I'm using for the first time the new tiny decoder from Doehler&Haass PD05A. I bought it to my regular supplier of DCC equipment DECODERS.ES
This Kato model is similar to all electric locomotives, with a light board (led lighted) that takes the current from the tracks and also feeds motor:
All decoder connections will be done to the board, except for the motor. Motor plates are at board level, so there is no need to disassemble the locomotive body.
First of all you have to identify which side of the led is the positive and which is the negative. This is very easy to find out using a tester in the position "diode testing" (that one that beeps when shorted). If you put the red tip in the positive side of the led and black one in the negative, led will light slightly. If you touch the led in the reversed polarity nothing will be harmed, and led will not light.
Positive side of led must remain connected to rail current (this decoder has no blue wire). Negative side must be isolated and connected to white and yellow wire.
In the following schema you can see the positive and negative side of each led, where I decided to cut the cooper track to isolate negative sides (yellow arrow), and where I decided to cut the cooper track to solder the needed SMD resistor (1kOhm in my case):
Next photo shows where to solder each of the decoder wires after removing the capacitor and resistor that board already has. There is also a bridge or jumper to do in the place of the old resistor:
With this board preparation you can solder decoder wires. Lift the motor plates and make sure they are well isolated, and not touching any other cooper track. You can put some kapton tape arround it for extra security:
If you find there is not enough room to close the frame, you can cut it as on the top of it there is the gray roof giving you more space for your decoder and wires:
And everything is ready to test!! I hope this mini-tutorial was useful.