MTH Smoke unit repairs

The simple way is to unplug the fan and connect a 9V battery to it briefly, if it spins it's probably OK.

You might also test the voltage coming to the fan motor when it's supposed to be on and see if it's getting voltage from the PS/2 boards.

If the motor checks out OK, make sure there is continuity from the smoke motor wires to the four wire plug on the circuit board, sometimes the tender tether will have an open between the wire and the plug on the back of the loco. If the motor checks out OK, and there is continuity between the wires on the motor to the plug on the circuit board, have your board tested at an ASC that has a Protosounds 2.o board tester to make sure the FET for the smoke circuit on the circuit board is functioning. 

Marty, I test fan motors with 3VDC from a bench supply, but I try not to assume everyone has that available.   I agree, the most common failure is usually the fan motor, I have a couple of spares nowadays...

Good thing to have handy John.  I get anywhere from 1-4 each week.

An easy and cheap way to make a 3vdc test power supply is to get a 2-AA cell battery bracket from Radio Shack or your favorite electronics supply. 

Thank you for all the replies.

The lowest D.C. voltage that my bench power supply has is around six volts. The motor runs at that voltage.
But as has been mentioned, a bad motor will often run when it is supplied with excess voltage.
It sounds like the motor is designed to run at three volts.
Before I do anything else, I am going to try running it at three volts.
If the motor is OK, I guess I can check for voltage at the contact pads on the chassis.
If there is no voltage then the problem is probably beyond doing with the tools / test equipment I have on hand.

I see two different motors listed on the Lionel parts list. (They have different mounting holes) Some posts I've seen make it sound like a Lionel fan motor will fit the MTH unit. Is that true?

If the motor won't run at 3V, it is bad, I've never seen a good one that won't run at that voltage, and most of them will run at 1.5V, the lowest voltage my bench supply puts out.

CW,  Measure the resistance of the fan motor unconnected.  If it is about 12 ohms it probably is ok.  You can rotate the impeller and measure a few times.

Since this uses springs and contact pad to pick up power to the smoke unit you need to make sure the spring is contacting the pad.  I haven't had trouble with steamers but you never know.

I believe the MTH motor is considered better than the lionel motor.  Some times the orientation of the Lionel mounting holes are different and the motor will be at an angle, so hard to say if it will work.  G

More likely a wire has broken in the harness.  So with the tender and engine shell off test continuity between the pads that power the fan motor and the 4 pin connector on the PS-2 board, with the harness connected to the engine.  Gray and Green wires.  G

The MTH motor and Lionel 610-8057-220 motor are the same.  They are designed to run on 5 VDC not 3V.  That is the motor MTH has been using from day one.  This is the motor C.W. has in his locomotive.  A few years later, both Lionel and MTH started using the shorter motor.  The Lionel number is 610-8057-240.  This motor is about 5/32 shorter.  Same 5 VDC.  Lionel currently is mixing the newer motor with diagonal screw holes (610-1154-130)  into the current locomotives.  This is made by Mabuchi.  All motors run on an acceptable voltage of 4.5 to 5.5 VDC.

John is correct on a good one running at 3V.  If your motor will run at that voltage, you have a good one.  Luke is correct in checking continuity from the board to the motor.  If you l;oose continuity along the line, it is easy to pin point your issue. 

I figure, being a standard DC motor, if they won't run on 3V, they're pretty likely going to be unreliable even on 5V.  I tried both new ones I had, and a couple on existing smoke units, and all of them would spin on 1.5V. 

My most observed common failure is they develop bad bearings and bind up, most likely because the smoke fluid isn't that good a lube.  Running them on low voltage gives a good indication that there isn't excessive friction in the bearings, saves me from opening up the smoke unit.

I confess, I'm a cheapskate, and for my use I'll try lube of a bound up motor.  If I'm fixing someone else's engine, I put in a new motor.

John, that works ok.  I think it was you a while ago that talked about a drop of oil on the motor shaft.  Great thing to do even when installing a new motor.  I have a friend who wants every loco done that way. 

Once again, I appreciate all the comments.
The fan motor does run at three volts.
I checked for voltage at the contact pads.

The good news is that all three pairs that have wires running to them are OK.

But the engine still does not puff. (I can see smoke vapor in the stack when it is running up on blocks)

I looked inside the smoke unit.

The wicking is already burnt a bit. The opening towards the fan seems to be clear.

I am not positive, but I think the fan may be running.

The gasket material has a big bubble around the area where the resistors (heaters) are located. Could that be blocking the air flow?

Also, when I originally disassembled the smoke unit, I erroneously separated the cover from the fan chamber. The gasket crumbled, so I used some Permatex form-a-gasket to seal the fan chamber to the lid.
I didn't think the seal would be critical, but maybe that is the problem.

I know the wires to the motor are OK because I ran it from the contact springs.

I also cleaned the pads and contact springs with a little Craig Deoxit on a Q-tip.

I guess the problem could also be contact between those springs and the pads.

Not certain how to check that.

The lights are OK, and the heater working.

The seal isn't all that critical, it mostly keeps smoke from leaking inside the shell.

You should be able to hear the fan running if you put your ear close, at least I can and my hearing isn't the greatest.

I'd measure the voltage across the motor when it's supposed to be running.  Since you have tested the fan, checked the wiring, next step would be to see if the fan is getting power from the board.

Does this engine chuff when running?  Does it smoke in neutral?

The other things to check is that the impeller is not loose on the shaft.  A drop of super glue will fix it if it is.  All this is based on you saying you have good voltage at the contact pad.  It is pwm power. 

You can use clips to the springs and touch the pad to see if the motor spins.  Just be careful not to short anything.  G

G, I never thought about the loco smoking when running. If the tach reader is bad, it will smoke when sitting still, but when the loco starts running, the smoke stops, as there is no pulsing of the smoke motor. Also, the chuff goes away and there is no speed control. Running in conventional, few notice the speed control not working, but when running in DCS, it becomes apparent quite quickly. 

I will probably take another look at the locomotive today.

The engine/tender does make chuffing sounds. When I had my vom on the fan motor pads, the voltage did pulse up and down.

I am going to see if there is a way to check continuity (or the presence of voltage) at the fan motor while the cab is on the chassis.

Working on postwar smoke units certainly is a lot simpler

CW,  If the engine chuffs when moving then the tach is fine.  Since you have voltage at the pad, and the motor does spin when you apply power, you really can only have one of 2 issues.

The fan impeller is loose and the motor spins but no air is moved, or you have no contact between the pad and the springs/connector of the fan motor.

If you power the fan from the springs and watch the impeller is it moving so fast you can't see if spin, or can you see it rotate slowly.  If slowly the impeller is loosed.  This also lets you know the connector plugged into the springs is making good contact.

At that point the pad and the spring are not making contact.  Either stretch the spring, or add thin washers under the pad to raise it.  Make sure shell engages completely with post when screwing down.  G