An Athearn Diesel
Makes A Good First
Decoder Installation

Why is an Athearn locomotive a good first choice? Because they are fairly simple internally and most of us who've been in the hobby for some years have a few of them.

Many model train enthusiasts I've met over the years are afraid of electricity and are scared of tackling electronic projects like a decoder installation in an Athearn locomotive. I know. I was one of them. One of the charms of model railroading is the sense of accomplishment we get when we succeed at something we were avoiding for fear of failure.

Installing decoders terrifies new model railroaders and many veterans. Let alone changing the CV values after they're installed. CVs? Hexidecimal? Bits and bytes? You've got to be kidding!

But I have about 40 locomotives, both steam and diesel. My oldest is a Mantua Mikado from the early 60s. A couple of growling Hobbytowns that don't need sound they're so loud. A mixture of brass and non-brass: Tenshodo, Atlas, Proto 1000s, Proto 2000s, Model Power, Atlas, Athearn, lots of Athearn engines.

First of all, some of these never run on the layout. They sit on shelves or sleep in boxes. Some are just plain cranky. Some only need a good cleaning and lubrication. Some don't track very well.

  • Rule 1:  Concentrate on the engines you really would like to run.

Unless you have a big club-like railroad, or a sophisticated computer-controlled mainline, you'll seldom run more than a few engines at a time, even when your friends come over. And there are probably just a couple of engines you really like to run. 

So what does it matter if you take an older engine you seldom use and try to install a decoder?Even if you blow up a decoder by shorting it out, most DCC manufacturers are very forgiving about replacing your first one at least. After all, they want you to succeed because they want your business. I destroyed one of my first decoders and Lenz was quick to replace it without a hassle.  

  •  Rule 2:  You'll never know if you don't try

One of my first attempts. An older Athearn diesel switcher with a Lenz decoder.
Athearn decoder install

I chose an old Athearn switcher that was gathering dust. It had been painted in my Utopia Northern livery in another burst of creativity overcoming fear of  airbrushing. Here it is with the shell removed and the decoder installed.



  •  Rule 3:  Get it running well on DC before proceeding.

I had experimented with Ernst regearing in this locomotive but I was never happy with the result. Of course, with DCC, you can simulate regearing electronically by changing CV values. However, the engine needs to run OK. I took the engine apart, cleaned and lubricated everything.

  • Clean and polish moving parts. 

Use a Dremel steel brush, sandpaper or file to thoroughly clean any paint or rust away from the bolster pin. Often this is where electrical pickup is compromised. Clean the wheels, too. Use a Que-tip dipped in alcohol (not soaked) to clean the commutator shaft. Let it dry.

  • Carefully remove retaining clips.

 Pop off the top and bottom spring clips. Careful. Don't lose the springs. They can fly across the room. Check to make sure the graphite (I think they're graphite) slugs that rub on the commutator aren't too worn. You can buy replacements. You'll notice that the top metal strapping that transfers track power to the motor has been removed and replaced with wire. This is far better than relying on the mechanical rubbing together of the two surfaces.  You're also better to replace the lights so don't worry about cutting off the strapping and the posts from the bolsters.

  • Drill the frame to attach wires.

 I drill the side frame in some convenient location with a #80 drill, tap the hole, and insert a round head screw with a washer.  Drill slowly so as not to break the drill. When tapping, only twist a quarter turn each time, back out the tap and clean it before going deeper. Use cutting oil or whatever oil you have. The metal is soft ans easily binds drill bits and taps.Solder the wire from the truck to the washer. Make sure the shell will clear.

  • Isolate the motor. This is critical.

   The motor brushes MUST be completely isolated from the rail pickup. 

 You can drill and tap the post from the bolster to route power from one side of the trucks to the decoder. On an Athearn locomotive with the original motor, you need to pull the motor out, flatten the clip that is used to pick up power from the frame, and then reinstall it with some kind of insulation between the motor and the frame.

  • Don't use black electrical tape.

Common black electrical tape gets sticky when hot. 3M makes another kind of tape that is better. Or use some very thin styrene or carpet tape.

  •   Choose a basic decoder for your first installation.

You don't need to get fancy yet. Forget about ditch lights, strobes, and other esoteric features. I used a Lenz LE1024W back EMF DCC decoder because I happened to have bought one. Back EMF is a technical way of adjusting the motor's voltage to keep the rotation speed nearly constant to make the engine run more smoothly, especially on grades and at slow speeds. Great for yard assignments. 

 Manufacturers tend to discontinue decoders as electronics in the hobby improve. Lenz now has some silent decoders and a series designed to work better on dirty track. Other manufacturers offer a range of choices.  The important thing is to buy a decoder that follows NMRA standards. Many of the newer decoders have features the average model railroader will probably never use.

  •  Choose a decoder that is going to fit.

Size is very important, but the smaller decoders may not handle the amperage your locomotive draws. Old Athearn engines with open frame motors (and brass DC engines) draw more current than coreless motors. I have used Digitrax N scale decoders in a few installations but not in an Athearn locomotive. Ask at your favorite hobby shop or email the manufacturer for a recommendation. Explain it is your first installation. You can always pay the hobby shop to do it but what fun is that? You're in this deep already, keep going.

Some of the features you want (that this Lenz decoder has) are:

  • Selectable for operation with 14/27, 28/55 or 128/256 speed steps. 

I usually use either 28 or 128. The difference? The higher number 128 provides smoother speed control over the range.  

  • Provides 1 amp continuous motor current.
  • Programmable locomotive address with support for extended addressing. 

The recommendation by the pros who know such things is to check the stall current by holding the DC engine on the track until the wheels won't turn and then verify the amperage draw with a meter. I have never done this. I have never had a problem even with an old Athearn original motor. (If you're installing an N gauge decoder in an HO engine to save space you'd probably better follow the experts' advice). This locomotive carries the number 60 so I don't even need 4-digit addressing.  There are a whole bunch of other features I'll probably never use, like single Strobe, double Strobe, adjustable blinking, etc. I just want the headlight and rear light to work when I change direction. Again, let your pocketbook rule.

Headlights

Tip: Yeloglo White LEDs from Miniatronics are an excellent choice.The ultra bright 3mm dia. 3-4 VDC LEDs that simulate incandescent bulbs were recommended to me by Paul at Credit Valley Railway Company in Streetsville. It's helpful to find someone or a hobby shop to turn to when you run into trouble. The package of LEDs comes with resistors. Follow the decoder's instructions for which ones to use.

Tip:  I like using LEDs because the heat from miniature 12-14 volt bulbs can melt plastic. I have a bubble behind the smokestack on my Proto 2000 USRA 0-8-0 steam locomotive due to this problem even with a piece of tin foil as a heat sink to disperse the heat.

Let's go all the way and hardwire this loco!

If your engine can use an NMRA 8-pin socket, great. But you wanted to learn, right? So let's take it one wire at a time.

Wiring to the decoder follows the NMRA convention. The standard is:

  • red wire to right rail pickup 
  • black wire to left rail pickup
  • orange wire to the motor terminal that was previously connected to the right rail
  • gray wire to the motor terminal that was previously connected to the left rail
  • blue wire is common for the headlights
  • white wire to the front headlight
  • yellow wire to the rear headlight

The Lenz LE1024W has a few other wires and light options. Just follow the instructions for whichever decoder you buy.

If the engine runs the wrong way after installation, you can either reverse and resolder the orange and gray wires to the motor or change it with the software.

  • Rule 4: Use heat shrink tubing.

You have to make sure you don't accidently cause a short when you squeeze the shell back on. Pick up some 1/16" heat shrink tubing in assorted colours from Railtronics. Most good hobby shops carry it. You can usually find tubing at RadioShack (The Source in Canada) but the packages have assorted sizes, many of which you'll never find a use for. I buy it at Sayal Electronics in Barrie, Ontario.

  •  Rule 5: Add weight.

You'll notice in the photo that the original weight has been removed to make room for the decoder. This is often a compromise when reworking an older locomotive. I've stuffed some weight into both ends of the shell. Where possible, distribute the weight above the trucks.

  •  Rule 6: Test the engine on the programming track.

Make sure it works correctly before putting the shell back on. This is where you avoid sending it back to the manufacturer for a replacement. It is also where you avoid disappointment and get that first thrill of success. If the decoder is installed correctly you will be able to read back the factory pre-set address 03. Now put the shell on.

  • Rule 7: Retest the engine on the programming track with the shell on.

Just in case the heat shrink tubing isn't isolating everything or the decoder is pressing on some metal part. It can happen!

  • Rule 8: Retest the engine on the programming track with the shell on. 

Actually, #8 isn't a rule. There are no more rules. I only want to stress the importance of the programming track. I just like that extra margin of comfort. It's time to put your engine on the mainline and power up.

This may sound silly but make sure your layout is turned on and the DCC system is working properly.  At the time I had two main AC power bars. One turned on the layout and the relays, etc. but did not turn on the DCC power. I spent a good 15 minutes hunting for a problem before I realized the system wasn't turned on.

  • Remember this rule. Start with the simplest solution first when troubleshooting.

Now you can go back to the programming track and play with changing CVs.

The first ones you'll want to experiment with are:

  • CV1 locomotive address
  • CV2 Start voltage (I had to reset this to 6 or 7 for this engine)
  • CV3 Acceleration momentum
  • CV4 Brake momentum

Having fun yet? That wasn't really too hard, was it? Now you can tackle some of the more tricky installs. This next one is a little tougher becaue the body shell is narrow. Go to Digitrax sound decoder installation in an Atlas RS3.



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