This week’s post is a guest post; I had one of these before from fellow N Scale modeller Mike Musick who wrote an article about improving Con-Cors N Scale U50s, Turbines, and my C-855 by replacing the wheel sets.  This time the article has been written by N Scale modeller Chris Hatt who has written about installing ESU LokSound Select Direct Micro DCC decoders into N scale Kato Locomotives.

So without further ado, I’ll hand you over to Chris.

LokSound Select Direct Micro DCC (part number 73100)

So, ESU recently released to market three new decoders designed to fit in N-scale “Narrow Hood” locomotives. These are locomotives such as the EMD “SD” locomotives (SD40/50/6070/80 and 90 series) and the GE Evolution (ES44 series), AC4400 and Dash-9 type models which have an external walkway down each side rather than a full-width body shell. The body shells on these models are typically around 10mm wide inside.

The LokPilot V4 Direct Micro OEM (#54650) and LokSound Select Direct Micro OEM (#73199) are both designed to partner recent locomotives from InterMountain and Atlas and are available factory fitted or aftermarket to retrofit DC models. The one of interest to me is the LokSound Select Direct Micro (#73100). This is designed to “drop into many pre-2016 Atlas and InterMountain locos, (and others with minor modification)” (http://www.esu.eu/en/products/loksound/loksound-select-direct-micro/). Many people have been asking on-line if they will fit into Kato N-scale models and there have been few answers. As most of my locomotives are Kato and I favour using LokSound decoders to install sound, I decided to find out.

So what do you get?  In the blister pack is the decoder, two 3mm golden white LEDs and two lengths of fine brown-insulated wire for connecting a speaker of your choice. The card backing of the blister pack is a fold-out instruction sheet (the LEDs and wire are between the halves of the card in a zip-lock bag, not in the blister).

Figure 1: The 73100 from the top. The front-end is to the left.

You will note that there are five pairs of metal pads along the edges of the 73100. The two pairs nearest each end of the decoder are frame power pickups, red to the top of the photograph and black below. The pair nearest the center on the narrowest part of the decoder are not labelled on any documentation but careful investigation with a continuity tester showed that these are duplicates of the motor power pads on the underside of the decoder. The pair of pads inboard of the seconds power pick ups from the right are the speaker connections. The tiny yellowish rectangle on the centre-line at the left end is a surface mount 0402 LED connected to output AUX1. This LED is around 1.0mm x 0.5mm!

Figure 2: The underside of the 73100. The front-end is to the left.

The two big pads under the decoder are the motor drive outputs. The front-most is the “orange” output touching the right-hand side of the decoder. Near the back of the decoder are a +ve supply (DCC “blue”) pad and pads for the AUX3 and AUX4 function outputs. At each end of the decoder are a pair of pads spaced for soldering the LEDs for the head- and tail-lights (F0F and F0R). According to the instructions, there are current limiting resistors installed on all the outputs and standard LEDs can be soldered directly to the pads. The supplied 3mm LEDs are not attached so that you can cut the leads to the right lengths to position them appropriately for the model that you are installing the decoder in.
The tiny yellowish rectangle on the centre-line at the right-hand end is another surface mount 0402 LED connected as AUX2. It will be very difficult to desolder the AUX1 and AUX2 LEDs and reuse the pads, so while this is technically a six function decoder, two of them will be nigh on impossible to exploit unless it is possible to pipe the light using optical fibre.

How does it compare to a Kato lighting PCB?

Figure 3 shows the 73100 alongside the lighting and power PCBs from several Kato models.

From top to bottom:
• The PCB from an SD80MAC (also used in the SD9043MAC).
• The 73100.
• A PCB from an SD70MAC (also used in the early-SD70M, ES44AC, AC4400CW, and several others) .
• The revised PCB used in the “screwless” later-SD70M and the SD70Ace. This board has sideways-facing surface-mounted LEDs in place of the 3mm discretes on the SD70MAC board.

All four have the front-end of the board to the left.  Putting the decoder in my micrometer, it measures 0.75mm thick compared to the 0.5mm of the Kato PCB.

Fitting the 73100 in a Kato early-SD70M frame.

The 73100 is closest to the early SD70M/SD70MAC/ES44AC/AC4400CW part so I started there.

Figure 4: The 73100 offered up to a Kato SD70M frame.

Offering the 73100 up to the frame, it becomes obvious that the increase in width of the board at the rearmost but one pair of power pickups means that the decoder will not fit between the frame halves without easing back the blocks indicated in figure 5 below.

Figure 5: Easing the fit of the waist of the decoder.

Shaving off about 0.5mm from each side with a file, Dremel or milling machine ensures clearance. It does not matter if the fit is snug enough that the pads touch the frame because the exposed pads are frame power pickups.

Figure 6: This nub needs to be made smaller.

The slightly thicker board of the 73100 means that the rounded end of the nub shown in figure 6 that presses on the contact pad at the front of the decoder needs to be trimmed slightly. While the decoder will not drop-and-slide-in like the PCB, it can be trapped between the frame halves as they are assembled and it make good contact and is firmly fixed fore-and-aft.

However, powering up the decoder in the frame caused it to go into a rapid short-circuit/shut-down cycle as shown by blinking of the AUX1 LED. Oops!

Careful inspection showed that there were a number of surface-mounted components that could foul the frame halves and pass track power into the decoder by unwanted routes.

Figure 7: Easing the frame around the front of the decoder from above.

Figure 8: Easing the frame around the front of the decoder from inside the frame. Note the trimmed nub on the right.

Carefully trimming back the frames as shown in figures 7 and 8 removes this contact and everything works nicely. Note that the trim is above and below where the decoder will sit to clear components on both faces of the PCB.

Figure 9: Test fitting the decoder.

As you can see, there is a gap under the decoder at the back into which a speaker could fit, but I prefer an alternate location as shown later.

Adding LEDs and the motor connections

Next, head and tail-light LEDs are soldered to the undersides of the decoder. I think that the supplied LEDs are a bit too “golden yellow” for a modern locomotive so substituted “clear white” ones:

Figure 10: Supplied (left) and replacement (right) LEDs.

Figure 11: Head and tail-light LEDs fitted, AUX3 ,AUX4 and “blue” wires attached and motor feeds in place. The headlight is on but dimmed under “Rule 17”.

I have fitted green (AUX3), purple (AUX4) and blue (+ve supply) wires to the underside of the decoder in preparation for fitting separately controlled ditch lights later. I provided feeds from the decoder to the motor brushes by using strips of phosphor-bronze 1/16th of an inch wide and 5 thousands of an inch thick (1.6mm x 0.12mm) soldered to the appropriate pads on the decoder. These are pressed against the motor brush tabs by the body shell very much like the connections of the original lighting PCB. To prevent these from contacting the frame-halves, yellow “Kapton” tape has been wrapped around the frame rails under their path. In addition, I placed a strip of Kapton tape under the headlight and under the rear of the decoder to ensure that nothing touched the frame there. This is particularly important at the back as the solder joints attaching the purple, green and blue wires would otherwise rest on the frame.

And, of course, a speaker

My preferred location for the speaker is at the back of the frame. By trimming off the shaded area in figure 12, space is made for an 8mm x 12mm “sugar cube” type speaker (although I buy mobile phone spare parts on eBay rather than commercial “railway modelling” speakers).

Figure 12: The bit of the frame I remove to make room for a speaker.
A suitable baffle can be constructed from plastic sheet, purchased commercially or 3D printed (James does some). I attach the speaker baffle to the end of the frame with an adhesive “sticky dot as in figure 13.

Figure 13: The speaker installed.

The baffle provides most of the insulation needed to keep the speaker from contacting the frame but a short length of Kapton tape on the shelf underneath adds to the protection.

And that’s it, bar loading a suitable sound project and configuring the decoder:

Figure 14: A short video of the installation using the “Drive Hold” feature of the decoder to stop it moving while changing the throttle setting. Still got the ditch lights to do!

That is certainly easier than milling out the fuel tank to take a LokSound Micro V4 or LokSound Select Micro and also leaves the locomotive somewhat heavier as less metal is removed:
• With a Digitrax DN163K1C non sound decoder 116g
• With an ESU LokSound Select Direct Micro and speaker 114g
• With an ESU LokSound Micro V4 and speaker 105g
and weight equals tractive effort.

Figure 15: The same kind of frame with a pocket milled in the fuel tank to take a LokSound Micro V4 (or Select Micro), with channels through the back of the fuel tank, across the bottom of the frame and up the sides to get the wires to the lighting PCB to hook the decoder up.

Where next?

Next, the SD80MAC/SD9043MAC and the late-SD70M/SD709Ace.

I leave you this week by saying thanks to Chris for his post and I look forward to his how-tos on fitting LokSound Select Direct decoders into other locomotives.