Please note, this modification requires soldering skill at board level and involves removing surface mount components. This modification will also void your warranty and all responsibility resides with the person making the modification. As the CTH comes fitted with a basic Bachmann decoder, the lighting functions are rather limited. This decoder only has two functions which means that the internal lights are always on and you either have red marker lights when the CTH is trailing or both the headlight and marker lights on when the CTH is leading. This install will allow full control of all four light circuits, namely the internal lights, the headlight and both red and white marker lights. CTH as supplied, while on powered track the internal lights are always on
The first step is to remove the body. The body is only secured by clips and is easy to remove by inserting something slim between the body sides and the under frame on both sides and the body should pop off. Removing the body CTH with body removed
With the body removed, you can then unplug the supplied Bachmann decoder. Body removed showing the top of the circuit board Remove the four black plastic clips that hold the power pickup wires from the bogies. These are labeled as VCC+ and VCC-. You can either set these aside to be reused later but the recommendation is to throw these and solder the wires. Next you need to unsolder the two wires that go to the switch in the under frame that enables or disables the headlights and marker lights. This is labeled as S3. Also unsolder the wires from the switch as this is no longer required. Once all wires have been disconnected, you can remove the three small black screws that hold the circuit board. It is easier and safer to fully remove the board but it can be left in if you are confident in doing so. Remove all five diodes, these are marked D4 through D8 and have the code M2 on them.
The TCS FL4 is a small 4 function, function only decoder. This means it can control up to 4 separate outputs that can be used for lighting or other low power devices but has no motor control which is perfect for this application. The reduced size also means it now fits in the roof cavity of the CTH above the circuit board, unlike the Bachmann decoder which sits in the luggage/guards compartment. Showing the size difference of the TCS FL4 (left) and the supplied Bachman decoder (right)
CTH circuit board with TCS FL4 wired in (ignore long blue wire) To install the FL4, you need to install a link bridging S3 where we removed the switch wires. Now solder the following wires to the following locations. RED (right rail) to the solder pad at the pointy side of D8 BLACK (left rail) to the solder pad at the pointy side of D7 BLUE (decoder common / V+) to the either solder pad between D4 and D5 GREEN (headlight) to a machine pin socket to form a socket VIOLET (white marker lights) to the solder pad at the non pointy end of D5 BROWN (red marker lights) to the solder pad at the non pointy end of D6 PINK (internal lights) to the solder pad at the non pointy end of D7 BLACK with WHITE stripe (decoder ground) leave unconnected. You can cut each wire to length for a cleaner install or leave the wires at their full length and just tape them in place. Screw the circuit board back onto the under frame and solder the four wires from the bogies back onto the VCC+ and VCC- locations. A further enhancement can be made by soldering the other end of these wires to the bogies directly, removing the reliance on those plastic caps. If you do this, you will have to file the blackening coat of the bogie tabs to allow the solder to tin them.
Close up of connection points FL4 and wires taped into place
Next is to modify the wiring in the body of the CTH. This involves removing the two screws that hold the circuit board in place and gently lifting the board loose and then unsoldering the magnet wire from the WHITE solder point next to the COM point. This wire is the negative wire to the LED headlight. On to the end of this wire solder a 1K resistor and a machine pin socket to form a plug and cover with heat shrink tubing. Reinstall the board with the wire poking out the back. modified body wiring for the headlight
Plug the headlight pin into the GREEN wire socket and clip the body back onto the under frame and place onto the track for programming. Ready to be put back together How you program your CTH is up to you so I will describe how I have set mine up as a guide only. Program the decoder address to match the address used in the CPH. this removes the need to run the CPH and CTH in consist mode. Function control; F0f not used. F0r Headlight on in reverse, this means the CTH is leading. F1 Headlight dim (known as Rule 17 in the US) This means on NCE ProCab and PowerCab systems, the BELL button is used to dim the headlights. In Australia, we have very few locomotives that have a bell remapping this function is fine. F3 Internal lights (this also means you have to remap functions on the CPH as the default is F11) F4 Marker lights, set up to be directional (also remapping in the CPH to disable the output)
When configuring the FL4, things to be aware of, is the instruction manual that is supplied has incorrect control CV s listed. Using JMRI/Decoder Pro to configure the FL4 does make the basic configuration easier but at this stage, the decoder profile doesn t list all the option. The main issue that is common to both the instructions and the JMRI profile is setting up Rule 17 and which function it responds to. JMRI/Decoder Pro screen for setting up the function mapping
JMRI/Decoder Pro screen for setting up lighting control After configuring the FL4 in JMRI/Decoder Pro you must then manually change CV 123 to set what function the dimmer (Rule 17) operates on. The value of 4 sets it to F1.