Converting a SCX Compact Slot Car to Carrera Digital 143

By Michael Ashton

SCX Compact 1/43rd scale slot cars are among the best ready-to-run cars available in this scale. And although SCX has not released any new 1/43rd scale cars recently, they are still available in a few stores and on the Internet, if you are willing to search both diligently and persistently. I happen to have several SCX Compact NASCAR COTs that run quite well on the Carrera GO!!! track, so I would really like to add them to my growing stable of D143 cars. In order to do this they must be converted to the D143 system by installing the Carrera D143 decoder chip. This article is a brief step-by-step account of how this can be done.

Preparation

Look here to see a list of the minimum tools required for this type of conversion, tips on preparation and some cautionary advice that may help avoid mistakes. I rate this conversion as somewhere between low and moderate difficulty. Basic soldering and minimum modeling skills are recommended.

The Steps

After selecting a SCX Compact car to convert, and obtaining a Carrera D143 decoder chip/motor assembly, the first thing to do is compare a typical D143 and SCX Compact chassis side-by-side. This will allow planning to determine exactly where to create the opening for the D143 emitter and mounting post for the D143 circuit board.

The following photo shows a typical Carrera D143 chassis on the left and the SCX Compact chassis to be converted on the right. The D143 chassis does not have a decoder chip installed because the motor/chip assembly was removed and will be used in the SCX Compact conversion. There are three primary steps that must be accomplished for a successful, reliable conversion of the SCX chassis to D143:

1. An opening must be created in the chassis floor, in the correct location, that allows the emitter on the decoder chip to communicate with the sensor on the D143 lane change and lap counter track sections.
2. The decoder chip must be connected electrically to the pickup guide and motor terminals.
3. The decoder chip must be secured to the chassis floor so that no movement is possible.

Again, looking at the photo below, the yellow arrow points to the D143 chip mounting post which accepts a screw that holds the chip tightly in place. The red arrow shows the chamber which forms the opening through which the emitter communicates with the track sensor(s). In my opinion, the most secure chip installation and accurate digital performance will be achieved by duplicating these two structures in the SCX Compact chassis. So that is exactly what is going to be done here.

The Process

The first step in creating the opening for the D143 chip emitter is to determine the optimum location on the SCX chassis. The two important coordinates are: 

1. The distance from the center line of the chassis to the center of the opening. Ideally, we want the emitter to travel directly over the track sensor.
2. The distance from the leading edge of the guide flag (guide pin in the case of Carrera) to the center of the opening. The correct distance here ensures that the lane change flipper will activate prior to the arrival of the leading edge of the guide flag. Too long a distance could cause missed changes or even collisions with the lane change flipper.

In actual practice I have found these measurements to be not so critical. Just try to locate the opening as close to the position in the Carrera chassis as possible while still allowing for a secure chip installation and connection. The following two photos should provide a good depiction of where I drilled the hole in the SCX Compact chassis. Note that the leads that connected the motor to the copper strips leading to the guide pickups have been clipped.

To create the chamber for the emitter opening I used a short piece of 3/16” styrene tubing. The height of the chamber should be gauged to enable the D143 chip to sit level (i.e., no tilt) when the emitter is fully seated inside the chamber. Cut the chamber one or two mm higher than needed so that it can be adjusted by sanding the top after being glued in position.

The notch shown in the previous photo is needed because the opening in the chassis floor abuts the reinforcing rib that runs along the outer edges of the chassis. This allows the chamber to be centered on the opening without cutting the reinforcing rib and possibly compromising the structural integrity of the chassis. The chamber is glued in position using two-part plastic epoxy, mainly for that glue’s superior strength. See the photo below.

Below we see the finished chamber, sanded to the proper height and painted to match the chassis.

The mounting post is fashioned with a similar method. I used a short piece of 1/8” styrene tubing. Fist cut the tubing to the approximate height. Then use the D143 chip’s mounting screw to “self tap” into the post. Then remove and reinsert the screw several times until it is relatively easy to remove. Mount the loose post to the D143 chip through the chip’s mounting hole. Now you can test fit the position and height of the mounting post by seating the chip’s emitter into its chamber. Sand the end of the post, if necessary, to achieve the level orientation previously mentioned. Next, with the post still screwed to the chip, apply glue to the end of the post and place the post/chip assembly into position on the chassis floor with the emitter fully seated in the chamber. Apply pressure until the glue has set and then allow the glue to fully cure. Finally, gently remove the mounting screw and finish the post by applying epoxy all around the base. Painting to match the chassis is a finishing touch. The finished mounting post and emitter chamber are shown in the photo below.

Now that the D143 chip mounting structures have been created, it is a fairly straight forward process to install and connect the chip/motor assembly into the SCX Compact chassis.

Shown in the following photo is a typical D143 decoder chip/motor assembly. When converting a car to D143 my preference is always to use an existing D143 decoder chip/motor assembly when possible. The SCX Compact motor will work, but the D143 motor is known to be a good match for the decoder chip.

However, one characteristic of this assembly that presents a problem for installing in the longer SCX Compact chassis is how short the connecting leads are and, therefore, how close to the motor the chip resides. In the standard Carrera assembly, the positive output connection lead from the chip and one lead from the RF noise reduction capacitor are connected to the motor can as highlighted by the red arrow above. A common lead from the motor can, in turn, connects to the positive motor terminal. So all three wires are effectively connected to the positive motor terminal via the motor can.

Moving the chip’s positive output lead and the capacitor lead connections directly to the positive motor terminal, as shown in the following photo, allows the chip to be moved almost 1/2” farther away from the motor. This provides the additional flexibility in positioning required by the SCX Compact chassis.

Normally at this point the D143 chip’s input leads would be soldered to the copper guide pickup strips to complete the electrical connections. However, in this particular conversion I decided to install a quick connect micro plug assembly which allows the chip/motor assembly to be easily installed and removed. This allows the chip/motor assembly to be moved among different cars that have the plug assembly installed. This is a relatively simple process where the female (jack) is soldered to the chip’s input leads and the male (plug) is soldered to the copper pickup strips, as shown by the yellow arrows in the previous photo. If you don’t want to install the plug assembly, just solder the chip input leads directly to the copper guide strips.

The following photo shows the final assembly with the motor snapped into position and the D143 chip secured by the mounting screw with the emitter seated in the chamber.

This side view shows the emitter fully seated in its chamber (yellow arrow) and the chip sitting relatively level, secured by the mounting screw.

A view of the underside of the chassis shows the orientation of the emitter in the chamber.

One final recommendation: the SCX Compact cars perform very well on the Carrera GO!!!/D143 track. However, if your layout contains banked curves (as mine does), it will probably be necessary to eliminate the sharp square profile of the guide flag’s leading edge, as it tends to catch on the bottom of the slot on these track sections. The red arrow in the following photo highlights the SCX guide leading edge after being “nipped” and smoothed over with some light sanding.

So, it required a little effort, but I’m convinced that the final result was worth it. The SCX Compact cars in general look good, are quite true to scale and handle very nicely. If you are able to acquire, or already have one or more of these cars, and think that you would like to run them on a Carrera D143 track—go ahead. You won’t be disappointed.

A video of the SCX Compact Toyota COT converted in this article, running on a Carrera D143 track can be seen here.

_Michael Ashton