This installation of the TCS AS6 Decoder is for HO Scale Atlas S1, S2, S3, and S4 Switcher and was performed by TCS
First remove the cab shell by spreading it on either side and lifting it up and off. Next remove the long hood by tipping it forward and lifting it off, taking care not to to damage the front plastic clip that holds the shell on the frame.
Now you should be presented with a locomotive that looks like the one above. Desolder the four wires from the lighting board and your locomotive will look like the image below.
Next, remove the screw highlighted below and lift the lighting board followed by the weight.
With the weight removed apply kapton tape to the four spots identified in the image below. This is necessary to ensure electrical insulation between the motor and the frame.
Next, flip the locomotive upside and identify the screw highlighted in red below.
Remove this screw and set it to the side (we will be replacing it with a nylon screw).
Place the locomotive right-side up again and remove the motor by lifting it straight out.
Now, apply kapton tape to the frame where the motor sits. Note that in the image below a small hole has been poked in the kapton tape to allow the nylon screw to pass through.
Replace the motor (taking care to line up the drive shafts), tighten it in place with a nylon screw through the bottom of the frame, replace the weight, and screw on the AS6 decoder as seen below.
Lastly, solder the four track pickup wires to the four corresponding pads on the AS6 and press down on the back of the board while taping it down as shown to ensure a strong electrical connection with the motor. Your locomotive should look like the image below and be ready for the shell to be put back on and run. Notice the extra four gold pads (shown in the lower right corner of the AS6) which provide 4 additional functions for LED light. The current limit resistors are on board so no additional or external resistors are required.