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Hi, I'm new at this, so please correct me if I make a mistake.

I have a JLC Big Boy (6-11126), smoke unit has failed, the fan still works, and I have track power (whatever I make it) at the plug on the board, but no power at the smoke resister, being I have power to the board and the fan still works I'm assuming the board is bad that you can't buy. any help would be appreciated.

Original Post

The smoke unit in question is a 6 Ohm model that Lionel stopped using several years ago - it was a prolific smoker used in early Legacy engines like the FEF-3 and GS-4 but prone to blow the AC regulator. Lionel later recommended substituting an 8 Ohm resistor. I recall that for some length of time after that, a replacement PCB as opposed to the entire smoke unit assembly was available but unfortunately I no longer see that in Lionel's replacement parts pages.

I am not sure that there is any engine-specific logic on the PCB that would prevent substituting another smoke unit if you have to - hopefully someone more expert can opine on that. However, I have worked on a number of these and the PCB itself seldom fails but a component on it may have gone. I can't guess which one it might be because don't quite follow where you are measuring the power to the board and resistor and getting a track voltage reading. I suppose it's possible that only the resistor has gone and you might want to open the unit up to have a look at it. 

First off, that's a dumb board, so there's nothing to prevent you from replacing it, no logic on the board.  However, unless the board is burnt badly, you can simply replace the resistor with an 8 ohm one and then fix whatever is preventing the resistor from getting power.  Replacing the smoke unit will be a lot more work than fixing a simple problem with the one you have.

Some close-up pictures of both sides of the smoke PCB would help us help you, I don't have one of that particular model to look at.

Thanks for all your replies, I'll try to take them in order.

BRUK, I checked all the plugs and wires, everything looked good. 

HANCOCK 52, If I can get the pictures up there is one of just the male plug that I disconnected then connected to the red and black wires of that plug, when track power was on (whatever voltage) it was constant, I think it was AC voltage. Although the resistor looks bad it still measured 6 Ohms.

GUNRUNNERJOHN (like the name), I hope I can get the pictures up for you, it's such a nice engine I would really like it to smoke.

Thanks again.




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I don't see any physical damage to the PCB, and since the fan works, there's nothing on the PCB to prevent the smoke resistor from heating.  I can see the traces from the GND & HTR pins and they're fine.

Let's start with the basics, measure the resistance of the smoke resistor and tell us what you get.  With this unit, I'd put the 8 ohm resistor in, and also you have to make SURE those screws/nuts are tight, that's a frequent cause if issues.  another thing, make sure when you reassemble it that the smoke resistor does not touch the sides of the smoke chamber.

You don't need a new smoke unit.

The only connector I checked was the 4 pin that goes to the PCB, I only checked the red and black wires, that's where I get whatever voltage I put in up to 20 volts (red goes to on, off smoke switch, of coarse black to ground one white wire goes to a cherry switch and the other white wire goes to the AC regulator).

Well I have that AC regulator #691ACRG103, I purchased everything I could for that engine, I hope it's not to bad to put in, I'm 71 yrs. young and I have essential tremors, (the shakes) makes it very hard for me to solder.

Correct, track power, ground, smoke element voltage, and serial data come to the smoke unit.  You're missing smoke element voltage.

Installing the regulator is usually accomplished by clipping the wires near the old one.  Then you can splice the wires together, much easier than soldering PCB pads.  There are typically two black wires (both ground), but sometimes only one is used.

  • Black (frame ground)
  • Red (Track power)
  • Brown (R2LC serial data)
  • Black with brown stripe (smoke element power)


Click on graphic to expand.  This graphic is close, but the newer smoke units got the chuff from the serial data, thus the chuff switch isn't connected to your smoke unit.

Lionel Smart Smoke Unit Wiring [Steam)


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  • Lionel Smart Smoke Unit Wiring (Steam)

Sorry, this is later than the other posts above so has been overtaken by them but I include it for completeness.

Fortunately those AC regulator modules are still available from Lionel (and now I note that you have one already).

This is unscientific and I don’t want to confuse the issue, but I recall a thread  a couple of years back where we were discussing this generation of Lionel smoke units and this PCB was mentioned, which is still available from Lionel but you have to search under replacement part number (not product number) for 691SSMUK02:


The part number printed on the part, which I have got from Lionel in the past and used on one of these units, matches your photo above. But replacing the PCB won’t restore operation if it’s the AC regulator that has gone. 


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Last edited by Hancock52

Well John I think your on the right track with the AC regulator, the old one had 4 wires and was grounded on the frame with a screw, see picture, the regulator was a little loose, you can see burn marks on the screw hole, also the replacement regulator has 5 wires, (see picture) two of the blacks look the same, is it going to matter which black goes to frame and which goes to existing black on old regulator. thanks for the graphic I'll print that out, and maybe pick up that board if it's still available.P1140006P1140003P1140002 


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gunrunnerjohn posted:

IMPORTANT!  The regulator triac MUST have the isolation from the chassis, if the plastic sholder washer and insulating pad is missing, you'll cook the new one!

The last one of these I got did not look like the Lionel replacement parts page image copied above. In particular, all the components were within the black shrink wrapping (no triac sticking up outside of it) and there were five wires instead of the four on the original part. The part I got looks exactly like the OP's replacement part and is really fairly small. 

I still put some insulation between the shrink wrap and the frame and connected the four original wires leading to the old regulator to what I worked out were the corresponding outputs on the new one. I can't now remember exactly how I dealt with the fifth wire but GRJ's diagram above looks familiar. Anyway, it worked.

Well thanks guys, this is a big help, it looks to me like the two black wires both go to ground, that being the case, I'll run one to the original black from the old regulator and one to frame ground, don't know what else to do there.

John, I know what you mean, I once missed an isolation pad on a board for another engine "poof" learned the hard way.

Thanks again, this is going to be awhile, but I'll definitely let you the outcome. 

Yes, as I said, there are two grounds.  Only four wires are needed, I think the two grounds were there to make wiring easier.

Most of the TMCC ones are as Hancock52 states, totally shrink-wrapped.  However, later TMCC and early Legacy started bolting the triac to the chassis to aid with heat dissipation to try to slow down the excessive failure rate of this module.  Not sure how successful they were, but that's the rational for exposing the triac.

FWIW, the metallic side of the triac normally faces down on the chassis on top of the insulating pad, then the insulating bushing goes through the hole to insulate the screw from the metal base and into a threaded hole.

I have the new AC reg. wired in, it does smoke,      "a little"    I'm using Legacy control, the off, low, med, high, does not matter what setting I use I get the same results, a little smoke at very low speed, anything faster you don't even see it,  NOW, if I keep pressing for more smoke (med and high) as fast as I can it will fill the room with smoke, but as soon as I stop pressing the button it goes back to a little smoke, pressing and holding the button down does nothing. Any ideas?

Make SURE the four wires are connected in the proper places.  I suspect they are, if you connected the smoke (brown/black) to the serial data, things would be a lot worse!   That was a bad choice of colors by Lionel, don't know what they were thinking.  Having two wires that look brown is pretty dangerous, swapping them and nasty things happen all over the place!

If you just matched all the wires up, being careful with the two brown ones, not much else to say.  That's all there is to installing the regulator, other than bolting it down with the correct insulating hardware.

To the OP, you can't go wrong listening to the fellas on the forum; they helped me thru rebuilding the main smoke unit on my Big Boy; got all my parts from Lionel but I replaced all of them - resistors, PCB, fans, reservoir, wadding - cost a bunch but unit now works great and I know how to rebuild a unit - no worries.  For some tips maybe you can look at my trip:

Based on my own experience of these units, and what you report about what you have seen, a tune-up of the unit itself is certainly worth doing, as well as checking simple potential faults like the alignment of the stack and whether there is any fluid or wadding blocking the output funnel. These smoke units came stock with the pre-cut pads that Lionel no longer sells as replacement parts and the resistor was installed well down into the wadding material but with no blockage of the channel between the fan housing and the smoke chamber. With a 6 Ohm resistor mine smoked like nothing I have ever seen. When I eventually had to replace the wadding with ordinary rope wadding shredded and packed into the chamber, the smoke output went down somewhat but was still copious by Legacy standards. In one of my engines, I did not replace the 6 Ohm unit with an 8 Ohm unit but I have seen it done and the smoke output was not greatly affected - at least where the unit was otherwise correctly packed and had been fully charged with smoke fluid.

However, I can't help thinking that there might be something else that needs adjusting and in particular if you are only seeing a marginal difference between the original and replaced AC regulator. Have you tried an engine reset? This is an RS5.5 engine so it seems it has the early modular boards and I wonder if something has gone wrong with the settings.  I don't know how to diagnose these other than by trying a reset; someone more expert might have an idea. I guess you have to discount the possibility of a component on the PCB going bad if you are getting power to the heater. Have you measured what it is at the resistor terminals?

In terms of wiring up the AC regulator, I can't second guess what GRJ has said although I am racking my brain to remember what I did with the second ground wire. I might have tied it in to the other ground wire (see the diagram posted above) or simply cut it off as surplus to requirements. I do remember puzzling over this but I can't trace any thread in which I asked for advice on the forum. 

Last edited by Hancock52

I don't think that this will add anything new but I post it for the sake of completeness.

The guidance I got on replacing the AC regulator came from Mike Reagan himself and was given back in 2011. He said:

"The AC Reg consists of 4-5 wires that need to be cut and spliced and soldered and covered with shrink tubing. The wire designations are on the PVCB, under the heat shrink wrapper. The board must be screwed to the frame and electrically isolated from the frame too."

I partly cut away the wrapper to see the wire designations and then sealed it up again. The regulator I got back then did not have the triac outside the wrapper any more than the ones I got later. 

Some of them are totally encased in the heatshrink, others have the triac hanging out to be bolted down for heat-sinking.  I have new ones in both configurations in my parts boxes.  Most of the Legacy ones went with the exposed triac, probably because they failed so often without heatsinking.

As for having to open it up, I just match the spacing of the wires to the standard pinout, I've never seen one that has a different layout.


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  • mceclip0

Hi people, thanks for all the replies, I did put in a new resistor with new wadding material, I think it's OK, if I keep pressing the increase smoke button I can fill the room with smoke, soon as I stop repeatedly pressing the smoke button it goes back to almost nothing, YA, I did have very very little smoke with the old regulator makes me wonder, but I can't figure it out, I used the ground wire (on the 5 wire regulator)  that seem to match the ground on the old (4 wire regulator) left the second ground detached, then just for kicks I grounded the second ground wire to the frame made no difference, had to try.

I thought the 4 ohm would be pushing my luck, but I had to ask.

Well I guess a little smoke is better than nothing, which is what I started with, and if I want to keep pushing the increase button I can have a lot of smoke.

Thanks again.

I've never had that issue. And if GRJ says it's likely an AC Regulator problem I defer to him. But I still wonder if it could be a software/control board issue as what you describe sounds like defaulting to the low smoke setting after you ramp up the smoke via the remote.

That prompts me to ask if you are using a CAB2 for control, which version of Legacy you are running and what settings you are using for this engine? I have noticed a couple of odd things about the latest version of Legacy when running some TMCC/ERR engines in that the commands don't execute exactly as they did under older versions. That really should not happen with a Lionel RS5.5 engine like yours.

Reprogramming is not just for TMCC.  Did you follow the manual instructions to reset the locomotive?

Sadly, when I've seen the smoke regulator forget the smoke settings, it's usually a bad regulator.  I have seen the same symptoms, and it's always been a regulator replacement required.  FWIW, the smoke heater on this model isn't affected by the R4LC as the smoke output of the R4LC isn't used, or is used for the cab light.

My Legacy system has been at the latest version since it came out, I've never had it cause this kind of issue with any locomotive.


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  • mceclip0

Those all seem to be correct settings; I don’t see anything in the Legacy v 1.6 manual that indicates any special/different settings for this engine. There is an option to enter the RS settings as RS5 but your manual describes this as a Legacy Railsounds engine. This is a JLC engine; I don’t have it but the couple of JLC engines I do did not come with an orange module and there’s no reference to one in your manual. Unless there’s some quirk about RS5.5, I can’t see that the settings are incorrect.

Process of elimination: have you tried starting it up in conventional and seeing if the smoke volume is greater at higher voltages?

I notice that there is a wiring diagram for this engine, copied below:


It may make no difference but this (top left) shows (1) the AC Reg. second ground connection not used/clipped off and (2) the AC Reg. model as 691-ACRG-100. That model is listed as obsolete and unavailable at Lionel, with no specific alternative listed. There was another model, which I think is also designated obsolete, 691-ACRG-101, still available at Lionel but the alternative to that is the one you and I both have listed as -103 (S03 Code). That did work with my version of this particular smoke unit.

At this point, I wonder if the answer is buried in Lionel’s own knowledge base. Mike Reagan occasionally posts here and a shout out to him @Mikado might shed some light on this. I believe he is still doing great repair work.


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JGR, I reprogrammed this engine to the letter as per your post, there was no difference. In conventional mode I saw nothing, but full speed is to fast on my layout, I tried CAB 1, different RS, and pressing the + button in any of those modes does not give me more smoke, I have a second Legacy controller I tried, no difference there. I'm thinking of getting another regulator to try, a spare would not hurt anyway. thanks for the wiring diagram I'll hang on to that, I'll contact Mike to see if he wants to contribute to this problem.


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