Digital Command Control

Installing DCC Decoders in N Scale Locomotives

Just as Plug & Play doesn't always work as advertised on computers, sometimes some extra effort is required to make Plug & Play (PnP) decoder installations work just as they should in N-scale locomotives. The following are some general problems encountered and suggested solutions.

General There is usually more than one decoder from more than one manufacturer that will fit or work in your particular locomotive; check each out then select the one with the desired features, best price, best reputation, etc. For some locomotives, even though the decoder is essentially "drop-in" you may have to do some soldering, such as the wires to the headlight.

Kato E8/9 A/B, F3/7 A/B, F40PH, P42, PA/PB-1 To remove the original light board and install the decoder, you must remove the plastic clip holding the motor brush leads against the light board and bend the leads up. After the decoder is installed you are directed to bend the leads back down against the decoder contact pads and secure them with the plastic clip.

The problem is that in bending the motor brush leads up so you can remove the original light board and insert the decoder, you cannot bend them back to the exact same tension. Thus when the retainer clip is inserted the motor brush leads may or may not be making a good contact with the decoder motor pads. Even if they are when first installed, simply replacing the shell on the frame or the vibration of running the locomotive may cause the contact to go bad.

The solution is to spot solder the motor brush lead to the decoder motor pad, using a very small amount of solder. (You may sometime in the future need to disassemble the locomotive for maintenance.) Be sure the soldering iron is 15 watts maximum and has a small round tip. Be sure to use resin core solder only.

All Atlas Diesel Locomotives that Utilize a Drop-In Decoder Atlas diesel locomotives that feature a drop-in decoder installation have a potential issue with the motor brush leads making good contact with the motor pads on the bottom of the decoder; the motor brush leads can move. This may result in no or intermittent operation. Repeated attempts to align the motor brush leads may or may not be successful.

The best solution is to solder wires between the decoder motor pads and the motor brush leads. Use a very small gauge stranded wire for this purpose (such as the wire used in Digitrax wired decoders). About ¾" long is enough. Strip 1/16" insulation from the ends of each wire. Cut the motor brush leads back about ¼" so they cannot interfere with the solder connection to the decoder motor pads. Solder one wire to the left motor brush lead, then to the left decoder motor pad. Repeat for the right side. Be sure there are no solder bridges between the two decoder motor pads.

You must be sure that neither the installed wires nor the copper brush leads can touch the metal frame or you will destroy the decoder. Use small pieces of Kapton tape to prevent shorts.

Thickness of Plug & Play Decoder Circuit Boards The circuit board of the Plug & Play decoder that you select for your locomotive may not be exactly the same thickness as the light board it is replacing. This may result in poor electrical contact with the frame, particularly if the decoder board is slightly thinner than the light board.

If the decoder board is slightly thicker than the light board use some extra but gentle force to place the decoder in the correct position in the locomotive frame. Don't use too much force as the circuit board is easily damaged.

If the decoder board is slightly thinner than the light board and does not fit snugly then you will need to build a very small solder dome on the power contact points at the four corners of the decoder. Do this very carefully, as you want to end up with a snug fit, but remember that the decoder must slip into the slots in the frame. Use a soldering iron with a small round tip and 15 watts maximum. Heat the decoder power pad with the soldering iron while applying solder until a very thin dome forms, then remove the soldering iron and allow to cool. Very carefully insert (do not overly force) the decoder in the Atlas frame and re-assemble the locomotive. If a great deal of force is required then the solder dome is too high; remove some solder with the soldering iron and try again.

Older locomotives generally must use a wired decoder to convert the locomotive to DCC. This may require the purchase of a retroframe or milling of the OEM frame, or you may modify the frame yourself. Information about retroframes and modifying frames, as well as the tools you will need to perform your conversion are listed below.

Even if your locomotive is DCC-ready you can generally install a wired decoder, probably without modifying the frame. Several of the descriptions below give directions on installing wired decoders in such locomotives.

Retroframes

Locomotive frames must be precisely manufactured to give the correct orientation and tolerances for drive train components, and alignment of the motor and electrical pickups, etc. to produce a smooth-running and quiet locomotive. Aztec and Southern Digital follow different approaches in the way they produce their retroframes.

Aztec uses OEM frames from the locomotive manufacturer or the customer and mills them on precise computer-controlled milling machines to create wiring channels and space for the decoder. These frames do not void the manufacturer's warranty, and most manufacturers will accept locomotives with Aztec frames for repair.

Southern Digital creates a copy of the die cast original frame modified with the wiring channels and space for the decoder. These are then copy cast in rubber molds in lower temperature, but more dense, alloys than the original.

Each approach achieves its purpose of converting an analog locomotive into a digital locomotive. The following table indicates some of the differences between the approaches and the companies:

Currently, frames are, or have been, available for the following diesel locomotives:

Notes:
Due to short supply of some OEM frames, Aztec may require your existing frame as a trade-in. Check at their web site: http://www.aztectrains.com. Aztec also posts the instructions sheets for installing decoders in the frames they produce. Check their web site.

Southern Digital Digi-Frames are fairly brittle, and have been known to break from incorrect handling or dropping of either the frame alone or the frame in a locomotive. Southern Digital also had, at one time, some problems with frame dimensions; watch out for these if purchasing on the used market or over the Internet.

New frames are added by the manufacturers from time to time, and some are discontinued, so check with the manufacturer or dealer for availability.
 

Suppliers Addresses: The manufacturers of retroframes for N Scale diesel locomotives can be contacted as follows:

Modifying the Frame Yourself

You can also modify your own existing frame to accept a DCC decoder. If you have the tools, time and inclination, you can avoid purchasing another frame.

Be extremely careful when modifying/grinding Kato or Atlas/Kato frames that you do not damage or destroy them. Most are no longer available from Kato or Atlas.

Details are provided in the individual publications for locomotives where this is an option.

Tools Required

If you are going to use a commercially available retroframe and/or modify your existing frame you will need the following tools:

How to Use Installation Descriptions

Keep the following in mind when choosing a description to follow:

• The various conversions listed below provide detailed descriptions covering installations actually performed by model railroaders throughout the world, and reflect the experiences encountered during those installations.

• After selecting the locomotive manufacturer below, from the listing click on the author's name(s) corresponding to the desired locomotive to go to the detailed installation description.

• Many locomotives have been released several times over the years, many with updated tooling and frames. Thus each description for a specific manufacturer and locomotive model may not apply to your specific locomotive. Carefully compare your locomotive to the locomotive pictured in the descriptions.

• Many of the descriptions refer to descriptions on the Train Control Systems (TCS) web site. All of these descriptions use TCS decoders. You should be aware that equivalent decoders may be available from one or more other manufacturers.

• Note that some descriptions are located in the files area of various Yahoogroups DCC-related lists, and may require membership in the list for access. Also note that articles published in the model railroad press are not generally available online. Contact the publisher to order a desired issue.

• No claim is made that this list is complete. If you have a locomotive that is not listed here you should use Google or Bing to search for a description for your specific locomotive. New descriptions are being published all the time.

Index by Manufacturer

• Instruction sheets for various locomotive conversions from Aztec Manufacturing Company, N Scale of Nevada, Southern Digital, Train Control Systems and others.

• "N Scale Digital Decoder Installation," by Paul Lator, Clinic Presented at NMRA National Convention, Atlanta, GA, July 20, 1995. (Paul Lator is owner of Southern Digital).

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Last updated: Monday January 22, 2012

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