I'm trying to trouble shoot an inoperative smoke unit on my UP SD90 #628274-I think this is a late 90s engine.  I purchased it in 2009.

lionel does not have wiring schematics going back that far.

I found a previous post concerning AC voltage regulating and smoke unit. And it identifies what wires are what coming out of the voltage regulator. Does anybody know what voltages I should be seeing at those wires?  Specifically what voltage should be coming out of the regulator and going into the smoke unit. Does the smoke unit run on full track power?

i'm also trying to figure out what input voltages I should be seeing at the smoke unit itself.

any help would be appreciated



Original Post

If it's a late 90's engine, it doesn't have a smoke regulator.  I don't find that number, is it part of a set?

I suspect it's the 2007 LionMaster that came in set 6-30051.

That unit has an 8 ohm smoke resistor, and most certainly does NOT run on track power directly!  You will see a few volts across the smoke resistor with smoke on, the exact value will depend on the meter you're using as it's not a pure sine wave.

The smoke regulator has five leads.  Sometimes one of the black ground leads is missing, they're connected to the same place.

  • Brown: Serial Data from R2LC
  • Brown with black stripe: Smoke Element Power
  • Red: Track power
  • Black: (two leads), frame ground

Edit: correct wire colors, OOPS!

This is the engine and the set.  

Any idea what voltage value should be coming out of the brown wire?  Also, what value for the serial wire- Right now I think I'm getting about 7 bolts out of the serial wire and nothing out of the brown wire.

i do have full track power coming in on the red wire.

also, where does the brown wire go coming out of the voltage regulator?  What does it pass through to get to the smoke unit?

Like I said, it will vary based on what you are measuring it with.  I have a TMCC test board that I built to test the regulators, I have a light bulb across the smoke output to judge if the regulator is putting out voltage and also changing the output based on the smoke volume setting. 

I mis-spoke!  The brown wire is serial data, and the brown with black stripe is smoke unit voltage out.  I also corrected my original post to make sure nobody gets fooled with my mistake.

If you're reading 7 VAC on the brown with black stripe, you're getting smoke voltage out of the regulator.  The brown/black wire should go directly to the smoke unit, the track power should go through the smoke on/off switch.  I'm curious why you don't read anything on the serial data line, I get 3.4 VDC reading, and a 2.3 VAC reading on that line to frame ground.  If you read nothing on the brown wire, trace it out and make sure it's connected to serial data.


Photos (1)

Got it.  My brown/black wire does not go to my smoke unit.

I have three wires going into the smoke unit, two are black, one is red. The red wire is coming from somewhere on the main motherboard. One black wire is coming from the smoke on and off switch and the other black wire is coming from a pin on the main board.  All fairly thin gauge wire.

cjack posted:

Interesting tester. The 3 wires come from the radio board and track power? And the regulator attaches to the green terminals...?

Yep, the red, black, black/brown, and brown wires connect to the four pin header, it's labeled on the front.  The two pins are ground and smoke output so I can connect a test resistor in addition to my indicator light.  This is just a little section of my TMCC test board.  I keep adding stuff as I run across new stuff I want to test.  The other green terminals next to the speaker come from the R2LC smoke output for testing that under load.

PTA posted:

Got it.  My brown/black wire does not go to my smoke unit.

I have three wires going into the smoke unit, two are black, one is red. The red wire is coming from somewhere on the main motherboard. One black wire is coming from the smoke on and off switch and the other black wire is coming from a pin on the main board.  All fairly thin gauge wire.

That smoke unit only has three external connections.  What's connected to the other side of the smoke on/off switch?  That would have to be the black/brown wire if the regulator is going to supply power to the smoke unit.


Photos (1)

The other two going into the smoke unit. 

I have three wires coming into the smoke unit, two are black one is red. One black one goes to the smoke on off switch.  the other black comes from a pin on the motherboard and the red one comes from a pin on the motherboard. 

if the brown wire passes through the smoke on/off switch, (assuming that is power to heat the element and run the fan,) what do the other two wires do? 

My brown wire has about 7 V -assume that's the serial wire. My brown wire with a black stripe is showing no power coming out of it. I'm assuming at this point that my AC regulator is not workin as I do have power at the red wire going into it And I have continuity on both of the black wires to track common.

The brown wire should NOT have 7V on it.  The brown/black should have about that, maybe a little less.  The serial data should never have more than 5V on it.  The serial data does NOT go through the smoke unit.

At this point, I suggest you take this to someone that can untangle what is going on.  Something is quite wrong.

Normally power for smoke unit comes from MB to switch and from switch to Smoke unit.  Lionel had a few wiring conventions, and also a few types of smoke units.  Do you have electronic components and chips on smoke unit or just diode, cap and VR?  Lionel also had a few where the fan power was interrupted with chuff switch, but not on a diesel.

You need to trace to source.  Many MB have silk screen id on connectors to see what it is.  If not trace back to R2LC pinout.  If you learn the TMCC arch, you can understand what they were doing.   Also some units had double ground to smoke unit, others did not. They had a solder bridge/trace on the connector PCB of the smoke unit.  Pictures would help tremendously.  G

MTH Authorized Service Center

Authorized ERR Dealer

Lionel Independent Repair Tech

Virginia Train Collectors Member


All wiring is in its original configuration as I have not removed anything the engine was brand new when I bought it.

One of the reasons why I was looking for a wiring schematic is because lionel connected wires of different colors together and then routed them underneath the motherboard which were very hard to trace. (See the picture )I have not moved or messed with any of the wiring just trying to trace voltage.

As you can see from the picture, the brown wire with the black stripe becomes black- (it's soildered to a black wire) where it eventually runs to the on and off switch for the smoke unit. I had to do more disassembly to find that connection and color change as the wires were tucked underneath the motherboard. This is how the engine came from Lionell. I'm really surprised that they change colors of wires. Makes things very confusing.


Photos (3)

Your remarks above are confusing.  I see 2  wires into the 3 pin connector on smoke.  Should be AC in.  The 2 pin routes 5V made on the smoke unit PCB to the smoke motor.  Should have diode, cap, and small 5V reg on underneath of PCB.  If there is a 3rd black wire coming in to the smoke unit it may be to independently control smoke unit 5V components.  Se my remarks above.

As far as wiring the AC reg, john gave you the pin/wire info.  But Lionel wired these many different ways.  So you might have to lift the MB to follow the wiring.

This is why I hate working on Lionel, especially now that diagrams seem to be leaving the old tech search function.

First you could unplug the 3 pin on smoke, plug one in with AC wires available to independently test smoke unit.  Does it work, including fan.  Go from there.  Does switch work, swap r2lc, then swap ac reg.

Or, use meter and find out how it is wired checking pin to pin.

If this was conventional TMCC no AC reg, the smoke out of the R2LC would go to switch for conventional and tmcc on/off control.  IE if switch off smoke does not work either mode.  From switch to smoke unit power in.  Now if the AC reg is inserted, it could go between switch and smoke unit, with serial data also coming from R2LC.  G

MTH Authorized Service Center

Authorized ERR Dealer

Lionel Independent Repair Tech

Virginia Train Collectors Member

Thanks for the response. I understand that the pictures can be difficult sometimes to see the small wires but there are three wires going into the smoke unit, two black and one red That are part of the three pin connector.

over the weekend I installed an AC regulator and new smoke unit that I ordered from my Lionel. I now have heat to the element but the fan is not coming on. I also have no control over the smoke smoke unit using my TMCC remote.The element comes on immediately with track power and will not turn off to using the TMCC remote.

I tested the fan motor independently by applying voltage directly to the contacts and the fan motor does work

I also tried reprogramming the engine using  procedures I found online. Reprogramming has not done anything for it. 


Add Reply

OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653