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Hi all,

I have the 6-34635 Legacy F3 A-A set in the SF Cat Whiskers. This post is concerning a smoke issue with the 6-35637 non-powered A unit in the set. I run them only in Legacy with a CAB-1L.

The unit responds normally to all commands except the Aux1 -8 or -9 command that controls Smoke off or on. The electro coupler fires and the DIR switches changes the lighting just fine. But it takes multiple tries pressing AUX1 and then 8 or 9 (as appropriate) to turn the smoke on or off via command. I’d say maybe on average 6 or 7 attempts before it triggers the desired response.

I thought it might be the CAB1L, but any other units on the track respond correctly and immediately. It’s just this one unit and only the smoke commands that are a problem.

I could probably live with this since I rarely run with smoke (especially these, they make a LOT of smoke!) but I’m one of those guys who likes things to work as designed.

Any thoughts on the root cause and the complexity of fixing?

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I agree with John, and have experienced the same symptoms you have described.

A word of caution. Sometimes the regulators just quit, and smoke ceases for good.Other times they can go out in a blaze of glory.

This will produce a ridiculous amount of smoke for a brief period and creating heat that could risk damaging a plastic shell.

I've only experienced this on a die cast steamer so there was no damage to the loco. Some have even reported seeing the resistor glowing in the stack.

It might be advisable to shut off the smoke with the switch on the loco until you replace the regulator.

Last edited by RickO

I've seen a couple of meltdowns in person, and repaired a few more.  It is spectacular smoke for about 20-30 seconds before the smoke unit resistor and PCB burn up.  The stink of burned PCB lasts for years!  Both of my in person experiences were with diecast steam, so no shell melting.  In a diesel if that happens it will melt the shell if you're not quick on the power switch.  In command mode the normal 6-7 watts in the smoke unit ends up being 45-50 watts when the regulator shorts, that gets pretty exciting!

Thanks all! As usual you all came through with the answer right away. Armed with your comments above I did a forum search on legacy smoke regulators and now I see that these smoke units are a problem.

It seems to me that the smart thing to do would be to get the smoke regulator replaced on this unit, but while at it have the shop change the 6 ohm resisters to 8 ohm on the entire A-B-A set to prevent future issues. Sound right? Anything else preventive I should do?

I am leaving for a week vacation today but will use the time to find a repair shop forum sponsor and then ship the unit(s) when I return.

Follow up for those interested.

Looking at the AC regulator, it didn’t look like it would be too hard to replace, so I ordered one from Lionel, and I just finished installing it.

Short ending: the engine responds correctly and works fine. The regulator was clearly the problem as the gurus above thought. Thanks all for the great help again.

Two questions for the crew:

1. The regulator has sort of a black tab with electronic connections on it. On my matching B unit that tab is screwed to the frame with an insulator between it and the frame. On the A unit I was working on there does not appear to be a similar mounting hole, so I did not screw it down. Should I have? And what is that black “tab”? See the “long ending” below to learn why I couldn’t just match the old part.

2. Where is the 6 ohm smoke resistor that I see a lot of posts about? I thought about replacing it with an 8 ohm resistor as suggested, but I don’t see it. Is it inside the smoke unit? What is involved in replacing that?

Long ending: I ordered the part as shown above in this thread, which is exactly what Lionel showed in the parts view for this engine. But upon disassembly I quickly realized that someone had repaired this before, and used a different regulator part! It didn’t look like the new part, and had a different number. They had used shrink tubing and simply spliced all the wires matching colors. I probably should have done the same, but decided to use the pin headers as provided on the new part. Luckily I also have the matching non powered B unit so I opened that and used that as a reference. The only tricky part was adding the brown wire from the other electronic module to the pin header that goes to the truck, but I figured that out well enough. I will say that in this case working with fine gauge wire and small connectors, being near sighted was an advantage.

First off, the black tab is the smoke triac, and it most certainly should be secured to the chassis with the proper insulating pad and screw.  I just drill and tap a 3mm thread to mount it if there isn't one.  That is vital for the health of the triac, without proper heatsinking, it will quickly die.

The 6-ohm resistor is indeed in the smoke unit, and should be replaced with an 8 ohm one or you'll be replacing the regulator again in the near future.

Thank you John. Just ordered the screw and insulator from Lionel as per the exploded parts diagram. There are two unused threaded holes on the frame back where the regulator sits, so I am assuming the screw fits those holes.

The resistor replacement bears some thought. Probably more of a job than I am comfortable doing since soldering is involved. But man, that makes for an expensive repair if I need to ship all three units to a shop.

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