Bench testing Lionel Legacy smoke unit

Hi,

That unit uses an 8 OHM resistor as a heating element. I cant imagine you would need much more than 6V to get decent smoke for test purposes. The fan is always 5V DC. I would test them individually and use a meter to test the resistance value of the heating element. If they both work individually they should work together but I don't know what voltage goes into that specific smoke unit. It looks like a three pin connector to the unit of which one looks to go directly to the heating element and another to what looks like a voltage regulating circuit for the fan. I cant tell where the last trace goes as the picture is blurry.

Hope someone can help fill in the last blank to your puzzle.

Thanks!

I think the fan has a 5 vdc regulator in front of it. So you put the 6 vac on the resistor and about 10 vac or so on the lead to the regulator . The third lead is common to both. It might work to put the 6 vac on both.

If it was me, I would put the smoke unit back into the engine and test it on the layout with the shell off.  I see no need to test the parts separately. If you put a meter to the resistor and get an 8 ohm reading, the resistor is fine.  If it blows smoke when you turn the unit on, the fan is fine.  You risk blowing the board by putting voltage directly to the board if you touch the wrong contact/trace/solder point.

Anytime I bring an engine to my bench for maintenance, I always inspect the smoke unit.  I replace wicking if needed and the resistor if its not reading correctly on my meter.  I then put it back in the engine and test it with the shell off.  If there is a problem, its only the smoke unit screws I need to undo to make adjustments.

Here is the smoke unit from a6-28540 Tunnel motor.  I bought this loco  6 months ago at the proverbial good price...

When the unit is on the layout, the fan works (I can feel the air movement)  but it appears the resistor does not, since no smoke.  I disassembled as the pictures show and tested the resistor -it is good.   The two pin connector goes to the dc fan motor.  Does anyone have an idea what the 3 pin inputs are and the components?   I would like to test the board with the correct inputs to try to figure out what is bad.  The power supply components look like my soldering skills could support replacement:  a standard diode, 1 micro farad and 100 microfarad capacitors, and an LM78L05ACZ regulator.  I can't find any circuit information but seems logical that the capacitors, voltage regulator, and the diode are the power supply for the fan and resistor.

BTW, in case you are wondering what that aluminum sheet thingy is, it looks like someone over the years decided the voltage regulator needed a heat sink!

There have been a few other threads on this smoke unit but I don't see what I am looking for on the pin out for the 3 pin connector. Any other advice or guidance is certainly welcome in troubleshooting.  Obviously, no replacement items are available.

Most smoke units that have a 5v regulator on board just need about 12v to power both the resistor and motor. On the three pin connector one pin is ground. Sometimes  the two outside pins are tied together, in which case connect power to one of the outside pins. On others you have connect power to both outside pins if there is no on board jumper.

Pete

Thanks Pete, sounds like I can't hurt anything so I will give those options a try.

Reporting back after testing completed. It is hard to see the traces to identity the exact circuit, but it appears one of the caps is bad. Can't find my solder wick so ordered another roll.