Tomix Thomas the Tank Engine M1 Decoder Installation

 Text and photos submitted by Michael Wong Mahwah, NJ

Installation of TCS M1 decoder in an N-scale Tomix Thomas the Tank Engine


Text Box: Copyright Ė Michael Wong.  Use of any content is prohibited without the consent and authorization of the author.

Disassemble - External

Remove external shell by pressing on the back of Thomas and lifting the back end up.  Once lifted up, the front can be slid out.  Remove deck walkway.  It is held in by four tabs on the frame, two in front and two in back.  This can be tricky as the fit is very precise on the back two tabs.  You may need to use a jewelers screwdriver and pry very gently between frame and walkway.  Do it from a position where if it leave any nicks that it will not be visible.

Remove bottom plate by removing three screws.  The ends of the plates are held in place by four tabs, two on each end.  You need to use a small screwdriver to push the tabs in while gently lifting.  Once the plate is removed, the couplers and springs are exposed.  Removed them and save.

Disassemble - Internal

Remove drive wheels.  Remove the two screws/nuts that hold the frame halves together.  The two halves are ready to separate but you will have to work the two apart as they are partially held together by the plastic motor mount.  Patience and small movements are needed here.  Once the halves are removed, remove the six running gears and the worm drive.  Next remove the motor/motor mount.  Be careful with the tiny tiny springs that connect the motor terminals to the halves for power.  I lost one in a flash.  Although you wonít be needing these itís always good to save small parts that may be needed elsewhere.

Place close attention to the spacer on each screw hole.  Donít lose these.  Also there is some tape where the motor sits to prevent shorts.  On one side of mine there was not enough tape so I added some additional Kapton tape for insulation.  Also, note that a very tiny square piece sits on each lower corner of the frame around the coupler box area.  Make sure you donít accidentally knock these off.  Insulation of the frame is key else you will burn out the decoder.

Prepare Frame

This is where you break out the Dremel to do some minor frame modding.  You will have to grind out some of the frame material around the motor terminals area to prevent shorting.  Some of the space will be taken up by the wires from the decoder so you will want to make some room for them later.  After grinding away the material I place a very small piece of Kapton tape for good measure.  Itís really not need if the gap is big enough.

Since you have the Dremel out, change the tip to a cutter and gently grind off a small area of the powder coat of the frame to allow for the soldering of the power wires of the decoder (more later).

Be sure to clean off all metal shaving by either washing the frame halves or blowing off with compressed air.  You donít want any shorts later on.

Now put a small dab of solder on that area of each frame that you grind/cleaned off (on the outside of the frame).  You will need a minimum 40-watt iron.  You will also need flux to help the solder joint.  Do not spread the solder into a big blob as you will need to heat it up again later to attach the decoder wires.  Remember more solder means more heat needed later on.   A 40-watt ironís heat is barely adequate so donít make the situation worse with a big blob of solder.

Prepare Decoder

The decoder will need to be prepared so it can fit inside the cab of Thomas.  Take a very small scissor or X-Acto knife and trim the excess shrink wrap.  The wrap must be flush with the ends of the decoder board.  Be careful when doing the wire end and avoid cutting any wires!

Take all the unused wires (blue, white, yellow) and trim to form a neat bundle.  I taped my bundle with some Kapton tape.  You can use other tapes.  I just happened to have Kapton lying around.

Prepare Motor

Remove the plastic motor mount.  Use caution as one end slides off in 90 degrees to the other end.  Donít force it as this mount is critical in preventing the motor from touching the frame halves.

Tin the motor terminals.  Use flux to aid in the soldering.  Apparently the material is not very solder friendly but it will eventually take the solder once hot enough.  You WILL melt some of the plastic around it so you need to do this as fast as possible!  I used a 25-watt iron and it still melted the plastic slightly.  You have to tin it else soldering the decoder wires directly without tinning will be next to impossible and youíll probably end up melting more of the plastic motor end. 

Install Decoder

Apply some double-sided tape to the top of the motor and stick the decoder on.  The decoder has to sit on the forward end of the motor towards the flywheel.

[Note: the pictures show the decoder sitting too far forward.  It wasnít until I assembled it later that I realized this.  You need to place it more towards the flywheel.]

Next trim the orange and gray wires to length and solder to the terminals.  Again be quick with  the soldering iron!  The orange is positive and the gray is negative.  Donít worry about wire lengths being slightly too long.  Thereís enough space in Thomasí cab to absorb any extra.

Assemble Internal

Now you are ready to partially put Thomas back together again.  Reinstall the plastic motor mount.  Leave the red and black wires of the decoder sticking out.  Install the motor/motor mount assembly, the worm gear, and the other six drive gears.  At this time you may want to remove any excess grease and re-lube with light oil.  Assemble the two halves together making sure the spacers are between the halves.

Before moving to the next step, test the decoder and your assembly.  Connect the red and black wire to a DC source around 6 volts.  You can use a DC power pack and increase the throttle slowly.  The decoder can take DC input without re-programming.  Make sure the mechanism runs quiet and without binding.  You may have to fiddle with the tightness of how the two halves are held together or jiggle the motor so everything meshes properly.  I didnít do this step and found out later after everything was re-assembled and soldered that it had a grinding noise!  Yes, I had to disassemble almost everything to get rid of the noise.  During the second time I got it run as quiet and as smooth as any of my best engines.

Final Wiring

At this point you should have a very fine running mechanism.  Trim the red and black wires and solder to the sides of the frame halves.  Some hints on what to watch out for here.  This is the only way I could figure out how to attach the power leads of the decoder.  The older versions of Thomas had plenty of room and location but with this new and current design, Thomas is designed and built like modern day N-scale locomotives Ė split frame design.  This leaves very little room for wire placement and attachment.  It just happens to be that the area around the motor there is a gap between the frame and shell that a decoder wire can fit through.  Route the wires as shown and you wonít have any clearance problems.  Donít worry about wire lengths being slightly too long.  Thereís enough space in Thomasí cab to absorb any extra.

Again with the soldering you need to do it quick else the frame will absorb all the heat and potentially melt the internal plastic gears.  What I did was place a decoder lead on the solder ďpadĒ created earlier and apply the iron until things start to flow a little.  You will not get complete flow as a 40-watt iron will not be hot enough to do that.  Donít worry about the heat traveling up the wires as the wires are thin and long enough to prevent too much heat from traveling up.  Once thereís some flow near the wire, stop.  Check to make sure itís not a cold solder joint.

Once done make sure thereís no excess solder sticking up or it will interfere with the shell re-assembly later on.  You can file it down if thereís too much solder.

Clean the joint to get rid of the flux.

Assemble External

Install the drive wheel linkage by lining up the square bronze bearings.  Install the center drive wheel the same way but make sure it is oriented correctly so the connecting rod appears to be connected to it (itís not).  If done right the hole where the connecting rod should be connected will be hidden by the connecting rod itself.

Assemble the springs and couplers and snap back the bottom plate.  Do not install the screws at this time.  As a side note, thereís nothing on my layout that uses Rapido couplers so I exchanged them for Unimate (knuckle) couplers made by Red Caboose.  They come in three sizes (short, medium, long).  The long size is the best fit.  A pack of eight runs about $2.50.  I also changed out Annie and Clarabelís couplers.  Now I can use Thomas to pull any of my rolling stock.  Note that you will have to file down the ďthicknessĒ of the couple or it will bind.  Compare the Unimates to the Rapidos.

Test run Thomas.  It should still be as smooth.  Install the three screws and tighten.  In my situation, as soon as any of the three screws start to tighten a little it would bind the gears causing noise and jerky motion.  I needed to back all three to the point where they are loose.  To solve the problem of potential screw loss I put a touch of Loctite on each screw.  Once cured, you can still adjust the screws to the point of just before binding.  The Loctite will prevent the screws from further rattling loose.

Program the Decoder

Program the decoder to the address of your choice.  I used ď1Ē as that is Thomasí number.  A note on performance, due to Thomasí small size and small drive train I had to play with the Dithering feature of the M1 to allow Thomas to run at very very slow speeds.  I find CV57 set to 40 does the trick.  CV56 can be left at the factory default of 3.

Happy running!


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