Lokpilot 54650 slide in decoder

[RBrodzinsky]

Since the 54650 would definitely NOT fit into an Atlas GP38-2, I ended up simply using a LokPilot v4 Micro (this is for a companion unit to the GP38-2 I installed a 73100 in).  I created a couple of light/contact boards, and put the decoder under the rear board.

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I already have one person, who has seen this, asking me to make a bunch of these boards for his old Atlas units where he doesn't want to add sound.  The nice thing about these, it doesn't preclude sound in the future, and there are no frame modifications needed at this time.  I simply soldered the grey/orange wires directly to the motor tabs, and all metal in the area covered with Kapton.

[Steveruger45]

If I recall correctly, the 54650 looked like a no-go (which doesn't really matter as I forgot there is the 6-pin connection for a different non-sound LokPilot or other brand decoder) but I did successfully put a 73100 sound board in my FVM GP60M. However, it was not a drop-in fit. That said, I was able to get it to fit into the forward slots of the frame by loosening the frame halves a bit. The shell seems to be able to accommodate this fine and the trucks don't seem to want to fall out either, but they probably would if I went any looser. The board still wouldn't quite slide all the way forward into the (somewhat curved) front slots, as I guess the board itself is a tad thicker/taller, but it would slide in just enough for good contact and so the rear of the board would be (just barely) even with the back of the drive so the shell would clear. I did have to grind off a tiny bit of frame around the right-hand side, front slot as it got really close to a component on the top of the board that I was worried about potentially shorting, but that was it for frame mods. I also ran jumpers off the motor pads on the bottom of the board down to the motor tabs then applied Kapton tape between the pads on the bottom of the board and the frame. There were also a couple other pads at the edge of the board on both sides along the top near the middle of the board that sit really close to the frame that I wasn't sure what were, so I also covered these with tiny pieces of Kapton tape. They may be more frame contacts but they are not marked as such in the accompanying literature or in Peteski's findings, unless I  missed it. If I was to do any more frame grinding, I might increase the distance between these two pads and the frame a little. Finally, I placed a 9x16mm speaker, mounted diaphragm-out and facing up, in a scratch-built enclosure between the frame and the rear of the board. Even though the enclosure had to be kept pretty low-profile as you mentioned, the sound in this model is one of the best in my fleet....presumably because of the fairly large secondary enclosure area remaining inside the shell. I'll see if maybe I can grab some pics in the next day or two. Of course, your mileage may vary and attempt at own risk!

Thanks Russ.  Nice explanation.  BTW those additional pads you mentioned on the 73100 are indeed more left and right frame connection points.

[Steveruger45]

Since the 54650 would definitely NOT fit into an Atlas GP38-2, I ended up simply using a LokPilot v4 Micro (this is for a companion unit to the GP38-2 I installed a 73100 in).  I created a couple of light/contact boards, and put the decoder under the rear board.

(Attachment Link)

(Attachment Link)

I already have one person, who has seen this, asking me to make a bunch of these boards for his old Atlas units where he doesn't want to add sound.  The nice thing about these, it doesn't preclude sound in the future, and there are no frame modifications needed at this time.  I simply soldered the grey/orange wires directly to the motor tabs, and all metal in the area covered with Kapton.

Great idea Rick.  Now that the less than $20 54650 lokpilots have all gone and prices for these are now pretty similar to the hard wire lokpilot v4 micro this is an excellent way to go and avoid frame mods as you say.
I’m guessing pcb copper clad board around 0.6 -0.75mm would be suitable for most locos.  Of course that’s the thickness I don’t have right now.

[RBrodzinsky]

Note:  The two side pads on the 73100 at the narrowest portion of the board are motor contacts; not frame/track.

I am using 1/32" single sided copper board (digikey p/n 473-1008-ND).  That comes to 0.79mm.   I then add a 0.010" styrene shim (another 0.254mm), which brings total thickness to 1.05mm.  The Atlas frames are a bit variable, hence the shim.  If the frame gap is less than the shim depth, then the old-school buildup of solder at the contact pads is sufficient.

[tehachapifan]

Do we have a definitive answer on what the 4th 5th set of edge contacts are towards the center of the 73100 board (at the narrowest part of the board)? I'm not sure how to test it myself without risk of destroying the decoder. These contacts could easily be mistaken for more frame contacts, motor contacts, or...? Again, these are not labeled in the accompanying literature.

Also, I updated my previous reply to mention possibly having to remove a rear light tube assembly from the rear of the shell so the shell would seat down over the rear of the decoder. Can't remember at the moment which of my last couple installs I had to do this with (maybe both).

[RBrodzinsky]

Do we have a definitive answer on what the 4th set of edge contacts are towards the center of the 73100 board (at the narrowest part of the board)? I'm not sure how to test it myself without risk of destroying the decoder. These contacts could easily be mistaken for more frame contacts, motor contacts, or...? Again, these are not labeled in the accompanying literature.

Yes, see immediately above, these are motor contacts.  Real easy to test with ohm-meter, there is direct connection (0 ohm, no resistance) between them and their corresponding pads on the bottom.

[tehachapifan]

Thanks for the clarification, Rick. I did see your previous reply but also saw an earlier reply stating that they're more frame contacts, prompting further clarification/confirmation.

[Steveruger45]

Yes thanks.  Saved me blowing one up.