ESU LokSound Micro Select Direct install in Atlas GP38-2

I have successfully installed one of the new ESU LokSound Micro Select Direct decoders (73100) into an Atlas GP38-2. This was a fairly easy but interesting install, due to the minimal amount of space available in the unit.

First off - the video. Since this is not my loco, I left the hand-rail protective foam in place (which does mar the look of the video a bit)



Here, you can see the LokSound 73100 board, as compared to the stock NCE board. The NCE board was not functioning well (needed >30% throttle to move, then minimal speed control, and no response from decoder even on programming track). You can see that the 73100 is a bit shorter, and narrower in spots from the original board




Here is the board in the chassis. It looks like everything fits well, in the first photo, but on closer inspection, one can see that only the two front tabs are actually contacting the frame, and loosely. The contacts for the rear position are inset a bit, and do not touch. To ensure a snug fit and good contact, I ended up putting small blobs of solder on the front two pads, which now make excellent contact and hold nicely

 

The real fun came in figuring out how to cram a speaker and enclosure into this little beast. This photo shows the rear of the board and the overhang over the frame


It isn't much space, compared to my "go to" Shapeways enclosure for the Soberton 8x12mm speaker


So, I milled down the right side of the frame to match the left, and enlarged the lowered edge just a bit


But even with that, and sanding down the bottom of the enclosure as far as possible, there was just not sufficient space. The top of the speaker would still be just at the bottom of the components (not a good thing). So it was time for a custom enclosure. I designed it to fit in the space under the board, and use the ledge over the flywheel to give me back some of the volume lost from shortening it. After using thin styrene cement, and CA to attach the speaker, I also sealed all joints with Bondic, to ensure the enclosure was airtight.

 

Here is a side view of the speaker enclosure


And, sitting in the frame (before I squared off the excess Bondic)


It turns out that, for this model, the two little board mounted LEDs (Aux1 and Aux2) actually provide sufficient light and are positioned well for the front and rear headlamps, so here is the fully assembled unit




I have not installed any added capacitors, and in playing around on my programming / test setup, had only one minor interrupt, on speed step 1/128, so I moved the Vstart to "2" from "1", and no further issues.

To help wedge the board in place, I put a 0.010" piece of styrene between the board and chassis in front, and a 0.020" piece in back, which also helped provide a bit more speaker/board separation.

 

Umm, at the very top of the first post

 

After discussion with Jeff, I went ahead and added 3 20V 220uF poly-Ta caps for 660uF of keep alive protection.

These are AVX caps from Mouser, p/n 581-TCN4227M020R0100

There are two caps, stacked, in the "lightbox", and 1 cap sitting on the porch below the decoder

 

On the +UB pad, next to the Aux3 and Aux4 pads on the bottom side of board

 

Yes, since the caps on the board are directly connected to the decoder negative (ground) as well. The on-board capacitors have their negative sides facing outwards. There is a thread over on The RailWire where a member did a full analysis of the three new Select Micro Direct boards, highlighting all the components and where it is safe to make connections. There is no clean solder pad provided that is the board ground.

 

There is no exposed ground on this board, anywhere, except for the board mounted capacitors.

 

Ignore it. By using the 2nd set of contacts at the front, and shimming them so that they are in firm, that is sufficient to power the board. The different contacts are at different widths specifically to accommodate different frames