Every railway should have one! This is the Tomix model and it looks the part. Instantly recognisable, and usually popular, Thomas fits in with a railway of any era. I saw the advert and had to have one!I was expecting adding a decoder to be quite easy, having read a description of chipping on the web somewhere. However after removing the body it was clear there have been some design changes! Thomas is now based upon a split frame chassis, and surgery would be required.
The body removed easily by squeezing at the front and rear: that releases two plastic catches and the body separates at the footplate. The footplate itself then lifts off once it clears some indentations (this should be obvious). At that point you are left with a split frame chassis.
Flip it upside down, remove the three screws and put them in a safe place. The plastic base is clipped at either end near the couplings: the clips can be released using the end of a pair of tweezers at the sides. Lift it off carefully and put it in the safe place. Lift out the couplings and springs carefully, and add them to the safe place. the view will then be like this. Then the wheels can be lifted out.
Undo the two screws at the side and the two halves can be prised apart. The motor contacts are connected to the chassis using two tiny springs. you need not put these into the safe place, as they won't be needed (but they look to me very useful for something!)
The decoder installation requires connection to the motor (easy, now we can get at the terminals) and connection to the chassis. The only route I could see for that was to solder to the chassis itself. So:
- file away the "bump" where the springs used to attach (red circle);
- Tin the chassis at a convenient point (red square).
Here's the chassis ready to go back together, with the spacers in place. I forgot to say - be very careful with the gears!
"Reassembly is the reverse of disassembly". Join the 2 chassis sides together: take care to get the plastic spacers around the motor's worm gear the right way around. Then replace the screws holding the chassis side together, and breathe a sign of relief. With the wheels in place, put back the coupling and spring carefully and clip back on the plastic base; then add the 3 screws.
The wheels are quite simple to put in place and quite hard to get the "quartering" right. Because each axle is driven, but the end axles are joined by the connecting rods, it is important to get the end two axles onto the correct gear "tooth". If this is wrong, he will lurch along and it will be necessary to undo the plastic base, lift out an end axle and reinsert it with it turned round slightly so it engages on the next gear tooth.
When the wheels are driven by the "right" gear tooth, he runs smoothly. Don't worry: you will be able to solve this. Run the chassis, and see if the connecting rod doesn't look quite level. Move the front wheel till it ends up right.
I soldered the decoder on after reassembling the chassis. I have an 80W temperature controlled iron, so getting enough heat into the chassis isn't hard. The decoder sits in the top of the cab visible through the windows. The connections to the motor are easy to solder.
And that's it - not so hard after all to do these split frame chassis locos!
Initially I got a lot of track shorts on Digitrax PM42 power managers. I then spotted that only some PM42 zones did this, and a subsequent activity to "balance" the trip currents made the problem go away.