FEF-3, 30-1600-1 shorts when activating smoke

Basic notes on PS2/PS3- and my thought process on how I would troubleshoot.

#1 chuff signal and timing is generated or derived from a count of pulses from the tach reader- not a cam switch or magnet. Thus typically it is somewhat random starting position compared to a given wheel position. I'm saying because lets say a traction tire was rubbing a brake shoe in a certain spot of the wheel. That may or may not correspond to the exact timing of the chuff and in fact will sometimes be in sync and out of sync.

#2 Specific to PS3, there is a boiler board that controls the main motor, as well as the lights, the smoke fan motor, and the smoke heater. In addition, this board and processor has 2 serial data lines- transmit and receive. It transmits the chuff signal back to the tender board to trigger the matching chuff sound. It in turn gets its commands for speed, lights, smoke on off from the tender board.

Since it only does it with smoke on- typically, that would eliminate a mechanical bind (example traction tire rubbing a brake shoe, an eccentric crank not clocked properly and jamming the linkage- or some other mechanical periodic friction bind).

Since the smoke heater is more or less constant, this implies the smoke fan motor that pulses and chuffs is somehow drawing excessive current and thus taking some power away from the main motor drive.

So testing:

I would specifically unplug the smoke fan motor, but leave the smoke resistor plugged in (green connector unplugged (typically green and grey wires going to fan motor, red connector plugged in typically purple and brown wires) note both plugs may be white, I'm just referring to some semi standardized colors one might find. Trace where the plug or wire goes to final endpoint in determining what plug is what.

If it's still doing it with the fan completely unplugged- then suspect possible pinched wire in the harness for boiler board to frame ground or other short, or worst case a bad boiler board. Because boards are hard to come by right now from MTH parts, this might be one of those last resort- try reflashing the chain and sound files- with the engine and tender together to ensure the boiler board also gets any associated firmware chain files updated. Again, given the problem, I would do that with the smoke unit (resistor and fan) unplugged just to not potentially cause an issue while programming.

Just further reviewed since this is a railking, there doesn't appear to be the possibility of tire to brake shoe rubbing. That said, check the eccentric crank linkages to ensure they are tight, but also clocked or positioned so the linkage point is near the middle of the wheel and not flipped or rotated out causing longer stroke of the link rod potentially jamming it.

Here is hoping it is mechanical and not electrical.

Top suspect is the smoke fan motor drawing excessive current.  The fact that it happens in time with the chuff is a key symptom.  The smoke fan runs of regulated 5V power, and if it draws too much power, it can affect multiple aspects of running.

Thank you for you excellent suggestions gentlemen. Since I have had this loco since about 2013 and it has had this problem for most of the time, it seems the most likely problem is a bad boiler board. Remember that I stated I have installed a different smoke unit (and therefore a different fan motor) and it behaved in exactly the same way. To be sure I will disconnect the fan motor and see what happens.

John T.

I've posted a picture of the inside of the engine. There is no plug for the smoke motor between the motor and the board. The smoke motor wires are the gray and green wires at the far left in the picture, on the plug with the small wires, almost hidden in the shadow. I will need to un-solder the wires from the motor to disconnect it. BTW, it behaves the same with the shell off as when it is on.

Just replace the motor.  G

Curious as to why replacing the motor would help.

John T.

@JPThut posted:

Curious as to why replacing the motor would help.

John T.

The symptoms STRONGLY suggest that the smoke fan motor is drawing excessive current.  Replacing it would obviously fix that if that's the case.

Note that if you simply disconnect one lead from the motor (make sure to insulate it), and then run it, you can find out if the smoke motor is the cause.  If the symptom goes away, it's the smoke motor.

Duh, I first thought of the engine motor which is why I made the most recent statement. I plan to un-solder one of the smoke motor leads but haven't had time yet. (Honey-do list is long!)

OK, it does not short with one lead disconnected, BUT where do you find a fan motor to buy??

MTH Parts & Sales

They list them as out of stock as do other train shops. I have checked quite a few.