JLC Big Boy smoke unit

I had the same issue with mine years ago, ended up being a bad crimped terminal plug between the smoke unit and motherboard. Id check there.

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.

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.

I just had a problem with a very similar smoke unit on my Allegheny.  John helped me and told me to replace the resistor with an 8 ohm and new wicking.  Works great!!  Smokes really good.  His insight was so helpful.

Hi John, and everybody else.

The old resistor was 6 Ohms, but I did have a brand new 8 Ohm resister, installed it as per your directions, screws tight, resistor not touching the chamber body, did not heat up, also checked voltage at the resistor mounting screw heads, got nothing

What do you get at the connector?

I suspect the regulator module.  With this smoke unit model, the heater voltage doesn't power the fan, the smoke unit gets 3rd rail direct to power that logic chip that controls the fan.  The smoke heater is powered directly from this module, which is almost surely bad.

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.

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. 

The PCB is available, but it's pretty clear from his photo that there's nothing wrong with the traces that go from the connector to the smoke resistor.  That being the case, it's pointless to replace the PCB, that isn't were the problem is.

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. 

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

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.

Thanks John, I'll let you know how I make out.