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How to install a DCC decoder in a Murphy Model 121 class loco

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How to install a DCC decoder in a Murphy Model 121 class loco. This is the easiest MM loco yet to install a decoder into because it has an opening hatch and a built in speaker for folks who might want sound, so its easy peasy compared to the earlier 141/181 models.

I was asked by a few folk how to do this by way of PM so thought I'd share it here. Perhaps I should have put it in the DCC section.

Murphy Models recommend ESU LokSound V5 or LokPilot V5 21pin decoders, but any 4 or 6 function 21pin DCC decoder should work ok (eg Lenz Silver+ 21 pin). However with the Lenz not all of the lighting functions will be available just the directional running lights. Personally for sound I've used ESU LokSound V5 decoders supplied by WheelTappers DCC sound (Neil) because of their scale like driving characteristics, acceleration, coasting, braking, and the matching sound patterns. Unfortunately the Murphy Model sound project does not make use of ESU's prototypical new 'Full Throttle' driving features, but it sounds pretty good.

  1. Remove the bonnet decoder access cover. It easily pops off (see photo).
  2. Remove the 21pin DC blanking plate - I used a wooden ice cream stick alternating between each side using it to leverage the blanking plate ½ mm up at a time each side so as not to risk bending the pins. Once up enough it will come off using fingers.
  3. Install the 21pin decoder correctly orientated (see photos below).
  4. Replace the access cover (friction fits)

The first thing is to pop off the cover on top of the bonnet. If awkward a wooden cocktail sausage stick will do. The top cover comes off really easily. 



Remove the 21pin DC banking plate plugged into loco's PCB. Gently lever it off the 21pin connector using either a wooden stick of 4-5mm screwdriver blade. 


Try a wooden stick (ie ice cream stick cut to shape). Gently lever alternate sides up 1/2mm at a time until the plate pulls free.


If the wooden stick is not strong enough to get it to move use a 4-5mm wide small screwdriver blade. There is a screw head conveniently placed on the PCB under the corners of the blanking plate and you can rest one edge of the screwdriver on that rather than the surface of the PCB (ie to avoid accidental damage to the PCB). Use the screwdriver twisting it gently on alternate sides to leverage the plate up 1/2mm at a time each side of the 21pin connector. If done gently and gradually force is not needed.


The decoder should not cover the dip switches, see photo below, it goes towards the cab end fitting under the panel in front of the cab windows. There are wires in there so it won't fit initially until you nurse it into place easing it gently past the wires

Lighting wires make it awkward to slide the decoder under the body panel but with care its easy to fit.


Note the 21pin strip of pins has one missing on the loco PCB and the decoder is missing one hole, this is so that you align the decoder correctly. Be very careful to get this blank hole and missing pin aligned ok, it is very easy to bend pins if one hasn't go this right and force the decoder down. I find the locos pins will fit the decoder loosely giving you a clue its lined up ok before gentle finger pressure to push the decoder down allowing the pins up into the decoder holes.



Remember the decoders default address out of the box is 3 so when trying for the first time before you give the decoder its permanent address (eg 134 which is a LONG address btw). Note some DCC controllers treat the no 121 as a long address (Roco Z21), whereas others like NCE treat 121 as a short address.

Hope this helps. Noel

BTW, on one of my locos the speaker was perfect and sounded great, but on the other the speaker was faulty suffering severe distortion. MM are replaced the loco for me under warranty by return, excellent service.


PS: I've another thread somewhere showing how to get a driver into the 121 cab (requires a little lego, meccano skills and a screw driver).



Edited by Noel
More info plus extra photos
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