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I am a "value shopper" and was looking for a scale proportion F-Unit.  The current Atlas Locos look great, but are out of my price range.  While I have been buying a lot of Weaver Items, I had an experience with one of their "chain drive units", and was not impressed.  As a retired Mechanical Design Engineer that is as polite as I can be about that design.  Because of this I also know just enough to be dangerous when it comes to Electronic Circuits as you will see from my questions below.  I come from HO, so all of this seems very complicated.

So I purchased a K-Line F7A Unit by itself.  It has no box, accessories or DIRECTIONS.  From reading prior post, it is the 3rd gen, has mirrors and smoke unit.  It has a male tether (pins) hanging out the back.  It appears that this was part of a 3 unit set.  The F7B was unpowered, had a male tether on one end, female on the other.  The other F7A which was already sold had a female tether.  I have hooked up power and this unit does NOT run independently, so must be trailing unit.  I think it is beautiful (SP Black Widow), so want to make it work.

I had posted last week in wrong forum, GunRunnerJohn and Norton had responded, but couldn't see all your replies, I want to thank you.  I did find out from the seller I could return if it wouldn't run, so didn't cancel order.

I am including some pictures of the Loco.  I am no expert on this, so need some advice.  If I had instructions or better yet a schematic, it would help greatly, does someone have one they can post, or E-mail me?  I hooked regulated DC to the unplugged harness to test the motors/drive and they work great.  Same with Smoke Unit fan motor.  The board obviously has the a rectifier to convert the AC (4 Power Diodes).  Not sure if it has the ERU, do the components next to the Power diodes, left of center on the board, perform that function?  Also noticed that it has a speed sensor on the forward motor, is this used for speed matching the two motors or only comes into play when MUed to the other unit?  Or is this for the Cruise Control?  So if I want to operate Independently "conventional", can I just rewire to get power directly to the board?  If so where on the board does the AC Input go.  Would all the lights function correctly?   Any help would be most appreciated.

Also dislike the front appearance, believe that it might have originally come with an optional closed or dummy coupler, fixed pilot.  Any idea where I could obtain one?  Looks like moving the electrocoupler to the rear truck should be fairly easy.  Thank you!

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@MainLine Steam,

You're actually lucky with this.

Many folks who have the A-A K-Line sets in this second generation (in Yellow/Black Boxes) are trying to upgrade their controls and face a quite a bit of work as a result.  The A-A's as a set have 4 motors, which is more than most upgrade electronics can handle.

Since you only have one, i.e. two motors instead of four, you shouldn't have as big a problem.

Start with this link.  It describes what the upgrade consists of, ERR Cruise Commander, which you'll need, and modifications to it to handle four motors, which you won't:

    How To: ERR Cruise Commander With Tethered Bridge for 4-Motor Operation | gunrunnerjohn

You'll learn a lot about the K-Line A-A sets and hopefully enough to guide you on your single A upgrade.


Last edited by Mellow Hudson Mike

Hi Pete - Yes the unit does have a cruise switch, the lead is unplugged in the pictures.  Did that so I could get at the 4 conductor square plug easier.  So this was set-up for a radio receiver?  Can it be run off of standard regulated AC?  I am still trying to learn all this 3 rail stuff.  HO 2 rail DC is MUCH simpler.  If you want digital control, after a slug-fest in the early days (1980's and 1990's) a NMRA standard (DCC) was established and that was that.

@Norton posted:

The picture shows a K-Line Cruise board. This is the lead engine but what appears to be missing is the R2LC and its motherboard. No telling if that board works without getting a radio board to drive it. It may be easier to just replace it with an ERR Cruise Commander.

Actually, some of these sets actually had a cruise board in both ends, but the one he has is the slave and never had an R2LC. I just finished a repair on one of these, it had a bad cruise board in the master, so we did a CC-M and a tethered bridge so I could run all four motors from it.

This is NOT the lead engine.  You could wire up a simple motherboard and an R2LC if you assume the K-Line cruise board is good, but that's not always a good assumption.

OK, I was wrong. Its been many years since I have had my F7s opened up. Yours is in fact the trailing unit. Unlike most K-Line multi unit engines, these have a motor driver in each powered unit but use a single Radio board to drive both units. The lead unit with the radio board also has the Railsounds boards.

At this point its probably better to just get a ERR Cruise Commander and Railsounds board to replace the K-Line board in there now. At least you will have a manual on how to wire it. If you try and just get a radio board and motherboard you will have to figure out how to wire them together yourself.

Other options are just get a reversing board and run the engine with a transformer.

Unlike DCC there are dozens of ways three rail engines are powered. Lionel has maybe 7-8, MTH 3, plus Electric Railroad, Train America Studios, and Digital Dynamics.


I see John posted while I was typing.

Last edited by Norton

You guys are making me feel less like an idiot!  Thank you!

Being an Engineer I always want to know how it works, it's a curse.  LOL  So with the board I have does it contain an ERU?  Is there information somewhere of what this board actually does?  Can it by direct wired to rail power and perform like a QSI DCRU?  I am new to this and this is my first Diesel Loco purchase.  Prior Locos have all been Weaver and Williams Brass Steam (QSI DCRU).  I had figured out how those boards work.  More comfortable with 30 year old electronic technology.  I still haven't bought any items for a layout yet, just accumulating Trains at this point.  I have have toyed with the idea of gutting the boards and running 3 rail DC but then lose directional, constant lighting features.  Plus not sure about life of smoke units on DC.  I have been testing purchases with my MRC HO transformer.  The AC output on it is constant 18 volts, so don't run things very long.  When it didn't work on this K-Line Loco I traced wires and used the variable DC output to test the motors.  I have accumulated quite a few K-Line aluminum passenger cars and the "streamlighting" is set-up for AC.  Plus when more daughter needs to unload this stuff probably better if it is AC.

When you plug the 4 pin black connector back in that board it will be connected to track power. If you have a AC transformer see if it runs at all and if it reverses. That board is unique to a few K-Line engines. Not many have documentation on how it works and I know I have not tried running mine without it being connected to a radio board, aka R2LC in Lionel speak. Try it, as you have nothing to loose.


Last edited by Norton

Hi Pete - Before I opened up the engine I tried it with AC, although now that I think about it may not have cycled through, so possible it was in neutral, although didn't see lights come on.  There is no lock-out switch on the engine just smoke unit and cruise control.  I will try it again tomorrow.   Thanks again for all your help.  BTW I sent you an E-mail earlier tonight when I saw your message to PM you.  I am just a basic member so don't believe I can do that.

Plugged everything back together.  With 18VAC applied to the truck, the only thing that worked was, cab light came on.  The position of both smoke unit switch and cruise switch had no effect, tried all 4 combos.

I'm thinking if I had a pin out diagram for the harness, I could test everything, if I knew how to jumper.  With 10 pins, I am not going to attempt without a diagram, as doing that I could definitely damage things.

No point in doing testing. It really needs a R2LC to work and an R2LC needs a mother board to connect to the K-Line boards, sound, and smoke unit. You can get the boards from Lionel and maybe come up with a solution but it would be an order of magnitude easier if you had the leading A unit that went with your engine, even if only for testing purposes.


The smoke unit has a control from the lead unit, there's a triac that is controlled by a signal from the lead unit for the smoke operation.

As Pete suggested, I think the way to get this running is to use the ERR Cruise Commander and the ERR RailSounds Commander.  Cobbling something together to use the K-Line cruise is not that good an idea, they don't have the reputation for longevity, and we don't even know if it's alive now.


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  • mceclip0

Hi John - I was typing the above, did not see your reply.  See now that "you're the man" for electronic controls for three rail.  So based on knowing this board needs to be fed serial data, there is no "cheating" this board to work directly off conventional track fed AC.

Is there some comprehensive source that explains all the different variations of 3R boards that have been used?  As stated earlier being a retired Mechanical Engineer I have an insatiable quest for knowledge about how things work.

BTW do you have a junk pile of QSI DCRU boards, or something similar, gutted from Locos you have upgraded?  I intend to build my layout around conventional 0-18VAC unless some can convince me otherwise.  For an old man like me, staying on the throttle is safer (and less stressful) then trying to keep track of what I am doing with a controller.  LOL  I really don't want a head on collision between 2 of my brass steam locos.  Thank you for your help teaching me what is what - Jim

Well, there are plenty of 3-rail electronics guys here, I'm just one of the pack.

As for the K-Line Cruise board, there is no way I know to "cheat" it and make it function stand-alone.  That being said, there is a conventional version of the K-Line Cruise board that does run stand-alone.  It also looks exactly like the command version, but I'm assuming it has different firmware.  Since we don't have the firmware, and no way to get it, it's not possible to make the command version into the conventional version.  I actually have the tools to load firmware on those boards, but no source for the actual code.

As for a comprehensive source of 3-rail electronics types, don't you just wish such a thing existed!   In our dreams it would also include complete schematics for each type.   Well... no, such a source doesn't exist.

I see conventional boards coming around all the time, and from time to time I have sold of excess boards that I have from command upgrades.

As for conventional vs command, both are certainly viable ways to run your RR.  I personally like the command environment, and the ability to run multiple trains on one track, the pinpoint control, and the great sounds keep me in the command camp.

Thanks Pete and John for all your help, just saw your latest replies.

Oh and I should have said above that if I was to go a high tech route for train control, I would use a computer as a CTC control / display for a block system.  Guys were doing this in the 1980's in HO before the manufacturers got into the onboard controllers.  Since this is how real railroads do it, if good enough for them, it works for me.  Although maybe a system of "Virtual Blocks" could be set-up via GPS.  Train detection would be the redundancy.  For the model world probably just have to stick with train detection.   

Is it possible for the OP to add an R2LC and a small motherboard?  What connections would he need?

Track power Pins 1,2,3,4

Rear light Pins 9,10

Antenna Pin 23

Forward and reverse PWM to Motor driver Pins 16, 18

Most of these connections would be in the existing tether but I suppose the challenge is figuring out the pinouts.  I have yet to see any K-line board diagrams online.


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