Inop smoke fan on Decapod

If wires and the connectors are all fine, pins not pushed out, then a FET on the board could have opened.  Of course I would still try changing the fan motor first.  Sometimes they run at high voltages but not at the pulsed voltage from the board.  G

GGG can confirm this, but I believe you can measure (carefully!) the DC voltage across the 2 smoke fan pins (on the 4-pin smoke connector) right on the PS2 board itself.  Irrespective of whether you have a broken wire problem between the PS2 board and the smoke fan, you should be able to measure the fan voltage at the board.

At engine idle the voltage should be some steady DC value less than 5V as the fan is on at some slow speed.  When chuffing, you should see the meter jump with each voltage pulse synchonized to the chuffing sound.  If you get no voltage across these 2 contacts, then I'd think the FET.

A simple test is to just put a small incandescent bulb across the smoke fan output.

Dave,  With the tender harness plugged into the engine with tender and engine shell off.  Did you check continuity from the gray wire pin on the rear engine PCB to the gray wire in the 4 pin connector on the board.  Also the green wire?  Sometime a wire inside the tender harness breaks and that causes the loss of an item.  In this case since the engine runs I am thinking the green return, not the gray 5VDC.  G

No I did not check continuity from the rear of the engine to the board, but that sounds like a good idea.  The problem is when you remove the engine boiler, the smoke unit is in the top of the boiler and not attached to the chassis.  I would have to lay the boiler on it's side next the chassis on a 'hot' track and hopefully have just enough wire length to do that.  Also, the plugs on the PS2 boards are mounted upside down on the tender so they aren't easy to access.  Like I said, I think am giving up on this one.  I'm doing this as a favor for a friend and I don't want to ruin his engine.  

You can bring the engine over the mountain to Ed and have him give to me to test the board. It will eliminate a lot of guessing to know if the board is bad or not.

GGG:  Okay, understand now what you are saying.  May give it a try. I still have the tender shell off so it should not be too difficult.  Thanks. 

Could someone tell me where the FETs that good bad are on the board and which board are they on?   A picture would be terrific.  Would it be better to just upgrade to the 3volt boards and speaker?  Thanks.

Forest: Thanks for the offer, need to speak to the owner and see what he wants to do.  

If you turn the board over so you are looking at the bottom, the side below where the connectors plug in are 2 small FETs for smoke fan on and pulse.  They are near the edge and bottom.  Most likely this can be repaired easily, which is much cheaper than going the 3V route.  I can test and repair the board if it is a FET issue.  G

Under the connectors on the bottom is a sea of small FETs, does anyone have a map of the functions? 

"near the edge and bottom" doesn't actually tell me where they are, I'm not sure what you consider the "bottom".

Here's a picture, which of the parts can you identify by function?

I'm guessing it's buried in that book somewhere.   We rushed through a lot of stuff in the two days, and component repair was way down on their list as most of the folks in the class did not want to attempt it.

I'd like to find a map to all the outputs to components.  I guess I could just generate one with a meter and a little time...

The old gray cells are waking up, I found the component repair section in the ASC book.

Chapter 4 has the diagram.  G

Yep, note my edit, I decided to take a look.  I though I had seen it.  

Where do you get the FDR6674A parts for the 3V board battery circuit?  I have one with that issue, and the resistor checks out.

I don't have your Chapter 4 diagram but the smoke fan FET output is on pin 2 of the 4-pin smoke connector.  The square pad of these connectors denotes pin 1.  Perhaps you meant 3rd pin from the left in GRJ's photo.

The 2 FETs are circled.  The other signal to the fan motor is pin 4 if one were ambitious enough to measure the pulsing/varying fan voltage.  Obviously the remaining 2 wires (pins 1 and 3) go to the heater resistors.

Thanks for those pictures and explanations.  My friend is willing to live without the smoke for now.   Thanks for all your help, GGG, Stan and John.  

Did you get to check the harness, that is always a high probability.  G

Obsolete part no longer available.  There was a place with an alternative but the minimum purchase and shipping would push $100.  G

Found it, no longer unobtainable, Digikey.

FDS6670ACT-ND MOSFET N-CH 13A 8-SOIC  $1.33/ea

I found that as a listed replacement, but I didn't check the pinouts.  Obviously, it's not a "direct" replacement.  Low class to discontinue the part without some sort of replacement possibility...

John, I spend a year looking for the item. It truly seemed to be a one of a kind pin out at that size of chip.

If you want me to fix the PS send to me. Will give you a tech to tech discount.  Normally the trench doesn't go.  MTH Service documentation on this is not really correct:-)  G

G

George, I really just wanted a couple in stock so that I'd have them.  However, since they're unobtainium, I'll just skip that part.   I'm trying to get a few of the common parts, I have several board sets that I'm going to tackle and try to get working.