How do I test an MTH smoke fan? What voltage?

IT Should RUN ON 2 VOLTS Dc. just disconnect the leads connector 4 pin connector for smoke unit and apply 2 volts with battery or power supply do not exceed 3 volts or you'll burn up motor if motor don't start replace motor there not that expensive! here is the part number if you need new motor

BE0000041 MTH PART NUMBER!

Alan

The MTH fan motors are 5V motors, but I actually test them like Alan states.  If they won't run on 2 volts DC, then I consider them bad.  Also, they should not draw more than 40-45 milliamps at 5V DC.  Again, if they draw more current than that, I also consider them bad.

The SW switchers have a small smoke chamber and if overfilled will flood the fan chamber, seeping through the top motor bearing, causing the motor to fail.  You can sometimes remove it, spray CRC Lectra-clean into in, relube the bearings and test, as John stated above, otherwise, replace the motor.

Thanks Gentlemen, very helpful as usual. I have it all apart on my desk so I'll test it tonight and see what I see!!

Next question: so conversely, if I have the loco on a test track under power, shouldn't I expect power to the fan? I did that and the heater ramped up but I had no voltage at the fan leads. I thought I check that before I went much further. All the wiring looks very much intact, so there are no outward signs of trouble.

What should I try next? Thanks again gentemen!

Next thing to do is to check the wiring all the way back to the board.  Also, check the two fan wires for continuity to the frame ground, they must NOT have any connection there.  If you have heater voltage for a diesel, it should have voltage to the fan.  Did you check the current draw of the motor, if it's excessive it could pull down the fan voltage.  Of course, it could also be a bad FET on the PS/3 board.

Thanks John, I'll be checking everything again....It all looks pretty nice inside, but quick question: what is an "FET" ?

FET - field-effect transistor It is basically a solid state switch. If too much current is drawn through it (ie. bad fan motor), it can burn out.

@endless tracks posted:

It all looks pretty nice inside, but quick question: what is an "FET" ?

Not something you want to attempt to fix if you have to ask that question!   It's a tiny surface mount component Q209 on the bottom of the PS/3 board.  It's 2mm x 1.25mm in size, and needless to say, soldering the six pins is a challenge with anything but the finest tip iron or a hot air tool.

That is ugly! My neighbor is an expert at SMT and could get it done at work, but I think I'll skip the FET for now and try the less-intrusive. Thanks for all the help!

Another question, if I may: I took the motor out and juiced it with a single AAA battery. It ran fine. Checking voltages, I find there is 1.6VDC to the smoke pot, and 1.6 (on high) to the heating element. Does that voltage sound correct? I've been reading for quite a while and see lots of reference to 3VDC, but I only have 1/2 that.

Does the smoke pot vary just the heat, while the fan would run continuous when the smoke is enabled?

I still have no voltage to the motor leads, so I'm thing the FET is bad as suggested.

Measuring those voltages with a meter won't give you valid results, the power to the fan motor and heater is a PWM bit stream that a normal meter doesn't deal with correctly.

I knew what PWM is without looking it up! LOL. Too bad someone stole my Fluke!  Guess I'm all done with this for the time being. But I did get pretty good at whacking the 3 rail/ 2 rail switch you mentioned in a previous post. Did 4 locos in one sitting....huge difference and no cadavers.

@endless tracks posted:

But I did get pretty good at whacking the 3 rail/ 2 rail switch you mentioned in a previous post.

One of my favorite mods, I've done almost all of my stuff that has those switches.  

So sometimes the motor turns but impeller is loose on shaft and does not turn. Sometimes the gasket swells and stops impeller.  IF the engine has a 2 pin connector for the smoke fan motor, you could plug in a 6V bulb and if it lights the fet is good.  If it doesn't and you have done a reset on the enigne the fet is probably bad it the wires are good.  G

I'm going to go with the bad FET. There are (2) green wires and (1) brown or grey from the motor that all go into the multi-pin connector on the board. A 2-pin connector would be way too easy!

Meanwhile, I'm going to see how long 2-AAA batteries in a piece of shrink tube will run a smoke fan! May get the day out of it. See pics. If it works well, I can easily make this look like an auxilliary air tank, or what have you. Not much else to in these parts this time of year. Seems to run fine...

@gunrunnerjohn posted:

Not something you want to attempt to fix if you have to ask that question!   It's a tiny surface mount component Q209 on the bottom of the PS/3 board.  It's 2mm x 1.25mm in size, and needless to say, soldering the six pins is a challenge with anything but the finest tip iron or a hot air tool1

Thanks @gunrunnerjohn

Just used this info today to repair a PS3 engine that a failing smoke fan motor wiped out the smoke fan FET.

I used the drag soldering method with a fine tip and lots of flux. Not for the faint of heart or poor eyesight.

Also, I took the info from multiple posts and put it into a single document.

From here https://ogrforum.com/...3#133615320936220023

and https://ogrforum.com/...4#133615320937078554

I'm glad this topic resurfaced after many months, along with info on where to buy the FET. Once the snow flies again, I'll be ready to take this on!

Thanks Guys!