TUTORIAL Repairing 12v points.

[Andromeda]

Anyone been setting up a track and found that they had two left feet? I did the other day, and managed to break my 30 year old points! Lots of swearing ensued, but not all is lost...

The candidates for this topic are my very first set of points(left), and a set that I aquired from 3bay:

In addition to the break, the left set have a poor pass through electrical connection.

First off we need to flip the points over and locate the six plastic rivets. For half of them I just cropped the top off with a pair of wire cutters, The remaining rivets were 'teased' back into a pillar shape using the wire cutters and a pair of pliers - small electrical ones!

On the first picture above, there is what looks like a 7th rivet that perhaps was made too short, larger circled item. It has been chemically welded. Once the first six are free, slip a small screw driver in between where the 7th joins, and gently prise it open. You should hear a snap!

Hear are some pictures of what you get.

For the feint hearted, and those of you who donot have electrical connection issues, the next part can be skipped. All of the ends of my conductor rails had become unwelded from the end braces. If you are feint hearted and do have electrical connection issues, the following two pics try and show you where the contacts are.

Because my points were so old and abused, I continued to prise the central join with a screwdriver like soldering tool. The point is composite, and has been chemically welded during manufacture. Here you can see the weld breaking.

How did this get here? Well now it is, I might as well explain that the melted plastic between the rails was caused by a very bored and destructive 8 year old, exploding button cells!

Here it is, looks remarkably like the 4.5V version! Clever ogeL using the same parts!

These are the broken welds that I mentioned earlier.

You can see the welded middle point. The weld is strong enough to hold while the plastic tears

I checked the continuity and resistance of the conductor rails. One bad connection racked up 15 ohms, whilst most were less than 1 or 2ohms

in the picture pairs 1 and 2 are visible without these last few steps, pair 3 can just be accessed with a screwdriver, without total disassembly.

My trouble was mainly with pair 2, as you can see in the pic they have a little arcing evidence. A small pair of pliers were used to press each metal tab, whilst being pushed/supported from the rail side.

Now to weld the broken base plate. You will need some Methyl ethyl ketone (MEK), a chemical proof crucible/dish and stirrer/applicator, and maybe some broken donor ogeL element of the same colour. I chose to dissolve a very small amount of plastic shavings. Because the break was very clean, I did not really need to additional material.

Add a few drops of MEK and mix with your shavings to your desired consitancy, here it is weak and thin.

Apply sparingly but evenly to the edge of the element to be welded, wait a few seconds then press together. Sometimes applying to both edges. It's best use a flat surface to work on, one prepared with non stick properties, like a strip of kapton tape!

In this example I trimmed the excess too soon, the excess smeared a little. Once it is bonded sufficiently to handle, place on a radiator or somewhere warm to set fully.

Now we are ready to reassemble the points. Get your welding kit together and the parts lined up. We don't need any extra plastic material this time, just a few drops of pure MEK in the crucible. First off we're going to weld the rails in place. Apply MEK as shown and press together, leaving to dry in a warm place again.

Next assemble the base plate and slider. Remember that half rivet that we snapped earlier? Put a spot of MEK on it before lowering the rails onto the base. Try not to push it fully together yet.

Flip the whole unit over and if you have snipped the rivets, place a spot of MEK in each hole, as you've not pushed it fully together right? If you 'teased' the rivets straight, then press together and put a spot of MEK on each, using the end of the pliers press and work the rivet flat. For my snipped rivets, I kept the heads and welded them ontop. The red circles show the snipped rivets, blue the formed ones. Both methods work.

That's it, you've just saved yourself a small fortune!

I'll come back and post about the the RH points later...

[Locomotive Annie]

An excellent repair tutorial Andromeda. None of my 12volt points are broken, but if anything happens to them I now know what to do.

[LEGO Train 12 Volts]

Great work with that broken switch point!

Thanks for sharing Andromeda

[bricks n bolts]

Excellent repair job Andromeda and interesting use of chemicals

How did you test/confirm your bad connections were racking up 15 ohms?

[alainneke]

Very informative! Repairing the rivets with MEK could be useful for 9V points, too. Thanks for sharing!

[Andromeda]

Thanks Guys!

Very informative! Repairing the rivets with MEK could be useful for 9V points, too. Thanks for sharing!

I also use MEK to repair any broken element. It's a bit like solvent weld waste pipe, once you've coated both sides and push together, a very slight twisting helps them bond better. If you've lost the rivet head, just mix more 'donor' plastic into the MEK to make more of 'liquid plastic', this should harden into just plastic!

Excellent repair job Andromeda and interesting use of chemicals

How did you test/confirm your bad connections were racking up 15 ohms?

Using a DVM, or two! I only checked the resistance because the continuity alarm crackled when the point was moved/probed.

I've opened the RH points, pictured very top right, and have found a similar weak connection. Being as these have had less abuse, their welds are quite sturdy. So I may be looking for a less destructive way of better electrical contact under the center old dark grey - perhaps silver conductive paint....

Edit: I did prise the rails off, they were easier than my original point. I'll be looking at them later...

Anyway, these are pics of a straight off connection to the faulty rail on the RH points.

Sanity check second DVM

Applying pressure one way, almost normal readings.

After applying pressure the other way.

Testing the straight through route.

Edited March 1, 2013 by Andromeda

[zephyr1934]

A very nice tutorial, thanks for collecting and sharing so much detail.

[Phoxtane]

While I don't own any 12v track, this MEK stuff sounds like it could come in handy for various applications. Thanks for the tip!