Fixing a Brio electric locomotive

Favourite electric engine number 7 started working only intermittently. Electrical fault? Carpet fluff in the gears? This photo blog details how I fixed it.

Three evil triangular screws.

First I asked the internet for help on getting the thing open. The base of the locomotive is held on with triangular-headed screws, and to my astonishment I learned that no tools are sold that deal with these screws. The entire comprehensive wikipedia article on all screw types doesn't have a single plain equilateral triangular driver listed. I find this most surprising, since I could imagine a strong case being made that a triangular hole is ideal (compared with the widely-used hex-key, which is much more prone to stripping than a triangle-key would be). I hoped that one of hex keys might fit snugly in the triangle and do the job, but even my very smallest hex key was too large.
This page describes how to grind an allen key into a triangular shape, and suggests that the problem with the engine might be fluff-in-gears.
In the comments on this page, someone said "A Torx T-7 screwdriver worked just great for me", so I hunted out my never-used what-are-these-things-for-anyway T-* drivers, and found I had several T-20, several T-15, and several T-10... but no T-7.
Uncle Davin came to the rescue and bought a lovely set of tiny drivers, including a T-7... which didn't fit, and a T-5, which did fit perfectly.

[Incidentally, woodenrailway.info looked like a promising site for this topic, but I couldn't find any help there on this particular engine.]

As I opened the base, one of the magnets fell off, then the second magnet went slurp-clunk into the inside and out clattered an embarrassing and incomprehensible array of little metal slabs. Where did they come from? What a mess! (Lesson number one: don't take it apart upside-down: right-way up would be much better! And then expect the drive wheel to come up with the top, and leave behind the other two wheels in the base, along with the two magnets.) 

I cleaned a little bit of tangled fluff off the main axle with tweezers. There didn't seem to be any fluff in the gears.

After a lot of testing of the motor, I tracked down the intermittent fault to the tiny green-buttoned cut-out switch (the green button of which normally protrudes through the base of the engine).  I tried to scratch up this switch's surfaces to restore it to health, but no matter what I did, the switch remained niggly. How useless, given how expensive this engine was, and it is only one year old! 

I decided that major corrective surgery was the only solution. I snipped out the switch altogether, stripped the wires, and connected them together.  

Then it was time to figure out how to re-assemble, in particular, what to do with the three loose metal plates. After a few false starts I arrived at this hypothesis for where the three plates go -- they are the bright silver bits to the south and north of the central axle.  

Also shown is the lego block on which I placed the base and wheels before attempting to put it together. (Otherwise the axles would be in the way.)

Here we are, ready to go, with the last magnet slipping in place (tweezers were required to get the magnet detached from its own little bolt).  I've replaced the little green button in its correct location, even though it is now not connected to anything. For the next step, a firm hand was required to keep the drive wheels and gears in the right place, and I relied on friction to keep the vestigial green button on its two little stalks. 

I held the wheels very firmly and slid everything together, making sure the supporting lego piece was not obstructing the hole that the green button needs to protrude out of. 

Success! All screwed together, and displayed alongside the tools that did the job.