The intent of this document is to detail the process of installing a decoder in a Kato HO scale NW2 locomotive. A TCS M1 decoder is used as very little of the weight casting has to be removed due to the small size of this decoder.
The TCS M1 is a conventional (non-sound) decoder with two lighting functions supported by the Blue (12vdc source), White (F0F ‘Forward’) and Yellow (F0R ‘Reverse’) wires. The image to the right shows the size of the TCS M1 as compared to a Canadian five cent coin. The five cent coin is about 2.2cm in diameter.
The locomotive must be disassembled to install the decoder. This disassembly begins with the removal of the shell components. The cab must be removed first. This done by using a pointed tool to gently force the cab latch tabs away from the body shell and metal frame. The image to the right shows the location of the cab latch tabs, one on each side of the cab The image to the right shows the cab partially removed. The cab latch tab can be seen at the bottom edge of the cab. The cab will slide away from the frame and body shell without difficulty once the cab latch tabs are released.
Once the cab is removed the body shell is removed by lifting the cab end of the shell away from the frame weight. It may be necessary to use a blade to separate the shell from the shell latch on the frame casting. The image to the right shows the location of the shell latch on the cab end of the frame.
Once the shell is free from the frame casting at the cab end of the frame weight then the shell can be removed from the forward end of the frame weight. The image to the right shows the shell latch at the front of the frame weight. A slow, steady pressure moving the shell up and away from the frame weight will cause the shell and frame weight to separate.
Once the body shell has been removed the shell latch tabs are removed from the frame weight casting. This is done eliminate the need to pry and warp the shell should the shell have to be removed in the future. The image above shows the shell latch tabs removed with a Dremel abrasive disk. At this time an adjustable DC power supply is used to identify the polarity of the voltage application to cause forward movement. Set the variable DC power supply for approximately 5 volts. Touch the power supply leads to each half of the frame weight casting. Note the polarity required to cause ‘high end’ of the frame weight casting to lead the movement. The Dremel is used again to etch a ‘+’ (positive) symbol on the appropriate half of the frame weight casting.
The image above shows the frame weight casting separated revealing the enclosed motor. Be careful to not let the nylon nuts, worm gear tensioners and electrical isolation bushings get away from you. In the instance of this specific motor we now know that a positive voltage applied to the ‘white dot’ armature lead will cause the locomotive to go forward with the long hood end of the locomotive leading. Make a note of this detail for later use. Now is the time to confirm the stall current of the motor. The stall current is the current that the motor draws when the motor armature can not turn. The stall current is found by setting the power supply to 12vdc, connecting power to motor and noting the current when the armature rotation is prevented. The stall current must be less than 1 amp in order to use the TCS M1 decoder. The next step is to connect the decoder to the motor. When CV29 is set so as to have ‘Bit 0’ set to ‘0’ for ‘Forward direction normal’ the ‘Orange‘ wire of the decoder is positive with respect to the ‘Grey’ wire of the decoder. Therefore the ‘orange’ wire is connected to the ‘white dot’ connection of the motor which must be positive for forward movement of the locomotive.
A small amount of the frame weight casting must be removed (machined away) to make a space for the decoder. The image below shows the frame weight casting before the machining has been done. Note the marked area that has to be removed at the top, center of the frame weight casting.
The image above shows the frame weight casting after the required machining has been completed. Note the opening that has been created at the top, center of the frame weight casting. Note also the channels that have been created for decoder wiring. This simple machining has been done with a Dremel rotary power tool using ‘cut-off’ disks. Take the time to ensure that all sharp edges and burrs have been removed. Now is the time to gather all of the motor components prior to reassembly of the motor and frame weight casting. The image below shows the motor assembly and the parts that must be included. The bushings that fit on the end of the worm gears may have fallen off. Ensure that these bushings are in place. The couplers fit inside the cavity in the fly-wheel. These couplers may also have fallen out. Ensure that the couplers are in place.
The next step is to reassemble the motor and frame weight casting. The image below shows the areas where the motor armature originally made contact with the frame weight casting for power pick-up.
The image below shows vinyl tape that has been added to ensure that the motor armature can not make electrical contact with the frame weight casting. Note that the tape not only covers the original general contact area the tape also covers the frame weight casting cut-out area to sure no electrical contact with the decoder armature wiring.
The image below shows the motor and worm gear assembly placed in the left half of the frame weight casting. The motor assembly is placed on top of the vinyl insulation tape discussed on the previous page. Note that the electrical isolation bushings are in place. Note also the truck locator tabs. It requires a bit of dexterity to hold the trucks in place within these tabs while the two halves of the frame weight casting are placed together.
In the image below note the worm gear tensioning springs. These springs must be in place before the two halves of the frame weight casting are placed together. Note also that vinyl tape as shown on the previous page must be in place on this half of the frame weight casting also.
Care must be taken to ensure that the motor mount and the worm tensioning springs are all properly seated in their respective relief’s in the frame weight casting. The same holds true for the worm gear end bushings as well as the frame weight casting separator bushing. All of these parts must be properly seated in order for the two halves of the frame weight casting to fit together properly.
The next step is to prepare the long hood headlight assembly. The original long hood headlight assembly uses a ‘Yellow’ LED with a 270 ohm current limiting resistor and is designed to pickup power from the two halves of the frame weight casting. The original long hood LED headlight assembly is shown in the images below.
The original long hood LED headlight assembly must be modified to work with the decoder installation. The circuit traces on original long hood LED headlight assembly are removed so that the assembly has no connection with the frame weight casting. This is shown in the image to the right. The traces are gently abraded away with a Dremel cutting disk.
The replacement long hood LED headlight assembly is shown in the images below. The original ‘Yellow’ LED is replaced with a ‘Sunny White’ LED. The current limiting resistor now used for the decoder is 680ohms. The replacement long hood LED headlight assembly is also marked for polarity of the decoder wiring connections. The decoder ‘Blue’ wire is connected to the positive (+) point. The decoder ‘White’ wire is connected to the negative (-) point.
The next step is to prepare the decoder input power connections. The rail power is picked up by two spring clips that connect with the trucks and the frame weight casting. These clips are shown the image below. The clips are held in place by the fuel tank, to the right of the image below. Each half of the frame weight casting now has a wire relief channel. The spring clips must be notched on the inside so that the appropriate decoder wire (‘Red’ and/or ‘Black’) can pass between the clip and frame weight casting.
The appropriate decoder wire (‘Red’ and/or ‘Black’) is then solder to the underside of the spring clip as shown in the image above. After the power pickup clips are in place the long hood LED headlight assembly is installed with the appropriate wiring connection to the decoder. Ensure that the plastic coupler mounting clips are installed and orientated properly with the hole in the frame weight casting. Remember that the two halves of the frame weight casting must be kept electrically isolated. Should you choose to bolt a Kadee coupler to the locomotive you must use an Acetal (non-conductive) bolt to do so.At this point the project should resemble the image below. Now is the time to place the locomotive on a Service mode programming track and confirm that it is possible to Read/Write to various CV in the decoder. If the Read/Write process is successful it is reasonably safe to assume that the decoder is properly installed. Assuming that the locomotive successfully passed the Service mode programming Read/Write test place the locomotive on operational trackage and check the functionality of the locomotive with respect to motor control, free movement and long hood LDE headlight operation.
At this point the body shell can be placed on the frame. The ‘Yellow’ and ‘Blue’ wires are extended for eventual trimming and connection to the LED headlight in the cab. The next step is to prepare the cab LED headlight assembly. The original cab headlight assembly is shown in the image to the right. The original cab headlight uses a ‘Yellow’ LED with a 270 ohm current limiting resistor. The original cab headlight assembly has spring tabs that connect with the two halves of the frame weight casting for power.
The replacement cab headlight assembly uses a ‘Sunny White’ LED with a 680 ohm current limiting resistor. The appropriate ‘Blue’ and ‘Yellow’ wires are added for connection to the respective colored wires on the locomotive body. The cab is then re-assembled complete with all internal parts.
The cab headlight wiring is now attached to the appropriate color wiring extending from the locomotive. ‘Liquid Rubber’ is used to ensure that the soldered wire connections are protected against the possibility of an electrical short.
The locomotive is now ready for track testing and final programming to suit the end user application. The locomotive should be operated at various speeds in various directions for an hour or so to ensure that the installation is secure. After the locomotive has been track tested the operation proves satisfactory then the shell and frame should be bonded together. Remember that early in the exercise the frame to shell locking tabs were removed. The images below show the dabs of ‘Liquid Rubber’ that are applied to bond the shell to the frame. The ‘Liquid Rubber’ is used as it creates a firm bond rather than a permanent bond.
The ‘Liquid Rubber’ is applied in the area of the trucks where the frame has a flat contact with the shell.
Important Soldering Tip
Please do not use any flux either liquid or paste on the mother board. Over time, the acidic properties of liquid or paste flux will begin eating away at the fiberglass PCB and will damage it. Use only Rosin-core solder or no-clean flux approved for electronics use.
TCS recommends the use of Kester "44" Sn63 Pb37, .015" diameter Rosin-core solder. Kester part number 24-6337-0007.
You can order this solder from the following retailers:
Digikey - PN:KE1110-ND
Techni-Tool - PN:488SO6775
Other solder tips
When stripping wire, only strip a tiny little bit of the insulation. Strip no more then a 1/64 of an inch. When the wire gets tinned with solder, the insulation will shrink back more. Try to not expose any more wire then half the length of the solder pad at most. In no case should solder or exposed wire wire ever be outside the boundary of the the solder pad you are attaching a wire to.
Click here for important information on properly Stripping and Tinning wire