, since I know my locomotive will be properly protected that way.

The multimeter isn't strictly necessary either, but I personally prefer to use it for testing before I put the loco together.

Detaching the bogie

This was the first time I tried detaching the bogie, so I therefor had to do some Internet searching to find some guidance regarding this. I found this forum thread to be helpfull.

I started by removing the plastic cover above the driver axel. That plastic part is also used to hold the circuit board in place. I also unscrewed the speaker.

Driving axle and it's connection to the bogie.

The next step was to carefully bend the two wings pointing backwards to relase the bogie from the driving axel. The wings should be bent carefully towards the chassis edge. Bellow is a picture of the bogie once the plastic housing is detached.

The driving axel joint after opening up the shell above the bogie.

The bogie can then easly be detached simply by lifting the chassis. I placed a solid piece of plastic with a height of 19 mm bellow the chassis to avoid damage to the coupling while the bogie was detached.

The bogie sitting besides the model after detachment.

Soldering on new wires

I then used my desoldering pump to remove the solder from the bogie terminals.

Close image of the bogie after desoldering wires from terminals between the axels.

The same where done on the LT and RT terminals on the circuit board.

Edge of the model circuit board after desoldering wires.

Then the new wires where pre-tinned and soldered to the bogie terminals. Flux was used to ensure that the solder went where I wanted it. I used Brawa decoder wire 32407 (0,05 mm² rated for 0,5 A). The wire where cutted to aproximately the same length as the old wires, plus some extra slack. The old wires where 60 mm.

I used a regular sized plier to strip the wire. There is no need for a dedicated wire stripper as long as you hold the plier with the flat side away from you and make sure to squeze gently so only the coat is cut. You can also do a gentle jiggle to help loosen the coat.

Close image of the bogie after soldering on new wires to the terimnals located between two of the axels.

I then attached the bogie to the chassis and carefully threaded the cables through their cable holes.

Wires threaded through their respective holes in the chassis.

Then the plastic housing that holds the axel and bogie together where assembled again. Its important to make sure that the plastic housing is properly attached. It should click in place on both sides.

The drive axel joint after adding the plastic housing back.

The plastic mount for the circuit board where then remounted and the circuit board where secured to the chassis again. I then soldered the wires from the bogie to the LT and RT terminals.

New wires soldered to the terminals marked LT and RT on the edge of the circuit board.

I then did some meassurements with my multimeter to verify connectivity. Both of the wires passed the test.

Connectivity test with a multimeter between the wheels and the LT + RT terminals.

Putting the engine together

It was now time for resambly again. That was done by attaching the 4 screws and the two cables. The screws on the rear bogie can be difficult to screw in due to some detailing on the bogie.

Screwdriver screwing a screw underneath the bogie of the model while the bogie is slightly twisted to the side.

I then tested the locomotive. The result was much better performance and no issues over points or at straight sections at lower speeds! It will now be intersting to see how long it will take before I break the wires again.