This week’s post will be a continuation of my step-by-step build of an N Scale A-B-A ready-to-run set of Alco C-855 locomotives.  And this post will be concentrating on fitting DCC decoders to the modified chassis.  You can find part one of the build here.

Although this post is aimed at DCC installation the first part is also relevant to DC operators.

The chassis, as you can see below, is held together by vertical bolts which clamp the top and bottom sections together.  But the bolts also do more than that.  Instead of a nut on the bottom the bolts screw into the plates which hold in the trucks, and in turn convey the power into the chassis.  The bolts nearest the front of the picture and on the left hand side of the locomotive connect the left power pickup to the top chassis section.  The bolts furthest away and on the right hand side are isolated in plastic sleeves and connect the right power pick up to the lower chassis section.

When these models were new they had a grain-of-wheat bulb connected to the front bolts which was used for the headlight, and illuminated the cab!  But we can now use these as power connections for the DCC decoder.  The original bulb had a diode attached so it wouldn’t operate in reverse.  Con Cor soldered the bulb wire to a tab plate under the bolt head and twisted the stiff diode wire under the other.  As I want to ensure good contact between the chassis and decoder I’ve made another solder tab for the other bolt as can see below.   I made it from an old axle wiper taken from a scrapped locomotive.  The decoder, also shown below, is an N scale sized chip from Gaugemaster but any DCC decoder will work as long as it fits.

Now, before we start with the decoder some electrical bridges need to be added.  This is the part which also needs to be done for DC operation.  In the picture below you can see I’ve linked the two right hand side bots together as well as the left.  This is because where the chassis has been cut and extended the new glued joints can form an isolating barrier.  So if the decoder was simply connected to the two front bolts it wouldn’t receive any power from the rear truck.

The center sections will also be isolated and as the motor used to collect power by having the contact simply touching the chassis, it’ll no longer work.  So the motor wires I’m about to install for DCC will also need to be connected for DC but just back to the solder tabs.

For the DCC decoder the red and black wires are cut short and soldered directly to the solder tabs. They should now be linked to both sets of trucks.

The chip can then be folded in and secured with Kapton tape.  Kapton tape is ideal as it’s isolating, thin, strong and designed to withstand heat in electrical situations.

The gray wire is the bottom motor feed and runs outside the chassis and is soldered onto the bottom motor tab.

There is a wire channel printed into the chassis extension for this wire as you can see below.  This wire, once fitted can be covered in a piece of Kapton tape or glued in.

The orange wire runs halfway down the other side and connects to the top motor tab. It could go through the hole in the top but I like to do it this way.  The blue and white wire are for the headlight so stay at the front.  If you wanted to add a rear light the yellow and another blue would need to be run to the back but as these will run in an A-B-A consist the rear light is not necessary.  With all the wires connected, except for the head light wires which I’m going to cover in a later post, they can now be fixed down.

Again I used Kapton tape to hold the wires down.  It’s important to position the wires in the middle of the chassis as they run from one end to the other as the shell has feet which sit on top of the chassis.  But there’s a gap in the middle of the foot to allow the wires to pass.  The two strips of Kapton tape are where the feet sit.

The chassis is now ready for DCC testing.

The next step is to fit the shell and for that I have to finish painting it which I’ll cover in a later post.