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I have a MTH steam locomotive that I recently upgraded to Proto 3.0 and am having an issue with the smoke feature.

The engine and Proto 3.0 upgrade have operated flawlessly for approx. 32 hrs. of run time. It was operating fine one day and when activated the next day the smoke feature no longer worked from startup. The smoke unit heating element is operating (it is heats up when smoke is activated) but the fan is not. I have done the following troubleshooting:

  • Checked continuity of all wiring from the Proto board to the smoke unit fan and all is OK.
  • Checked fan motor with 1.5 volt battery and it operates
  • Measure voltage from Proto 3.0 board at the connections to the fan motor and it is.4 volts constant when the smoke feature is on. It does not pulse whit chuffing.
  • All other functions, including operation of locomotive drive motor, sound, lights, etc. are working as expected.

Seems like it might be an issue with the Proto board.

Anyone have any ideas other short of complete board replacement?

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Thank you for your input Gunrunnerjohn!! It is greatly appreciated!!

I do not believe that there has been a short to ground of the wiring (I don't see any evidence of this and have been very careful with the wiring, but I guess it remains a possibility).

Is there a process for testing the standard steam PS32 upgrade board?

If the smoke fan FET is toasted, is that a part that might be replaceable without having to replace the entire board?

The process of testing the board would really require the MTH test set, it's treated as a PS/2 board for purposes of testing.  This allows us to exercise all the functions of the board.  The smoke FET is a part that can be replaced, it's a currently available part.

First thing to do, if you haven't already, is measure the smoke motor leads to frame ground.  There should be no continuity to frame ground for any PS2 or PS3 signals except the actual frame ground connection to the board.


Images (1)
  • mceclip0


I just tested the smoke motor leads for continuity to ground (with the tender plugged into the loco and and no power) and found continuity which fades out to an open circuit over a period of 3-4 seconds. After disconnecting the Multimeter probes and waiting 30 sec. +/- this can be repeated 3-4 times before it goes to a continuous open circuit.

I also checked the resistance across the smoke fan motor only and it measured 11.8 ohms.

Does this info. lead you to any other thoughts or suggestions or would the next step be to have you test the board?

Below is a photo of the boards as installed in the tender (just wanted to make sure we are on the same page with the type of boards we are talking about)

proto 3 upgrade


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  • proto 3 upgrade

That's the PS32 board, that's what is in the standard PS/3 steam upgrade.  If the leads from the smoke fan have continuity right to the smoke fan connection on the PS32 board, and the smoke fan motor runs when tested, the next logical step is to check the PS32 board independently.

One thing about testing the smoke fan motor.  It should not draw more than about 40 milliamps a 5VDC.  If you have a way to test that, that would be worthwhile.  You can get failures like this if the smoke motor is bad and draws too much current, I just replaced a smoke motor for that very issue.

So I rechecked the leads from the smoke fan motor to the board and they both have continuity.

Based on all of this I would like to send you the board for testing and repair (if possible). What is the best way to send this to you (address, etc.) and could you give me an idea of potential costs? Can I send you the boards only to minimize labor,  packaging and shipping costs?

One other quick question though. You mentioned that failures like this can occur if the smoke fan motor is bad and draws more than about 40 milliamps at 5 VDC (I am not able to test the motor right now--need a 5VDC power supply which I can borrow from a friend sometime in the next week or so). When you refer to failures like this (with the information that you have at this point) are you thinking that this is a fan motor issue due to high amp draw or a board or FET failure caused by a high amp draw from the smoke fan motor? Either way, it seems like in addition to having you test the board I need to test the fan motor for amp draw and if it is high replace the motor.

Thank you again for all of your help!!

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