TMCC Smoke Unit running too hot

I don't have a good answer for you, but a reminder to list the train number too (on cab or number boards), for better, faster responses.

Basically, diodes, or a regulator is likely cooked. 

We need a number.  FYI, normal voltage is 9-12V rising to 14V when you hit the 9 button.  Many of those engines are controlled by an AC voltage regulator.  I think that is what you have and your reg is bad.  Until you get to the bottom of the problem, pull the white Leoco plug on the smoke unit.

If this is one without the regulator, the likely suspect is the R2LC smoke triac.  It's the larger package next to the connector.

If this were a model with the regulator, the 6 or 8 ohm resistor would have gone up in smoke long ago with full track voltage on it!

That circuit boars is definitely in the locomotive. Thanks for that information. The locomotive is a Southern Pacific 4-4-2 Atlantic (6-28070).

Is there a way to actually fix the board, or should I just order another one for $28.

I fix these all the time, it's a simple fix.  If you don't mind soldering on the PCB, the part is cheap.  The 2N6075BG at Digikey is .69 quantity one, and shipping is only a couple bucks First Class Mail.

If you don't feel like soldering, you can send it to me and I can repair it.

That's really great information. I had no idea that these train's electronics were repairable.

Also, when I switch direction the rear headlight doesn't light up and the front headlight stays lit, so I'm leaning towards just replacing the board. It seems like something bad happened to the board. But, maybe I should try replacing that triac and the rear headlight transistor (is that a transistor?) first. 

I can confirm that the replacement of a smoke triac is a simple job. A couple of years ago I had a smoke problem with a K-Line Berkshire. I posted here and Gunrunner John guided me through the diagnosis and provided the same Digikey part number, which I ordered and installed. You need to be careful but anybody with decent soldering skills can do it. One piece of advice, for this or any other work on a PC board - use a low powered soldering pencil with a narrow or pointed tip. Mine is a 12-watt (that's right, TWELVE watt) Weller and it provides plenty of heat for replacing PC board components. 

Another piece of advice - double check for shorts in the smoke unit. That engine has an old-style puffer smoke unit and the feed to the heater element can get grounded out against the body if the insulation is damaged or out of place. That happened on the Berkshire I mentioned above, and the short was the reason the smoke triac blew. 

With regard to the backup light issue - try a full reset of the TMCC before replacing the board or changing any components. Those sorts of bugs can often be corrected with a reset. It might or might not work, but it's cheaper and easier than changing parts. Also, be sure all the boards and connectors are well seated. For some reason, things tend to come loose on that particular model. I've had two of them and they both had a habit of loosening up no matter how carefully I set the boards. 

If you diagnose the board light triac as bad, those are also replaceable and also quite cheap.  They are a bit harder to get to.  I normally just bend those back and forth and break the leads, then suck out the little bits of leadin the board one at a time.  I actually do that for smoke triacs as well, it's not like you have to save the old part.

The reset is the first thing to try, for that locomotive the reset code is AUX1-4, steamer with smoke.

If you are unfamiliar with removing components, these types of products will keep the desoldering from sucking, by sucking

 http://www.amazon.com/Parts-Ex...dering/dp/B00QTGEL18

I go for the express solution for desoldering.

Unless its a lookalike, the one in the link can have the piston o-rings replaced if it splits, or gets cut by slagged solder. The piston has an a Allen head hole dead center and unscrews.

Oh your gonna love this one if your near sighted GRJohn.......

.... and the recessed thumb press plunger, keeps me from knocking my glasses off my face when it pops up . (and saves me from gasping in flux fumes trying to catch them without burns to them.... or me) 

I feel your pain, I had one that had the exposed plunger, and it was deadly!   I have the mini version of this one for finer circuit boards, it's not so rough on them when you suck stuff out.

I always thought they should be a bit smaller really, but I have somewhat small hands to begin with.

Here's the "small" version.  It's handy, but it doesn't have the sucking power of the big one.  This is good for more delicate circuit boards.

Just installed the replacement circuit board. Smoke unit turns on and off and reverse light works now (front light doesn't turn off). However, I can only get 17.1 volts or off. If I press <eng>1<aux1>8, then it turns off. If i press <eng>1<aux1>9, then 17.1 volts. If I hold 9 down, it doesn't boost. I can't press 8 to toggle on/off, because it just turns it off no matter what. I followed the steps to reset to steam engine by selecting option <prog switch on><eng>1<aux1>4<set><prog switch off>.

I must be missing something. Perhaps there's still something burned out? I thought it was supposed to run at 12 volts, and then there was also a boost mode that was 18 volts.

My track voltage is 19.2 volts.

Thanks for your help last time. I think we're making progress.

Best regards,

SacramentoNorthern

FWIW, your track voltage is too high, 19V is the MAXIMUM specified for TMCC/Legacy.  I recommend no more than 18V on the track.

As far as the smoke unit, that's a new one on me.  First thing I'd try is a new R2LC, just to see if there's something really odd with that one.  If it's boosted all the time, that's usually a shorted triac, but since the triac can turn it off, I'm not sure what is happening.