UP F3 Smoke units

What do you mean "the smoke units work"?  Since those have an on-board fan power supply, if the heater is getting hot, the fan should be getting power.  Given that fact, replacing the smoke unit certainly should have corrected any power supply issue on the smoke unit.

Now, these do have a smoke voltage regulator that is a common trouble spot, but that failing would also prevent the smoke heaters from getting hot.

So, what are the real symptoms, because I can't see any way your description fits the possibilities.

I know this doesn't sound correct but the smoke resistor does heat up but I just get a little smoke from the unit because the fan doesn't come on to push the smoke up. I've been having Mike Reagan who worked at Lionel Service work on my locomotives back in North Carolina and I talked to him about the problem and he asked me what the voltage in a board was but I'm not sure what he is talking about. I was trying to fix the problem myself so I wouldn't have to ship the to him for repair. What is confusing to me is why does the element heat but the fan won't work. Thanks for you help gunrunnerjohn I appreciate you help.

I can only guess that the fan isn't getting enough voltage on the input for the regulator to work.  As you say, replacing the smoke unit doesn't change things.

Try this.  If you have a source of around 7 VAC (not any more), connect that to the old smoke unit power input terminals.  If the fan spins and the smoke element heats, it almost got to be the voltage regulator module.

Funny thing you should mention Mike, his suggested fix is to put a 27 ohm resistor in the smoke unit and wire it directly to the R2LC smoke output eliminating the fan.

Thanks for your advice John I will try that. Do you happen to have any paperwork that shows how to wire it to the R2LC board. I know it's not a big deal about the smoke units working or not but I'm old school and I like my locomotives to work like they came from the factory. I also wanted to ask you do you have any idea where I can get a 6208225186 side frame for a Lionel UP SD-40 T2 wouldn't you know one of the tabs broke off the one on it so it came all the way off and I've looked everywhere for one. I even asked Mike and he couldn't help me. Thanks again for your help. Gary

I have no idea about the sideframe, I'd probably break out the JB-Weld if I had that problem.

I don't know about the specific wiring for that particular locomotive, this the kind of thing that is a lot of "seat of the pants" stuff when you see it.  It's simple in concept, and most likely simple in execution.  Basically, you need to trace the wire from pins 5-6 of the R2LC to whatever motherboard pin they come out on.  Those go through the smoke switch and on to the smoke unit with the new 27 ohm resistor.  If, for some reason, the smoke pins were not brought out to a motherboard connection, you can solder to the back side of the motherboard on pins 5-6 and route that to the smoke switch and to the smoke unit.