Building a Digitrax LocoNet tester

This is going to be another one of those posts where I wander a bit from the installation of DCC decoders but  this is good stuff to know if you use a Digitrax system and it ended up being a fun and easy project.

The little device in the photo on the left is called an LT1 and has 4 green 4 LED's that when lighted after being plugged into the Loconet indicate all is well.

Because the weak links are the flat telephone type cables and the rather delicate connectors it's important to have one of these on hand to verify that the connections are sound.

The LT1 comes with the system and they can also be purchased separately and they are not expensive.  The problem is that they are very small and easily lost.  They are also a goner if they get stepped on which can easily happen at a show if left on the floor.  I have had a couple of these and so has the Ntrak club I belong to but the last couple of show setups none could be found so I decided to try to make something that was a little bigger and not so easily lost.

I found this photo on wikipedia that shows the pin outs of the phone connector and what they represent on the LocoNet cable.

After a couple of experiments this is what I came up with.

I used a surface mount RJ11 phone jack that had 6 contacts.  These are about 2 inches square and about 1 inch thick.  Still small enough to easily fit in the toolbox but large enough not to get lost so easily.

The LED's are actually LED light boards from Atlas GP7 locomotives which in I had installed TCS CN-GP decoders in.  I re-mounted the LED's so they point straight up from the board.  I also used scraps of decoder wires to make the connections inside the box so this was really a junk box project.

Here is a look inside.  The back part and the cover of this phone jack just snap together.

The LED boards were modified by re-mounting the LED so that it is pointed straight out from the board.  Also I trimmed down the size of the boards so they would fit close together in the middle of the cover and stay clear of the screws on the back part.  The yellow and black wires are the commons so they each connect to two of the LED boards on the side that does not have the resistor. The other four wires are each connected to the side of the boards that does have the resistor.  Each of the wires are then placed under the screws.




Parts List:

• (4) LED boards from Older Atlas GP7's.  Similar boards would also work
• (1) RJ11 surface mount jack - widely available for about $1.00 each

The way to use this device is to get the command system going so that a train can run.  Then plug one end of a loconet cable into the command station and the other end into this tester.  All four LED's should light up, if they don't then there's a bad connection in the cable or at one of the connectors.  Re-installing a new connector often corrects the problem so a good quality RJ11 crimper and connectors should be kept in the tool box.

When setting up the DCC system on our Ntrak layouts, I have found the the telephone cords to often be unreliable so I will test each section of cord before actually using it to connect the command station to the various panels on the layout when setting up.  This method avoids much frustration.

Lenz Silver Mini in an Atlas Classic GP35

One of the Classic releases from Atlas were the GP35's that were closely based on the mechanism made for them by Kato several years earlier.  The Atlas Classic GP30 also uses the same mechanism as the one shown here.  At first glance this would seem like a straight forward replace the frame type of installation but as I discovered there are a few extra tricks that are worth covering.

If you look at the frames for the Kato made model and the Classic models made in China, they seem identical in every way.  They both even have the same part numbers on them and copyright Atlas 1992.

There is a critical difference and it's important not to get them mixed up.  The photo on the left shows the right side frames from each model.  The size of the bushings used on the Classic version are slightly smaller and where they fit in on the frame is also slightly smaller.




A quick way to check is to test fit a bushing from a Kato made model. If it fits easily then it's a frame for a Kato made model.  If it's a tight fit or won't fit then the frame is for the Classic version.

I was quite confused about this until John from Aztec set me straight.  The Aztec part number for the milled frame for a Kato made model is TM3001 and for the Classic model it is TM3016.

Because the outside of the Kato made and Classic frames seems identical, I wondered if the shells are interchangeable.  After swapping around several shells and frames I was able to confirm that yes, they are interchangeable.  So now on to the decoder installation.

This model normally comes with bright white LED's on a PC board very similar to the one used on the Kato made model.

On some of them there is a small component added to the solder side of the board.  This was added to suppress the flickering of the LED when the engine was running in the reverse direction in DC operation and will not be needed after the decoder is installed so it should be removed on both boards.

On the front LED board only there is a chance that the LED lead on the left side can short on the left side frame as shown in this photo.

The LED needs to be removed, a small tubing place on this lead of the LED, then the LED re-installed.  The Kato 77A LED board already has tubing on it's LED so I took some from those to use here.

I have also found some of these Atlas boards that have the circuit traces both sides (top and bottom) of the board. These have to have both sides cut to fully isolate that part of the board from the frame.

This photo shows the component side which normally does not have any circuit traces.






For the wire lengths I followed the Aztec instructions except that I added the blue wire and cut it to the same length as the yellow wire.

   Black & Red = 1-3/4",  White = 1-7/8",  Orange = 1"
   Yellow & Blue = 7/8",   Orange = 1",   Gray = 1-5/8"

This photo shows a summary of all the steps I did to get the decoder ready to install.  The wires on the Lenz decoder are soldered right at the edge of the decoder and I felt they might get broken during handling so the first thing I did was to gather them together in a heat shrink band.

This decoder had no heat shrink covering and it components were exposed.  This was the method I used to insulate it from the frame and from the rear LED board.

A scrap of .020 thick plastic was cut to fit on the frame, then the decoder was secured with some Kapton tape.  The Kapton tape is trimmed to fit around the bumps on the sides of the frame that hold the shell in position.

Here is a photo of the completed mechanism from the right side.  The gray decoder wire gets around the motor to the bottom brush using the slot milled in the right frame side.

Zimo MX621 in a Kato SD40 or SD45

This old Kato mechanism is one of my favorites and I think I've done more of these types of installations than any other.  The same mechanism is used for both the SD40 and SD45 models. The more recent releases take a board type decoder but for the older releases you will need to get the frame milled.  The Aztec Mfg. part number for a frame milled to take a small decoder is TM3002.

The decoder I am going to use in this one is the Zimo MX621.  It is similar in size to the TCS M1 and comes in a little plastic box.

Little boxes like this are perfect for storing spare motor brushes, brush springs, brush caps, etc.

The Aztec milled frame comes with clear instructions for the basic installation.  It is mentioned in the instructions about using the blue wire for decoders with transponders. This is because for the transponder function to work, the blue wire has to be connected as a return for one of the function wires.

As this decoder does have a blue wire, I am going to follow the option of using the blue wire as the return path for the yellow function wire on rear light board.

This photo shows the completed decoder assembly.

I have replaced the stock yellow LEDs on both boards with bright white LEDs.  On the rear board, I also replaced the stock 270 ohm resistor with a 750 ohm resistor.  This is because with the blue wire, the signal going to the LED is going to make the LED brighter and I wanted to reduce it to be close to the same brightness as the front LED.

The motor assembly goes back together in a very similar way as it does with most installations. What is different about this installation is that the decoder is in the fuel tank and all of the wires go up around the motor to the top of the frame.

This photo shows how everything is laid out just prior to re-installing the motor assembly in the frame.

This photo shows what it should look like on the other side of the right side of the frame after the motor assembly is placed into it.

The wires should lay side by side and not be twisted over each other.  It is also very important that none of them have gotten caught or pinched between the motor and the frame.

The rest of the reassembly of this model is very straight forward.  These are normally very quiet running engines but I have noticed ones that have sat around for years get a little noisy.  This is almost always cured with a small drop of Labelle 102 or other plastic compatible gear lube on the spots shown in this photo.



In conclusion, this would be a great model to try as your first wired decoder DCC install.  Other currently available decoders that would fit in the pocket milled in the frame would include the Train Control Systems M1, M4, or Z2, or the Digitrax DZ125 or DZ143.

Sending frames for milling

While the options for installing DCC decoders in N scale engines without the need to do major modifications to the frame are much better than in the past, there are still some cases where space will need to be created in the frame for a decoder, wires, resistors, etc.  For me the best option has always been to send my frames to Aztec Manufacturing in Carson City, Nevada.

This is a professional machine shop specializing in model railroad products and they do a much better job than I could ever do.  They only charge $10.00 for most N scale frame milling, and for me it's always been money well spent.  They have a list of frame milling available and prices at  http://www.aztectrains.com/dccframes.html.

If you send several frames at one time you can reduce the cost of shipping per frame.  I like to use the Priority Mail small flat rate box for the best savings.

You'll need to first completely disassemble you engine so that just the frame gets sent in.  Be sure to account for all the small parts including nuts and shoulder washers as those sometimes get stuck to the frame.  I use small plastic zip lock bags that I purchased on ebay to store all the small parts.  I put the motor in a separate small bag so that no small parts can get into it.  I normally put the shell, trucks, and fuel tank in the original box.  If there is more than one engine being disassembled at the same time I will mark all of the bags so the parts don't get mixed up.




This photo shows how I bag up and label the engine parts until I get the milled frame back from Aztec.  If you have several of the same model that you are working with at the same time, label the bags by road number or just 1, 2, 3, etc.





To contact Aztec Manufacturing:

Aztec Manufacturing Co.
2701 Conestoga Drive, # 113
Carson City, NV 89706

775-883-3327

TCS Z2 in an Atlas SD35

As I model the Southern Pacific, many of my engines have the nose lights modeled but not lighted.  It's easy to add this type of lighting when installing a decoder using one of the pre-wired surface mount LEDs.





As this installation is otherwise very similar to several others I have presented, I will skip over some of the common points and focus more on what is unique to this installation. See my posts on the Atlas SD50 and GP40 for details of the basic decoder installation.

Once the shell is off a quick check of the mechanism indicates that there is room for a small wired decoder like the TCS Z2.

The original Atlas LED board is used after all of the modifications shown in this photo are done.  Note that an additional hole is made in the front part of the board for the nose LED wires.

This is also the time to replace the stock LED's with bright white LED's if desired.

While no modifications to the frame are needed for a standard installation, I did make grooves on the front of the left.frame for the LED and it's wires.

This photo shows what I had to do to the frame and the type of LED I used.

Here is a look at how the nose light LED is installed and connected to the LED on the board.  The ends of the wires will need about 1/8 inch of the insulating enamel scraped off before they can be soldered on the board.


Using a Z2 decoder and wiring this extra LED in parallel will mean that the nose LED will turn ON and OFF with the F0 function.

TCS Z2 in a Bachmann Spectrum 44 tonner

It's been a couple of months since I've posted anything but I have been kept busy with installs.  They've mostly been routine ones that I had already covered on this blog.   But recently I was asked to replace the decoder in a Bachmann Spectrum 44 ton switcher with a TCS Z2 or similar small decoder.

I was not very familiar with this model so I checked it out on the web.  It seems that Bachmann offered this model only in a DCC version and that no DCC manufacturer offers a replacement decoder.  Also on some of the forums there was mention of problems with programming this decoder.

This model uses the tested method of bumps on the frame / dimples on the inside of the shell to hold the shell in place.  It's a tight fit and after trying a few methods to get the shell off,  this was the one I found the easiest.

The trucks will come off fairly easy so I took them off first then placed a jewelers screwdriver between the fuel tank and the shell and gently pried.

Once the shell is off, we can see the original decoder board.  The decoder is secured to the frame with 2 small screws, one on each frame half.

The decoder has mostly surface mount components with a couple of coils on the bottom and what the instruction sheet called a thermal fuse link in series with the motor.

The way this component was installed in the motor wiring instead of on the board suggest to me that it may have been an after thought.

I made two custom LED boards from a two stock Kato LED boards that I had in my collection.  This photo shows the modifications I made to get what I wanted.

Here are the 2 new LED boards that I made from a Kato LED boards.  Don't know what engine it originally came from.  I wanted something with surface mounted LED's.  The new boards are secured to the frame by the original screws and provide track connection to the decoder.  I spliced the decoder wires onto the motor wires so I would not have to remove the motor.

Here's the side view of the finished mechanism.  One of the nice things about the LED boards I made was that they are single sided meaning that I don't have to worry about anything on the bottom shorting on the frame.  The space where the coils of the old decoder were could be used to add a bit of weight.

The inside of the shell of this loco offers an opportunity to add quite a bit of weight to this loco in the cab where the black plastic box that was attached to the original decoder had been.   I painted the inside of the cab windows a dark gray, then attached 2 layers of lead strip to the roof.   Another area where weight can be added is along the inside of the cab side walls below the side windows.

If the replacement LED boards, decoder, and wires are not interfering with the shells fit, the shell should rest on the parts of the frame that stick out as shown in this photo.

Here is the completed engine.  With the weight that was added it is close to the same weight as a stock Life Like SW type switcher and has about the same pulling power.

TCS CN-GP in an Atlas SD9

The Atlas SD7 and SD9 releases from the early 1990's that were made by Kato work very well with the TCS CN-GP decoder.  This example uses an SD9 but the mechanism is identical for the SD7.  First step is to completely disassemble the locomotive.

Only a few minor modifications are needed on the frame at the locations indicated in this photo.  I use a Dermal rotary tool with a cutoff wheel to do this and then I smooth things out with a jewelers file.



In this photo the modifications have been completed.   Be sure that the frame sides are free of any loose bits of metal before re-assembly.  An old paint brush works well for this.








After removing the brushes from the motor, file a groove from top to bottom of the motor as shown in this photo.  It should be large enough for 1 of the decoder wires to fit in it.  It's important that this wire does not get pinched between the motor and frame after the engine is re-assembled.





To test that the wire has clearance, thread a scrap of decoder wire through the motor saddle, around the motor and groove as shown with the motor and motor saddle temporally re-installed in the left side frame.  The wire should move freely.





Next remove the orange & gray motor wires from the front decoder board and solder them to the brush caps.  Re-install the brushes without the contact tabs.


Secure the wire from the bottom of the motor in the groove with adhesive of your choice.  I've used Walthers to do this but lately I've been using E6000 which I purchased at Tap Plastics.




Install the motor assembly, and worm gears into the left side frame as shown here.  The motor wires should come out of the notch on the top of the frame and not be pinched in any way.



Reassemble the frame sides and install the trucks, contact strips, and fuel tank.  Leaving the motor wires long, solder them temporarily to the points shown here to test run the engine.  If it runs backwards then reverse the motor wires at the decoder.












Here is the completed installation less the engine shell.  The wires must lay flat on the top of the frame for the shell to sit correctly.  There is a bit of room for extra weight if desired.

TCS Z2 in a Micro Trains FT

Anyone who has followed this blog will notice that I am a fan of TCS decoders and use a lot of their Z2 model.  I have found it to be a great decoder, small enough for many applications and robust enough for any N scale engine.  TCS does not make a board type decoder for the Micro Trains FT so I wanted to see if I could wire in a Z2 and found it to be a relatively easy install.

The first step is to remove the shell from the frame.  On the front of the A unit, remove the screw then pull the coupler out forward.

On the rear of the A unit and both ends of the B unit, removed the coupler and mounting frame together.

After removing the shell, the LED light board is exposed.  Just behind the board there is an indent in the frame that is large enough for a wired decoder.  Remove the black light shield and then the board. That's right, the frame won't have to be taken apart on this one.



The boards in the A units will have the LED along with a couple of other components.  Remove the two that are pointed out in this photo.  They were needed for the DC operation of the bright white LED but will not be needed for the decoder function output. 

The board from a B unit will not have any components on it at all so this step can be skipped.










I have found the quickest way to isolate all the parts of the board is to cut a notch on each side of the board through the two circuit traces.

This step needs to be done on the boards for both the A and B units.








Here are the lengths I cut the wires to. 

Blue, white, gray, yellow = 1"
Orange = 1-3/8"
Red, black = 1-5/8"








Kapton tape is best to use for insulating the frame but does not stick to the frame as well as Scotch tape.  I clean any oil off the frame of course, but then I use a layer of Scotch tape first then apply the Kapton tape.  It sticks very well to the first layer.

Connect all of the decoder wires as shown in this photo.  This can be done either before or after the board is re-installed in the engine.  The photo shows an A unit.  The B unit won't need the white and blue wires.

Special note on the B units

FT's were run with the B units oriented backwards in relation to their associated A unit and were often draw bared together.  This is noticeable by the two sets of ladders, the offset of the wheels and fuel tank, and the dynamic brake vents on the roofs of the ones that had dynamic brakes.  The PC board in the Micro Trains FT B unit is oriented in the opposite direction as the A unit.  This would have not mattered running DC but with DCC we must have a front and a back end to each locomotive.

Here is a prototype photo showing an A B set arranged this way.

This photo showing an A B set with the shells next to a pair of mechanisms shows what is going on.  This can be corrected by programming the B unit for reverse operation

CV 29 = 07 for 2 digit address
CV 29 = 27 for 4 digit address

TCS CN-GP in an Atlas GP7

Between 1995 and 1997 Atlas did several releases of N Scale GP7's and GP9's based upon this mechanism.  The TCS CN-GP decoder is a perfect choice for these. 

The frame requires some very minor modifications that I do using a Dermal rotary tool with cutoff wheel.  The small ridges between the light board clips at each end will need to be removed and also a notch needs to be made on the left side frame at the point shown in this photo.

On some GP9 releases the frames have interlocking tabs.  If you have one of these just snap off the upper tab.  This will create the space needed for the motor wires.






In this photo all of the frame modifications are done.  Also shown is the plastic motor saddle with a  notch on the top.  The notches on the frame and the saddle are needed for the motor wires.

Remove the brush caps from the motor and remove or cut the contact tabs.  Then remove the orange and gray wires from the decoder and solder them to the brush caps.  File a slot big enough for 1 wire on the left side of the motor.  With the orange wire going to the bottom, re-install the brush caps with wires and motor saddle.

Re-assemble the locomotive mechanism with the orange and gray wires going through the hole on the top of the left side frame and the plastic motor saddle.

Install the CN-GP decoder boards on the frame and connect the yellow, black, and blue wires as directed in the decoder instruction sheet.
Cut the orange and gray wires to the correct length and re-solder to the front board.  All wires should lay flat and not overlap on the top of the frame.

Re-install the trucks, contact strips, and fuel tank.

These Atlas GP7's were among the first N scale engines to have lighted number boards with the numbers already in them.  Because the LED they used was so dim, this feature was not really noticeable.


With the bright white LED's that come with the CN-GP decoder, this feature can now be fully appreciated as seen in the photo above.  You may even find it necessary to mask for paint the inside of the shell at the ends if the light shines through the shell.