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I have three different AD-20 modules here, and I'm trying to identify the functions.  All the actual PCB boards are the same, obviously the function is determined by the uP on the board.

The one on the bottom with the red dot on the uP is the diesel ditch light AD-20, the one in the middle with the white dot on the uP is the wireless tether AD-20 that supports the tender coupler, reverse light, and serial data repeater.

The burning question is, what is the function of the one with the green dot?  It doesn't appear to do much in response to serial data, and there are no outputs for anything I've been able to determine.  The two outputs that drive lights a couplers don't react to anything I send over the serial data.  Since I have three of them that all react the same, I am concluding they're probably not all defective.

Anyone got a clue what the function of that particular code base is?

Lionel AD-20x Types


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  • Lionel AD-20x Types
Last edited by gunrunnerjohn
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I checked my stash of the non-modular AD20 boards and didn't see any with a green dot. I'm also not aware of another use besides the 691-PCB1-012 with the red dot for a diesel's ditch lights, and the 610-8056-200 with the white dot for the wireless tether and back-up light/coupler.

These non-modular boards were only in use for a limited time -- basically around late 1997 -- before changing to the modular form of the board in 1998.

There is another part number associated with these boards, 610-8232-110, but it references back to the 691-PCB1-012. The 6-18232 Soo Line SD-60 may be the only diesel to use non-modular board, the 610-8232-110 and/or the 691-PCB1-012.

And the two Hudsons from late 1997, the 6-18056 NYC with the Vanderbilt Tender and the 6-18062 Santa Fe Warhorse, were I think the only two that used the non-modular AD20 steam board.

Lastly, I've had a heck of a time getting working non-modular steam AD20 boards from Lionel. Not sure if they were defective or just never programmed (although they did have a white dot) but they were completely DOA, just like your green dot boards.

Sorry I can't help further, but would love an update if you learn the answer.


I'll keep looking, I was surprised there was a green dot one that doesn't seem to do anything.  The fact that I actually have three of them that all do the same nothing seems to indicate I'm probably not looking in the right place for their function.  I just don't see any activity regardless of what serial commands come in.

I am only aware of the two functions for these boards, the ditch lights for diesels and the tender IR link and light/coupler function for steam.

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