Tag Archives: decoder

Atlas MP15DC Decoder Install

Atlas MP15DC Decoder Install
I recently purchased this used Atlas MP15DC, and of course it needed a decoder. Since I’ve been more or less standardizing on Digitrax for my “run of the mill” decoders, I chose the Digitrax DN163A3, which is a “drop-in” version for this locomotive. TCS also makes a drop-in decoder, and of course a wired decoder can be used.

At low speed, this is one of the smoothest running locomotives in my fleet, even with the factory-default motor settings. There is an audible whine at higher speeds, but… this is a switcher. It’s not supposed to run at high speeds.

The install is so straightforward (and so typical of modern Atlas locos) that I won’t go into much detail here.

  1. Remove the shell
  2. Loosen the two frame shell screws
  3. Slide the light board out of the frame
  4. Place the decoder in the frame, with the large, wide end facing away from the cab end of the loco. Make sure to place it component side down, or LEDs up.
  5. Tighten the frame shell screws
  6. Replace the shell

The most important part of the install is to make sure the components face down when placing the decoder in the frame. The fit between the decoder tabs and the frame slots was quite tight, and required some force to get the frame to close up. If yours is loose, adding a little bubble of solder to the pads can take up the free space.

I also read in another install description that sometimes the motor tabs need to be trimmed or filed down just a bit to avoid incidental contact to the wrong tabs. I did not find this to be necessary on my loco, but be advised.

There was one thing that caught me off guard that I have not seen documented elsewhere, at least not with descriptive photos. There is a black piece of plastic inside the cab area of the shell that acts as part of a light guide for the rear headlamp. This piece is only press-fit, and seems to be able to fall out easily. Since I wasn’t expecting the part to fall out, I did not see where it fit originally, and it took some time to figure out where it went and how it fit into the loco.

To save you the trouble, here are a couple of photos:

The part is circled here.
Atlas MP15DC Decoder Install

This is where it goes… oriented upright like a chair, with the clear light guide poking through the hole in the black part.
Atlas MP15DC Decoder Install

One more tip… it’s easier to keep this light guide part in place if you flip the shell upside down and insert the frame into the shell, rather than placing the frame upright and putting the shell over it.


Con-Cor / Rivarossi N Scale 4-6-2 “Pacific” Decoder Install (Part 2)

In Part 2 of this install, we’ll explore the trickiest problem involved in this install:  connecting power from the tender to the locomotive.


Older versions of the Rivarossi 4-6-2 used a plastic drawbar, and only the little spring wire pressing against the drawbar pin in the locomotive to transfer power.  For a DC locomotive, this turned out to be a fairly poor design, but for a DCC install, it makes isolating the tender from the motor pickups easy.

(Un)fortunately, this version of the model uses a metal drawbar, which is much better for ensuring good power transfer under DC, but makes it much trickier to isolate the tender from the motor.

A few options that either I considered or were suggested, which I rejected (and the reasons why):

  • Enlarge the hole in the loco end of the drawbar and put shrink wrap over the drawbar pin.  I was concerned about friction and wear on the shrink wrap, so no.
  • Replace the drawbar with a plastic one.  This would have been an excellent option if I could have disassembled the pin at the tender end.  I couldn’t figure out how without destroying it.
  • Insulate the axle wipers from the bar rivets and wire directly to them.  Again, I was concerned about wear, and I just didn’t have the parts.

In the end, the simplest solution seemed to be to cut the brass bar.  It would have been much easier if I could have removed it from the tender first, but it’s riveted in place, so no.  Instead, I used a drill press to drill up from the bottom where there’s an opening in the plastic, and then cut the rest of the way through the bar with a Dremel tool and a reamer bit.  I did a somewhat messy job of it, but it worked.

Here’s a view of the bottom of the tender before the cut. You can see the opening where I made the cut on the left.

Once the cutting was done, I soldered a piece of wire to the bar in the middle of the tender and routed it through the hole to the front near the drawbar. At the drawbar end of the wire, I attached one pin of a NEM651 female connector and shrink-wrapped the connection.


Finally, I finished the end of the wire coming from the loco with a single pin of a NEM651 male connector. At that point, we’re done except for buttoning things up and testing her out.


I found when testing that with the female socket secured to the tender, it was very difficult to connect up the locomotive on the track. The quarters are very tight between the cab and tender, and I had cut the loco wire just a tad short. By leaving the plug loose, I was able to bring it out of the tender enough that the wires can be connected before the drawbar is hooked up. Much easier, and with everything being black it still looks OK. We’ll see what the customer thinks. I hope he likes it.


Con-Cor / Rivarossi N scale 4-6-2 “Pacific” Decoder Install (Part I)

I was recently asked by a friend to install a decoder in an N scale Con-Cor / Rivarossi 4-6-2 “Pacific” locomotive. It seems that install instructions for this model are scarce, so I will share how I managed.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2
(shown with the steam-dome shell screw partially removed)

This locomotive model has an odd (really, just old) method of pickup. The fireman’s side (left, going forward) rail is picked up through the drivers, while the engineer’s side (right, going forward) is picked up through the tender. Power is transferred from the tender to the engine through the drawbar and a stiff bit of spring-wire that contacts a peg sticking down below the cab.

This is actually the trickiest part of the install. The drawbar peg on the engine is directly connected to the lower motor brush, and the drawbar itself is conductive. So in order to isolate the motor from the rails, you have to somehow insulate the drawbar and provide an alternate path for the tender pickup to the decoder. More on that later.

For this install we chose the Digitrax DZ126T as the best balance between cost and size. The TCS Z2 (also a good choice) is slightly smaller but more expensive. The Lenz LE077XF is only a little more expensive than the Digitrax, but is the largest of the three. Any of these would work, though, and would follow the same basic install process.

The first step is to locate a good spot to fit the decoder, and do any necessary milling or other modifications to make room. Another install page showed installing the Lenz decoder under the cab roof, after some milling to the inside of the roof and to the top of the frame. On looking at the frame design, I decided to fit the decoder into the boiler where the upper headlamp contact is. There is room for the DZ126T at that location without any frame modifications.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

Remove the shell by taking out the screw in the top of the steam dome on the boiler and then spreading the firebox sides slightly. It is a tight fit, but with some shaking the frame will drop out. Next, remove the two headlamp contacts from the center of the frame and disconnect the black wire running from the upper contact to the rear of the locomotive. Keep the lower contact. You will need it later. Also remove and keep the spade lug on the back end of the black wire. The upper contact and the wire itself can be discarded.

Next, I test-fit a pre-wired T1 white LED that I had handy. It fits nicely into the brass slug that previously held the headlamp. I went ahead and used this pre-wired model, but next time I would probably custom build a T1 LED and resistor to make it as compact as possible and make a little bit more room for the decoder. The shrink wrap on this LED assembly got in the way.
DCC decoder install in a Con-Cor/Rivarossi 4-6-2
Pre-wired T1 LED in the boiler

DCC decoder install in a Con-Cor/Rivarossi 4-6-2
Test fit of the pre-wired LED

After test fitting, I trimmed the LED assembly as short as I could and wired it to the decoder. The decoder Blue wire (common +) goes to the current limit resistor (connected to the LED’s anode) (red wire) and the white wire (forward headlight function) goes to the cathode.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

The upper brush contact of the motor contacts the frame through a brass spade lug. We must remove that lug, turn it around to face away from the frame, and attach the decoder grey wire to it.

To remove the motor, you must first remove the lower brush contact. Pull straight down on the white plastic ring around the tender pin until it comes loose. Be very careful. It is a tight fit, and when it comes loose it is likely to fly off, taking the spring and motor brush with it.

Next, pull the motor out of the frame by pulling (or pushing) straight back firmly but gently. Remove the spade lug tab from the top motor contact and solder it to the grey decoder wire. Solder the spade lug removed from the lighting tab wire to the orange decoder wire.

After measuring for proper length of the grey and orange wires (they’ll reach back from the decoder position over the top of the frame), I cut and soldered the wires to the spade lugs away from the loco to prevent overheating the motor brushes.

Aesthetically, it would be better to solder the grey wire to the bottom contact and the orange wire to the top contact, so the orange wire is hidden from view. This would make the motor run in reverse, but that can be corrected by programming the decoder.

I lined the inside of the back of the motor mount hole in the frame with Kapton tape to ensure no contact between the brushes and the frame. This might have been overkill but I wanted to be extra-safe.

Reinstall the motor in the frame and reinstall the lower brush contact and tender pin. Slip the spade lugs back onto the motor brush contacts with the tab pointing back away from the frame.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

Once the motor is back in place, bend both spade lugs flush with the back of the motor.

Now, we’re almost done.

Cut and solder the red decoder wire to the lower headlamp tab and re-insert the tab into the frame. Secure the decoder to the top of the frame where the upper headlamp tab used to be. Tuck and secure all of the wires. The black wire should run back along the Engineer’s side of the frame where the black headlamp wire used to be, and will stick out the back of the cab for some length. The yellow wire can be cut short and tucked.

DCC decoder install in a Con-Cor/Rivarossi 4-6-2

Bend the red wire tab up a little past vertical. This will ensure the red wire is not sticking down where it can be seen when the shell is re-installed.

Slip the headlamp into the hole in the boiler slug, then carefully reinstall the shell. It is a tight fit, so you may have to do some “encouraging” to get everything in. It helps to take a small screwdriver and tuck the black wire under the lower edge of the boiler to hide it, much the way one would tuck a cable beneath the baseboard of a house wall. Be careful not to damage anything.

At this point, you should have a complete, running locomotive, except the black wire is sticking a few inches out the back of the cab. To test the locomotive, use an alligator-clip test lead to connect the black wire to the engineer’s side rail of your test track. The locomotive should power up, respond to DCC commands, and run (at least as far as the test lead will reach).

Now is the time to fix anything that is wrong.

In the next installment, we will see how to connect the black wire to the tender and complete the installation.

DC vs DCC Locos and Control

It’s about that time of year, when for some reason there seem to be a lot of newcomers to the hobby, and a lot of people considering significant upgrades to their layouts.  Hmm… must be Christmas or something.

One very frequent question I come across, and one which seems to get a lot of answers, some accurate, some not so much, is the question of DC vs DCC control of locomotives, and specifically whether DC locos can be run on DCC track, and DCC locos run on DC track.  I shall attempt, in my rambling and overly-wordy way, to dispel some of the confusion and explain in some detail what is going on and why certain things work and others don’t.

In order to get this done in a blog post instead of a Ph.D. dissertation, I’m going to have to assume you understand some basic electrical concepts like DC and AC voltages and currents.  If you don’t understand these, I would refer you to Wikipedia in the short term, but I do plan to add some blog posts on these basic ideas later on.

Also, I will try very hard not to debate the merits of DC vs. DCC in this blog post, but only to explain (basically) how they work and what happens when you try to mix them.  The debate has long since passed into the “well beaten dead horse” category, anyway.

DC Control

Under DC control, the motor in the locomotive is directly connected to the rails.  It’s a DC motor, so it’s expecting a steady, DC voltage in one direction (one polarity) or the other.  The polarity of the DC voltage on the rails determines which direction the motor (and thus the loco) runs, and the voltage amplitude (level) determines the motor’s speed.  It’s a very simple system, but it works.

The catch is that because the rail voltage is directly controlling the motor, every motor on that set of rails will respond in the same way.  There’s no way to have two different locos running at different speeds or in different directions on the same set of rails.  DC control folks solve this problem by breaking the layout up into several blocks, each of which is electrically isolated from the rest of the blocks.  They use a set of switches to tell which throttle (“cab”) controls which block(s), and make sure that only one train is in each block.

DCC Control

DCC Control is a bit more complex than DC at this level.  In DCC, we put a little tiny computer inside the locomotive.  The computer is responsible for controlling the motor in response from a series of commands from the user’s Throttle (by way of the Command Station).  If you look at what’s happening on the rails, instead of a DC voltage (and polarity) that controls what the motor does, you see something quite different.  What you see is instead, technically, an AC voltage, and it’s quite high – a voltage that would be “full throttle” if we were under DC control.

This is the first major difference between DCC and DC.  In DC, there is always only the voltage required to turn the motor at the required speed, so to make an engine “idle”, you have zero volts on the rails.  Under DCC, there is always full voltage on the rails, no matter what speed the loco is moving.  For N scale and smaller, the DCC rail voltage is usually +/- 12V, and for HO or larger, the voltage can be as high as +/-18V to deliver the extra power the larger scale motors require.

The second major difference is the AC vs. DC part.  Under DC control, for a given direction of train motion, the polarity of the rail voltage is constant.  Reverse the rail polarity, and the train suddenly goes the other direction.  In DCC, the polarity of the rail voltage is always changing, and quite rapidly at that — over eight thousand times a second, in fact.

So keep this in mind.  While the DC rail voltage is a nice steady signal that only goes one direction and for a non-rocket-like train speed probably has a fairly low voltage, the DCC signal is banging back and forth thousands of times a second all the way from a full +12 or +18 to -12 or -18 Volts all the time no matter  what the train is doing.

Why is the signal banging back and forth?  Well, there’s a pattern in that oscillation, and that tiny little computer is paying attention to and deciphering that pattern.  And in that pattern are the commands being sent from the throttle.  Commands like “Run the engine at 50% throttle” or “Turn on your front headlight”, or even “Program CV42 to value 27”.

I could go on at great length about how this all works, but I think this is enough to make my points later on, so let’s move on, in the interest of brevity.

DCC Loco on DC Control

What happens if I buy a brand new DCC-installed loco (or install a DCC decoder in a previously DC loco), and plop it down on my DC-controlled track?  Well, the designers of DCC realized that LOTS of people are going to want to do precisely that — and that they will be very frustrated customers if their new, expensive engines don’t run. So the NMRA DCC standard allows for, and lately decoder manufacturers have been making what are referred to as “Dual-Mode” decoders.  Now,  you may find some older, outdated decoders that don’t do this, but pretty much all current decoders being sold in 2012 support dual mode.

A dual mode decoder is smart enough to realize that it might not be running on DCC track.  So, when power is applied and it wakes up, the decoder looks for a DCC control signal.  If it doesn’t see one, it assumes that it’s on a DC track, and will start following the DC track voltage and polarity as though it were a simple DC motor.  The result is that most modern DCC locomotives will work just fine on DC control, with a few minor caveats.

Caveats you say?  Well, yes, there is one fairly big one.  That little computer inside the decoder needs a minimal voltage to run – usually about 5 volts.  So while your “pure DC” loco will begin to crawl along at 1-2V DC, your DCC-on-DC loco won’t even wake up until a much higher throttle setting.   This is the main caveat.  There may be some other minor ones, but they depend on the specific decoder so we won’t go into them here.

Flying Locomotive Syndrome

There’s one really annoying thing about dual-mode decoders, though, and it’s a big reason why most decoders also have a switch to turn it off.  Every once in a while when you put a locomotive with dual mode enabled on a DCC track, and you power up the layout (especially when recovering from a short circuit), the decoder will mistake the changing voltage on the rails caused by the DCC Booster “waking up” (my term) for a DC signal.  The decoder will then switch into DC mode, and when the Booster starts putting out the regular DCC signal, the loco will race off into the sunset at full speed.  Not a pretty sight.  For this reason, lots of “pure DCC” users like to disable dual mode.

So, if you put your supposedly “dual mode” locomotive on a DC track and it doesn’t work it may be because someone has disabled dual mode.  Just plop it back on the programming track and check bit 2 of CV29.

DC Loco on DCC Control

This is where things get dicey.  If you plop a DC loco down on DCC powered track without doing anything else, here’s what happens.  Remember, the DCC track signal is at full voltage (either +/-12V or +/-18V depending on the booster setting), and it’s changing polarity 8,000 times a second.

Well, your DC locomotive is going to sit there trying to go full speed, reversing direction 8,000 times a second.  It just happens that the nature of the DCC control signal is such that the average time spent at each polarity is about the same, so the DC motor will spend about the same amount of time trying to go both directions.  It won’t really go anywhere, but it will make an ugly buzzing noise while the motor heats up and eventually melts the shell, if the motor itself doesn’t burn out first.

Short answer:  It won’t work.

Digitrax (and others) Address 00 Control

(Note: After learning that Bachmann and Lenz — at least — also provide this feature, I had to re-word this section a bit.  Having a look with a rested set of eyes pointed out a few technical corrections as well.)

NMRA to the rescue — sort of.  In another attempt to allow “backward compatibility”, the NMRA DCC standard allows for a method of controlling a DC locomotive on DCC track.  To my knowledge, only Digitrax has actually implemented this apparently this feature is available from at least Digitrax, Bachmann, and Lenz, maybe others.

They make this work by a method called “zero stretching”.  If you put a DC locomotive on your DCC track, and set your throttle to address 00, you can (usually) control the train.  Here’s how it works.

As mentioned above, the DC motor sees the DCC signal as a DC “full throttle” with a rapidly reversing direction.  It’s a “feature” of the DCC signal that the variations in the signal average out such that the motor doesn’t actually move — that is, the average voltage of that rapidly oscillating DCC signal is zero, because the signal is spending the same amount of time at +12(18)V as at -12(18)V.

When you increase the throttle, the command station starts stretching out some of the “spaces” between commands* so that the signal spends a bit more time at one polarity than the other.  The DC motor will see this as an average voltage somewhat above (or below) zero, and will begin to move.  DCC decoders are programmed to expect — and ignore — this “zero stretching”.  The higher the throttle setting, the longer the stretching time, the higher the average voltage the DC motor sees.

So it works. Sort of.  But it is noisy, and you still have the problem of the idle engine potentially overheating.  So I really don’t recommend it as a regular way to run locos.

Here’s a brief video of a DC locomotive sitting on my Digitrax DCC layout.


By the way, I’m only about 1-for-4 on getting a DC loco to actually move under “address 00” control, but your mileage may vary.

*It’s actually stretching out the length of the “zero” bits within the data, but that’s a detail that really isn’t important at this level of discourse.

DC and DCC side by side

So what does a guy do if he wants to try out or transition to DCC, but he has dozens or hundreds of DC locos, and can’t fork up the $30 each or the conversion time to go whole-hog DCC?  Well, there are some options, but we have to be careful there as well.

DC/DCC Timesharing

One thing you can do is time-share.  Using a DPDT switch, you can wire your DCC booster side by side with one of your DC cabs (let’s say Cab A).  Then, when you want to run DCC locos, clear all the DC trains off the layout, throw all the block switches to Cab A, throw your DC/DCC switch to DCC and go to town.  When it’s time to run DC locos, just throw the DC/DCC switch back, and have fun.  This is really the most practical thing to do.  The only catch here is to be careful not to leave a DC loco idling somewhere on the layout while running DCC.

In short, here, your layout is all-DC today, all-DCC tomorrow, and so on.

DC/DCC Block-Sharing

Another option is to take advantage of the electrically isolated blocks in a DC layout to run DC and DCC trains side by side.  In this case, you wire the DCC booster into one of the cabs as above, and throw only some of the blocks to that cab, such that for example, one loop on the layout is DCC, while the rest are DC.  Some modular layout clubs have taken to doing this, often designating one or more of the loops on the layout as DC, and the others as DCC.

In short, here, the inner loop, or the upper deck, or the left side, or whatever is DCC while the outer loop or lower deck or right side or whatever else is DC.


There is a real danger here.  First, this will only work if your DC wiring system isolates both rails. You cannot properly isolate the DC from DCC if you have a common-rail DC wiring setup.

Second, you must never allow a locomotive to bridge the two regions.  DCC and DC power must never be connected to each other.

What happens?  Two things. First, the DC voltage from the DC throttle will add to the DCC signal (AC voltage) generated by the DCC Booster.  The resulting signal on the rails will look like a DCC signal, but shifted up (or down) by the amount of the DC throttle voltage.  Second, the DC throttle and DCC booster will see each other as “loads”, and will try to feed power into each other.

Precisely what the end result is will depend on exactly how the DCC Booster, the DC throttle, and your DCC decoders are designed.  If the voltage offset created by the short is high enough, it could damage the sensitive electronics in the decoders, “letting the magic smoke out”.  Likewise, if either the DCC Booster or the DC Throttle are unable to “sink” the current being delivered by the other power source, then the output stage of the weaker device will fail.

Most likely the loser in this fight will be the DCC Booster.  If you are lucky, the over-current protection circuitry will kick in and simply shut down the booster.  If you are less lucky, the output drive circuits will be fried (as in — again — “letting the magic smoke out”), and your expensive booster will become an expensive door-stop.

So, if you choose to “block-share” DC and DCC on your layout, I advise that you be extremely careful that there is no way for the two power sources to be connected to each other, including through a locomotive crossing from one region to the other.

Kato Genesis P42 Diesel Decoder Install

Kato P42
Amtrak #188 crosses the road, leading the Cardinal.

It’s been a while since I posted a decoder install how-to, so it’s about time I did so.  A few weeks ago, as a reward for some good news at work, I splurged on one of the Kato P42 Genesis Amtrak train “starter sets”.  The P42 Genesis is a really, really nice locomotive, one of Kato’s best in N scale, by many accounts.  It comes in the set as a DC model, but is very DCC friendly.  Digitrax, NCE, TCS and MRC all have drop-in decoders for the model (the MRC decoder includes sound!), and the install for all of them is quite similar.  In this how-to, we will be installing the Digitrax DN163K0A decoder, but you should be able to adapt this process easily to any of the other brands.

Here’s the locomotive in its packaging along with the rest of the train set (and my daughter’s “pet cow” Bessie).

The starter set

Step 1: Shell Removal

Shell Removed!

To remove the shell, pry the sides apart gently and insert some toothpicks to hold them out.  Pull down on the front trucks (gently but firmly – the trucks will pop out) and lift the shell off in a front-to-back motion.

Step 2: Unclip the motor tabs

Remove the grey clip

Near the center of the frame is a grey plastic clip holding two metal tabs (the motor contact tabs) down.  Gently pry up the clip and set it aside.  You’ll need it again later.  Then bend the two metal tabs up to free the light board.  You might want to take a sharpie and mark the spot where these metal tabs (used to) touch the copper pick-up strips that run under the light board.

Lift the motor tabs clear of the light board

(sorry about the focus on that one!)

Step 3: Insulate the pickup strips

Insulate the contact strips from the motor tabs

I’m sure there’s a more technical term for these, but those two long copper strips that run along the sides of the frame under the light board pick up power from the trucks and deliver it to the light board.  Remove the light board, and then gently lift these two strips out.  With a small piece of Kapton tape, insulate the spot where the motor tabs would touch these strips.  Be sure to insulate all the way around the strip, but don’t use more than one layer of tape.  The fit is fairly tight, and extra tape will make it hard to close things up.  Don’t use regular black electrical tape. it’s too thick, and doesn’t hold up well when heated.  Kapton is the way to go here.

Here’s what the insulated strips should look like when re-installed.

Replace the contact strips. Make sure they’re insulated from the motor tabs.

Step 4: Install the decoder

Install the decoder over the contact strips.

The decoder just drops into place where the light board used to be.  You’ll have to be careful not to dislodge the pick-up strips.

Step 5: Re-clip the motor tabs

Replace the grey clip. Press hard. Some extra tape might help.

Bend the motor tabs down so they contact the pads on the decoder.  Make sure they do not contact the pick-up strips!  Replace the grey plastic clip to hold the strips in place.  You have to press pretty hard to get the clip to snap in firmly.  If the clip is broken, or if you want to be extra-sure, you can solder the tabs to the decoder.  An extra strip of tape over the clip is also good insurance.

Step 6: Bend down the headlight

Bend the front LED down at an angle.

The last thing to do before re-installing the shell is to bend the front LED to about a 30-45˚ angle.  This helps make sure the LED fits into the light guide in the shell.   Once that’s done, slip the shell back in place, install the extra parts provided by Kato, and enjoy your locomotive!

Here’s a “wide shot” of the completed install:

And, of course, some video!


Help! My Zephyr Isn’t Working!

In a recent thread on my favorite internet train watering hole, one of the users, having just received his new Digitrax Zephyr Xtra and a couple of new DCC locomotives, was having trouble using the Zephyr to program the locomotives.

The jolly crew of course jumped in to help him diagnose the problem, and what resulted was a pretty good list of things to check before hitting the panic button when you DCC conroller doesn’t work.  While these points are specific to the Zephyr and Zephyr Xtra, most if not all of them are also applicable to most DCC systems.

  • Is it wired up correctly?  The main layout should be wired to the “Rail A” and “Rail B” terminals, the programming track to “Prog A” and “Prog B”.  Beware that there is a ground terminal between the two programming track terminals.
  • Where is the locomotive, and which programming mode are you using?  Ops Mode works only on the main track, while Direct and Page Modes work only on the programming track.
  • Is it a non-Digitrax decoder?  Some non-Digitrax decoders don’t respond with a strong enough signal for the programmer to “hear” the response.  Placing a 1-kΩ resistor across the rails can help with this.
  • Are the rails and locomotive wheels clean?  Poor contact can affect the communications.
  • Does the locomotive have  a decoder?  Sometimes it pays to check the obvious.
  • If using a PR3 and JMRI with your Zephyr, did you tell JMRI to use the PR3 in MS100 mode or Stand-alone Programmer mode?  Stand-alone mode should only be used if the programming track is wired directly to the PR3.
  • If you’re in Ops Mode, did you select the correct locomotive address?

Well, that’s a start.  My hat is off to my friends at nScale.net for their willingness to help those with questions, and to their suggestions of things to check.

If you have ideas to add to the list, be sure to post them here!

Bachmann F7A/B Decoder Install

Untitled by BGTwinDad
Untitled, a photo by BGTwinDad on Flickr.

I just completed this install of a pair of TCS M1 DCC decoders into a Bachmann Spectrum F7A/B set. This was a challenge because it required some milling of the frame to make room for the decoder and to isolate the motor. Still, it wasn’t all that hard, so if you’re looking to expand your skills into installs that require frame mods, this might be a good place to start.

I was so excited to get this one back to its owner that I forgot to take some “pretty shots” of the pair, so you’ll have to make do with the test-track photo above.  This pair was in Southern Pacific livery, and was a fairly nicely detailed, smooth running pair.  The Spectrum line from Bachmann is a big step up from their train set models, and is generally a good value buy for the cost conscious.  While the design is not “DCC Ready” in the sense that a fair amount of work is required to hook it up, at least it has a split frame and the mods required are minor and straightforward.

The A and B units share the same chassis, which makes the B unit a bit easier since the decoder will easily fit into the chassis cut-out for the A-unit cab.  Plus, there’s no headlight.  Tim “diezmon” Diez provided an excellent tutorial on the TCS website for the B unit, and for the most part I simply followed his instructions.  I highly recommend you review that page, as I will mostly be detailing the variations I made from that plan.

My B-unit install...

The B unit install went exactly as Tim outlined it, and aside from the juggling act required to reassemble the frame went very easily.  To attach the red and black wires, I drilled a small hole in the top of each frame half and miraculously managed to solder the wires into the holes.  I don’t recommend this method.  Much better to drill, tap and screw the wires to the frame.  Fortunately, the MicroTrains #1059 coupler drill and tap set – and the screws included with the 1015 couplers – work very well for this application.  You do have to cut the screws short, though.  I think the screws are available separately if you want them.  Another method that a local modeler tipped me off to is to wrap the wires around the frame mount screw bosses.  I haven’t tried this but maybe it would work.

The frame I had was slightly different than Tim’s in that the bottom motor brush contact was a spring compressed between the motor brush and the side of the frame.  I’m not sure that milling out the bottom of the conductor-side frame is necessary on those models, but it is easy and probably good insurance.  You will definitely have to mill the tab Tim marks off the top of the Engineer’s side frame.

The A unit requires a little bit more work.  First, there really isn’t room beneath the cab for the decoder, so I milled out the opening above the rear truck gears to slip the decoder in.  This also allowed me to replace the headlamp with a 3mm LED.  I’ll contradict myself here by saying that if you retain the incandescent lamp, or if you use an SMD LED, you *might* be able  to squeeze a small decoder into the cab area.

The milled out space for the decoder...

Aside from milling space for the decoder and installing the LED, the install goes exactly like the B unit.

Installing the LED is simple.  You’ll need a warm white LED, available from a hobby supplier like Richmond Controls (the one I used), or from an electronics supplier like DigiKey or Mouser Electronics.  You’re looking for something in the 3000K color temperature range.  Higher temperatures will have a more bluish tint that will not replicate the old headlamps very well.  You’ll also need a resistor.  The value is not terribly critical, as long as it is above about 600Ω. I used a 1KΩ resistor and found it plenty bright.  You simply connect the blue wire to the resistor, the resistor to the anode (positive terminal) of the LED, and the cathode (negative terminal) of the LED to the white wire.  You can also put the resistor in the white wire instead, which is what I did.

Wiring the LED and resistor...

It is critically important that you get the polarity of the LED correct.  The cathode is the shorter pin on a radial-lead LED, and will also be nearest the “flat spot” in the LED case.  On a surface mount LED the cathode will be marked with a dot or other marker.  The cathode must be connected to the white wire, not the blue.

You will also have to clip the leads short on a radial-lead LED to make them fit.  This is where knowing about the flat spot is useful.  The LED does not go in the hole where the original lamp went, but simply lays horizontally over the front truck in the cab area.  You may want to use some opaque material to block the LED light from entering the cab.  My friend liked the glow of the lit cab, so we omitted this step.

Once you have everything wired up, all you have to do is tape it down and slip the shell back over the frame.  Both units have strips of black tape along the sides that provide a black background to the side windows.  I forgot to remove these before milling, so I got the sticky side all covered with metal fragments.  Instead of replacing the tape with more black, I used Kapton tape, which I think gives a better “see-through” appearance to the windows.  Beauty is in the eye of the beholder, though, so feel free to use black, or to carefully remove and re-use the factory tape.

As should be expected, this procedure will work not just with the TCS M1 decoder, but with any similarly sized NMRA-compliant wired decoder.  The Digitrax DZ125 would be a good alternate if you prefer that brand, as would the NCE N12-SR.

Additional photos and a few more details are available on my Flicker Set.

Model Power 4-6-2 Decoder Install

Untitled by BGTwinDad
Untitled, a photo by BGTwinDad on Flickr.

Over the last two weeks or so, I have been working to install a Digitrax DZ125 decoder into the tender of a Model Power N-scale 4-6-2 “Pacific” locomotive.  This was a “commissioned” job for a friend, who had the locomotive and decoder shipped directly to me from the store, and I will be forwarding it on to him shortly.

Even though I was using a Digitrax decoder, the installation instructions from the TCS website submitted by Jeffry Maurer of Sacramento CA — thanks, Jeff! — are perfectly suitable.  Jeff used a TCS MC2, I used the Digitrax DZ125.  I’m quite sure a TCS M1 or any other small hard-wire decoder would work just fine and install in the same way.  The tender is a bit cramped if you leave the weights in place, so you’ll want to use a small one.

(Note that Jeff claims that this install will also work for the Model Power 2-8-2 “Mikado”.  I can’t prove this but I have no reason to believe it won’t work.)

The basic decoder install is very straightforward, but the lighting update was a bit tricky.  Model Power has set this locomotive up to be “DCC Friendly”, and it is.  Power from the drivers is passed back to the tender via a red/black wire pair across the drawbar, combined with power from the tender wheels, and then returned to the motor in the boiler via  a separate grey/orange wire pair.  This little bit of extra wiring work on their part makes the decoder install very simple.

Inside the tender "Before" ...

To add the decoder, all you have to do is remove the tender shell, clip the grey and orange wires free from the black/red wires, and solder the color-matched wires (grey to grey, orange to orange, red to red, black to black) of the decoder to the tender wiring, tape everything down, and replace the tender shell.  Anyone with even a little bit of soldering skill should be able to do this much.

Inside the tender "After" ...

At this point, though, the (incandescent) headlight is still directly powered from the rails via contact strips on the driver axles.  It cannot be turned off, and will be fairly bright.  If you want DCC control of the headlight, we’ll have to do some minor surgery.  On this particular model, I decided to replace the incandescent bulb with a 1206 size SMD (surface mount) LED.  Unfortunately, I failed to take very many photos, so you’ll mostly ave to take my “word” for it.  The good news is that the instructions provided by Jeff above are exactly what I did with only a few very minor modifications.

The basic process is as follows:

  1. Separate the boiler and cab from the locomotive drive train
  2. Clip off the contact strips from the headlight assembly
  3. Solder two wires to the headlight and run them back to the tender
  4. Attach the wires to the blue and white decoder wires
  5. Reassemble the loco.

I found only one minor variation to Jeff’s procedure, and that is that apparently on the version of the model I have, the cab is not a separate piece, but comes off with the rest of the boiler.  Other than that, the process is the same.  Instead of painting the decoder wires black with a Sharpie, I cut the blue and white leads short and replaced them with lengths of black wire.

I also only had to make a few minor changes to swap in an LED as well.  First, back in the tender, I added a 1KΩ resistor on the blue wire.  This limits current to the LED and protects it.  Second, you replace the lamp with the LED, making sure to keep the polarity correct.  The cathode (“negative”) terminal of the LED is usually marked with a dot or other mark, and this should go to the white wire, while the anode (“positive”) terminal goes to the blue wire.  Keeping this straight is especially important if you have replaced the decoder wires with black wire.  To be sure of this – and to make handling the LED a bit easier, I soldered short lengths of blue and white wire to the actual LED pads, and then connected these blue/white lengths to the long black wires back to the tender.

SMD Led with blue and white leads attached...

One other change.  The headlamp (mounted on the drive frame) sticks up through a hole in the bottom of the boiler.  To get the 1206 size LED and its wires to fit, I had to square up the hole just a bit with a needle file.  I did so just enough so that the LED now press-fits into the hole in the boiler instead of mounting to the frame.

LED installed in the Pacific boiler

The basic decoder installation is very easy, assuming you know how to solder wires together.  A reasonable level of care and attention to detail will do fine here.  Connecting the headlamp up requires considerably more work, but even so, most of the trouble is mechanical – routing the wires unobtrusively beneath the running boards, removing the incandescent lamp, and reassembling the engine.  Having completed this one I concur with Jeff’s assessment, if an easy drop-in is a “1”, then the basic install is a “3” and the headlight work is a “6”.

Decoder Install: Intermountain F3A

In this installment, we’re going to tackle another “easy” DCC decoder install.  Not quite as easy as the Kato NW2, but still very much a beginner project.  Today, we’re going to install a TCS IMF4 decoder into an Intermountain F3A locomotive.

This particular locomotive was a gift from a friend.  It’s an excellent runner, but happens to be missing a headlight.  We’ll discuss what to do about the headlight, and I will show its installation in another post as soon as the replacement arrives, but I won’t be able to show that step here.

You will need a soldering iron and solder, and you will need some insulating tape.  Kapton tape would be the better choice, but regular vinyl electrical tape is OK. Do not attempt this installation without a small piece of insulating tape.

OK, let’s get started, shall we?

Step 1: Remove the shell

The first step to remove the shell is to remove the front coupler.  Flip the locomotive upside-down, and remove the screw holding the coupler in place.  Put it somewhere safe!  Then pull the coupler straight out the hole in the pilot.  Store it somewhere safe as well.  You don’t have to remove the rear coupler.

Next, flip the engine upright and carefully lift the shell off the chassis.  Spread the sides apart a bit at the fuel tank with a pair of toothpicks.  Lift the cab end off first, and it will come off rather easily.

Step 2: Disconnect the LED

If your engine has a headlight (it should!), it will be nestled into the black tubing at the cab end of the loco, and two wires will extend back and be soldered to the light board where shown in the picture.  Take a note of which color wire is attached to which terminal on the board.  Better yet, take a photo so you can refer back to it.

With your soldering iron, melt the solder and disconnect the two wires.  Pull the wires back out of the way, but do not remove the headlight.  If you want to replace the headlight LED with, say, a different color or intensity, now would be a good time, though.

Step 3: Remove the light board

In the photo above, you’ll see that the light board is held in place by two screws.  Remove the screws (save them!!) and lift the light board out of the depression in the chassis.

Side Note:  Why you need insulating tape!

When I was preparing to do this install, a friend cautioned me that I would need some insulating tape.  He had learned “the hard way” by frying a decoder and taking advantage of the generous TCS no-questions-asked warranty.  From the install photos I had seen, I did not see why this would be necessary.  After all, wouldn’t the DC light board also need insulation?

Here’s why:  As you can see from the photo below, the back side of the light board (left) has no exposed circuit traces.  The board itself insulates the simple DC circuits from the frame.  The TCS decoder (right), however, has circuit traces and via holes (holes that provide an electrical connection between the two sides of the board).  These via holes would short to the frame if an insulator isn’t provided.

I am not certain why TCS does not provide a piece of insulating material to slip below the board, but it is definitely needed.  Kapton tape would be an excellent choice, but is relatively expensive and hard to find.  You can order it online from various sources (Grainger, Mouser.com, DigiKey, etc.).  Regular vinyl electrical tape will work, as would a carefully cut-to-fit piece of cardstock.

Step 4: Insulate the back side of the decoder

Before installing the decoder, you must insulate the back side from the frame.  Cut a piece of insulating tape to fit between the two posts for the motor brushes and the mounting screw hole on the far end.  The piece should be about 1/2″ wide by 1-7/16″ long.  It is OK if it wraps up around the sides a bit, but you must make sure it does not cover up the mounting hole in the corner nor the motor brush posts.  It must cover all of the other exposed metal on the back of the decoder board.

If you prefer, a thin piece of cardstock cut to fit under the board will work, but it must be thin enough not to interfere with the contact between the motor brush tabs and the posts on the decoder.

Step 5: Install the decoder and attach the LED

We’re almost done, but now you will need your soldering iron.

Before installing the decoder, slip another small piece of insulating onto the frame in the area where the LED wires will be – the cab end, that is…

Drop the decoder in place on top of the chassis and screw it in place.  Solder the headlight LED wires to the board on the two pads indicated in the picture (Note: the picture above is rotated relative to all the previous photos.  The cab end is to the right in this picture).  BE SURE to attach the wires in the same relative orientation as they were before you removed them from the light board.

Step 6: Reinstall the shell and front coupler

Slip the shell back over the chassis.  Then flip the engine over, re-insert the coupler through the front of the pilot and screw it to the chassis the same way it was before you started.

I found it helpful to slip a flat-head screwdriver between the coupler draft box and the front truck to help keep it square to the front of the locomotive while tightening the screw.  Otherwise the box will tend to turn with the screw, leading to a misaligned coupler.

And there you have it!  A DCC-powered Intermountain F3A.  The installation should be almost identical for the Digitrax DN163I1C, and also just the same for the F3B and F7A/B from Intermountain, all of which share a common chassis.



Decoder Install: Kato NW2

This should be a long post, but not too long.  We’re going to install a TCS K3D3 DCC decoder into a Kato NW2 N-scale locomotive.  The Kato NW2 was designed to be DCC-ready, and the TCS K3D3 is a drop-in design, so that makes this a very easy, 15 minute or less install.  If you have one of these nice little switchers, you should not fear this task at all.

This install procedure should also work for the Digitrax DN123K3, which is also a drop-in replacement for the Kato NW2, though I haven’t tried it myself.

Let’s get started, shall we?

Step 1: Remove the shell

The shell is basically press-fit over the chassis.  To remove, simply pull gently but firmly down on the trucks and it should slide off.  It may help to spread the shell just a bit with a toothpick on either side, but I can generally nurse mine off with some steady pressure.

Once the shell is removed,  you’ll be able to see the light board on top of the chassis, with the two tabs that connect the light board to the motor brushes (round things in the center of the chassis sides)

Step 2: Remove the motor clips

Next up, we need to carefully remove the motor clips.  These are the little metal things that look like frogs hanging from the light board with their legs wrapped around the motor brushes.  Before moving forward, study how the clip is attached to the light board and the motor brush.  Take a photo or two if it helps you.  You will reinstall the clip onto the DCC decoder exactly the way it is here.

To remove them, take a toothpick or a jeweler’s screwdriver (or tweezers) and gently pry the clip from around the brush.  Be careful, and don’t bend the clip out of shape, as you will need to replace it later.  The clip is springy, so it should pop off with some gentle pressure.  Once the “frog’s legs” are free of the motor brush, gently but firmly pry the clip from the light board and set it aside for use later.  Repeat on the other side.  The clips are identical, so don’t worry about getting them mixed up.

Step 3: Remove the light board

The light board is the circuit board on top of the chassis.  It is tightly held down by tabs in the top of the frame.  To remove, you must push it forward until it slides free of the tabs.  Squeezing gently on the bottom of the frame may help a bit.  Mine was very tight (a good thing), but with firm, steady pressure, it will slide forward and come loose.  I used a screwdriver blade as a pushing tool.  Probably not smart, as it may well have slipped and damaged the LED on the end of the board.  Better to use something a bit larger and more blunt, and less likely to slip.

Once you have slid the board free of the tabs, it can be lifted from the chassis and set aside.  I kept mine, but there’s not much reason to.

Step 4: Install the Decoder

To install the decoder, you simply place it on top of the chassis and slide it back under the tabs.  A couple of details, though.  The “body” of the TCS decoder is just slightly longer than the space between the tabs, so it won’t lay flat like the light board did.  To get around this, tip it up slightly and “tuck” it under the rear tabs just a bit, as shown above.  It will then lay flat and you can slide it into position.  It is a very tight fit (like the light board was), so you will have to press firmly to slide it into position.  Again, squeezing the bottom of the frame slightly seemed to help.  Finally, you can push the board in too far.  Try to align the clip contacts directly above the motor brushes so the clips will install easily.

Step 5: Reinstall the motor clips

Next we must reinstall the motor clips.  Press the clips directly onto the clip tabs, just like they were on the light board, and then snap the “frog’s legs” around the motor brushes.  Make sure everything is lined up straight, and you are almost finished.

Step 6: Reinstall the Shell

This actually turned out to be the trickiest part of the install.  For some reason, when removing the shell on my NW2, the cab detail part tends to drop out of position.  When that happens, the chassis won’t go back in exactly right, and it’s not immediately obvious why.  Here’s what the cab detail looks like from underneath when it’s loose…

And here’s what it looks like when it’s been pressed back into its correct location…

Double check this, and then slide the shell over the chassis until it snaps into place.  Congratulations!  You’ve just installed a DCC drop-in decoder in your Kato NW2!  You can now take it over to your programming track and customize it, or drop it on your layout and have fun!

This is a very simple install, about as easy as it gets.  If I weren’t stopping to take pictures and notes, and talking with two very excited kids, I could probably get it done in well under 10 minutes.  As it was, going very slowly with distractions it took 17 minutes total.  With this install, there’s no soldering, no wires, no insulating tape, no tricks at all, and you get a nice, smooth running loco “out of the box.”

If you’ve tried this install and have comments, questions, or ran into problems, feel free to share them here!