Lionel Multi Unit Smoke varying output

Top suspect is the Smoke control board, all the smoke units don't crap out at one time.

Thank you John, have you seen the board do this type of thing before? I will get one on order.  Just curious.

I've had that board fail in the same locomotive, but I had no smoke at all.  In non-vision line stuff, I'd also had a number of the voltage regulators fail.  I just wrapped one up, did the same thing.  Smoke was great for a spell, then then fall off as it ran.

I'd actually start by looking for any connection issues, defective connectors, etc.  Anything that limits the current flow to the smoke units will cause this.  Since you have multiple smoke units, there's a fair amount of current flowing, bad connections can be a real problem.

Yep, I've been down that path at least with verifying the connections. One of the things bothering me was wherever the control signal came to the board to control smoke output (low, medium, high). I was wondering if maybe there was another board that sent a digital signal to the smoke board IC or voltage or whatever to make certain the correct board is replaced. Varying the output from the cab doesn't seem to make any difference. I'm assuming you can't get a schematic on these things. You're a wealth of knowledge and really appreciate your help!

The serial data comes to that control board, which is how it decides when to run what motor and smoke unit.  The simple smoke regulator in single smoke unit engines also gets serial data to control smoke volume.

Schematic?  You must have been a comedian in a former life!

Rola1 posted:

Is there a current limiter (on watchdog timer) or something else that is causing the issue or is this normal or?

Does this loco have thermistors? It sounds like thermistors positioned too close to the resitor .  

John, your the expert here.

The older VL Challenger is the modular boards, it doesn't have the thermistors, those are in the newer stuff with the RCMC integrated electronics.

I'm going to replace the board as John has said he's seen a few of them with problems. Calling Lionel is like calling a proctologist, you just don't want to do it. Hour wait on hold today and will try again tomorrow. 

I will post the outcome once I get the board. 

Once you've addressed any potential issues with smoke units, that's the next step.

Did you check the screws that hold the smoke resistors?  I wonder if they're working their way loose, that will cause you to lose smoke as things warm up.  Hard to believe all of them did that, but before you spend money, might as well check the free stuff.

Yes, I replaced all 3 resistors, dual smoke and injector with batting. Built new gaskets too since unavailable from Lionel. Pretty much a complete rebuild of all. It will smoke however it's weak until you turn the smoke off and then immediately back on it smokes great for about a minute then weak, turn off and immediately back on, it's back smoking great then process repeats

Sure sounds like the regulator circuit isn't working properly.  That's a classic symptom, for some reason the uP just "forgets" the smoke level setting and starts dropping it.

I've actually put a couple of the regulators on the bench to see if I could make them work, but I've never been successful, I think the little uP is losing it's memory from the heat of the smoke regulator, only thing that seems to make sense.

That makes perfect sense. 

Update

I replaced the smoke control board and it's doing the same thing as before. From the measurements I've taken it appears the smoke circuit increases resistance to ground after about 20 seconds on the return (- side of the smoke element). I get about a 5vdc voltage drop across the element(s) at start up or alternating smoke off/on and it smokes great but after about 20 sec the voltage drop starts to vary between 1.8 and 2.6 vdc. The supply side is rock solid at 8vdc as well as the ac input to the rectifier. I also removed the command base and checked it conventional only with the same result. Going from low/medium/high on the legacy remote really doesn't show any difference on smoke output and maybe .2vdc difference across the smoke element. Does the RCVR board control the serial data to the smoke control board and could the RCVR be bad (I've already ordered one from Lionel - I'll have a spare if doesn't correct it). I'm stumped....

Well, the TMCC receiver does receive the TMCC signal and output the serial data, it's where the commands to the smoke control board originate.

It's worth a shot right? Have you seen or have a guess what the voltages should be between low/medium/high? And thanks for your help on this!

It's pretty hard to measure those voltages with a multi-meter, they're chopped waveforms.  Even with a true-RMS Fluke, I don't get readings that are all that accurate for smoke regulator output voltages.  The only way to really see what you have is with a 'scope.  It is normal for the voltage to start higher and then drop off, that's a fancier version of what TMCC does, full track voltage to "preheat" the smoke resistor, and then drop down to normal voltage.

Since you already have the RCDR coming, can't hurt to drop that in.  If that doesn't do it, I'd be looking for wiring issues, damaged connectors, etc.

I've got one (HP handheld). I'll capture before and after with the RCVR change and let you know what I get if your interested.

And if that doesn't do it, it's coming to you!