Micro-Trains GP9

I bought one, since it has a reputation for being a good runner and easy to DCC.

Disassembly:

Pop off the fuel tank. Pull straight down. Remember: the air tanks are towards the rear of the loco. Don advised a black sharpie on the chassis to eliminate the shiny chassis showing though.

Then, with 2 thumbnails, spread the plastic body and the insides will slip out. I do this one end at a time, thumbnail on each body half midpoint, one finger on a truck to pull it loose, turn the loco around and do it again. 

Measure the chassis width, normally 0.330"... the goal is to get it back to factory width after working on it.

Don Fedjur recommends trimming a bit off the 4 lugs that secure the shell to make things easier to remove and replace. I haven't had a problem yet, but if you have difficulty this is a good idea.

Remove the springs on each side. Put your finger over most of the spring, and unhook from the top. The longer loop goes up. Remember: front of loco is end with the springs.

Now you want to remove the circuit board, but note that there is a single post keeping it from sliding forwards. Using a small screwdriver and very light touch lift the end of the board just enough to clear the single post and slide the board off. Be careful, you don't want to break anything.

Adding a TCS decoder:

remove the stock circuit board as above.

loosen three screws on one side only one turn each (use tape flag on your screwdriver shank)

now open up the chassis halves a bit with a flat blade screwdriver, underneath and up top.

measure thickness of the original board near the 4 locations which will engage the 4 pins, should be between 0.033 and 0.035. 

Now inspect the TCS decoder to see if it has the "defect" (a short between the half moons and the motor spring lands) See their site. A defective board will cook itself. New units have the factory mod (a bit of the board ground away to stop the short)

 Now check thickness on the TCS decoder at each of the 4 half moons which are plated, mine were 0.040"

In this case, that means that the TCS is thicker than the original board. If you look carefully at the 4 posts, you can see that the bottom of the slot in each post is actually "stepped", where there is a raised ledge on the bottom half of each post. 

Filing these down a bit, will usually get the slot the right size for the TCS board. You have already measured the stock board, you can check the progress of your "filing" with an auto feeler gauge, or wire gauge.

When all is well, you can put the decoder in place, and slide it a bit into the 4 pins. Once it is in there nicely, then you can tighten the decoder back up (those 3 screws) It should come back to the same thickness overall as it was before you started work. This is to ensure the unit will fit in the shell and come back out again. 

 TCS decoder notes:

Set CV 2 to 0, the geep will crawl at speed step 1 with the lowest start speed. (My NCE PowerCab is about 13 volts to the rails)

 

Digitrax