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Minitrix Fairbanks-Morse H-12-44 help fitting decoder please

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  • Member since
    May 2006
  • From: UNITED KINGDOM
  • 64 posts
Minitrix Fairbanks-Morse H-12-44 help fitting decoder please
Posted by iomtt on Friday, August 29, 2008 3:31 AM

Hi All,
A Minitrix N switcher has been in the box for a while waiting for conversion to DCC last night i decided to give it a go, first off the contacts to the wheels in each bogie were set to be on the same side of the track so i carefully removed one and reversed it to pick up on the opposite side leaving them diagonal.
On to the chassis it was cut to accept the decoder, the motor wired as per usual covering parts of the chassis where contact may be made motor/chassis,
the wires to track were fed and soldered to a tab coming from each bogie.
After several tests on the prog track with  my NCE Procab i couldnt get a read from it, the only thing to cause this i can think of is the chassis is a one piece metal type, and the bogies are held in place with metal pins that pass through metal cast bogies could this be stopping a readback ?
It is not the most detailed little shunter but would make a good addition to the stock.

The loco is  the  one  here ...........

http://www.visi.com/~spookshow/h1244.html

I would  be  grateful  if  any  of  you  have  converted  this  loco  and  could  tell  me  how  to  wire  it  for  dcc.

Many  thanks.

  • Member since
    October 2002
  • From: City of Québec,Canada
  • 1,258 posts
Posted by Jacktal on Friday, August 29, 2008 4:56 PM
You say you modified the electrical pick-up pattern...wich raises a question to my mind.Was it running on DC before?If it was,it is likely that those contacts were designed to be on one side together and that the other polarity is carried through another type of pick-up device,possibly through the truck pivots.In short,if it did run before,it is likely that you have created a short and it is obvious that you won't read anything.Just a guess......
  • Member since
    May 2006
  • From: UNITED KINGDOM
  • 64 posts
Posted by iomtt on Friday, August 29, 2008 6:44 PM

 Jacktal wrote:
You say you modified the electrical pick-up pattern...wich raises a question to my mind.Was it running on DC before?If it was,it is likely that those contacts were designed to be on one side together and that the other polarity is carried through another type of pick-up device,possibly through the truck pivots.In short,if it did run before,it is likely that you have created a short and it is obvious that you won't read anything.Just a guess......

Hi  Jacktal,  

Yes  i  did  move  one  contact  to  pick  up  of  each line  of  the  track as normal in  DCC  thinking  it  would  pick up of  each  side of  the  bogie,  this  works with  a  split  chassis  of  course  but  not  in  this  case,   the  loco   worked  fine  with  DC    power so  i have  changed it to   the right  hand  side  for  the  red  wire   on  both trucks as it was  at  first  on DC and   need  to  determine where the  black  wire is to pick  up power now.     

  • Member since
    October 2002
  • From: City of Québec,Canada
  • 1,258 posts
Posted by Jacktal on Friday, August 29, 2008 10:04 PM

That's what I thought.However,since I'm not familiar with this particular model,I can only try to help you with what I'd call generic information.First,you'll have to carefully dismantle the engine and slowly follow both electrical paths.Looking at the picture (Spookshow's),I'd say the whole frame is the return path (or negative) while the red wire goes straight to the motor,completely insulated from the frame.

It may be a challenging DCC retrofit but almost everything is possible with a little patience and a good procedure...and it is even more rewarding when it works.

First,you'll have to check if your motor is insulated.You can check this by touching an Ohmmeter probe to the motor housing then the other probe to your red wire(wich is likely +) then repeat again touching the negative terminal -(possibly a black wire but some manufacturer use a tiny spring to induce contact in the case of frame ground).You shouldn't get any reading on either,if so you motor body is conductive and you'll have to insulate it from the frame by wrapping it in an insulating material.BTW,if you test between your power contacts,you'll have a reading wich is OK.

If your motor body isn't conductive...then good.You'll have to remove whatever is linking the motor to the frame (either a small spring or brass tab or else) and weld a small wire to the motor in place of this contact to reestablish your return path wich will be linked to one of  your decoder's "motor feed" wires.NOTE:be absolutely sure this wire or your welding do not touch the frame and make contact,an instantly fried decoder will result.You may have to enlarge the cavity in the frame in this area to do so.Then bring this wire to where the decoder will be (you may have to drill a small tunnel for the wire to go through the frame).

Then you will have to cut the red wire and bring both ends to the decoder (you may have to lenghthen it) then reassemble your motor and frame.This will give you your four links you need:the two wires to the motor (one red,one black) and your two rail powers (the other red wire and the frame itself.If you haven't fried your decoder yet (wich I fear),this should work.

Installing the light should be a breeze if room allows but you'll need a resistor to do so and I'll let other people tell you wich one you need.

  • Member since
    January 2007
  • From: Eastern Shore Virginia
  • 3,290 posts
Posted by gandydancer19 on Tuesday, September 2, 2008 5:50 PM

I have had two of them, just like the one you have shown in the photo.

Both power trucks are wired or have their pick ups mounted the same way when sitting side by side. This is an all wheel drive and all wheel pick up loco and was the best available for it's time, and in MHO still is.

Conversion to DCC is not too practical because there is no room for the decoder. I converted mine to TT scale narrow gauge box cabs by building another body. Then I had room for the tinniest decoder they make, and it still was not easy. You have to isolate the motor brushes from the frame and the pick up wire. Then somehow attach a wire to the frame so you can connect it to the black wire on the decoder. The other wire that was going to the motor goes to the red wire on the decoder. Then the orange and gray wires go to the motor. The decoder or orange and gray wires also must not touch the frame. If you don't do it right, you will blow the decoder.

Elmer.

The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.

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