# Bachmann 3 truck Shay decoder installation



## thelenster (Feb 18, 2012)

I'm installing my first decoder into a G scale Shay that is DCC ready. Documentation is terrible. I don't see where the decoder ground is to be connected?? Any help appreciated. Looking at the circuit board it does look lige what coulb be the ground going to J3 and there is a white wire looped to that terminal?
Len Jaskiewicz


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## ntpntpntp (Jan 14, 2008)

Which decoder are you installing? 

I don't recall ever needing to connect decoder ground in any of my large scale loco installs so far (including a QSI into a Bachmann 3 truck shay). Referring to the Bachmann DCC diagram and it's wiring connection table, all you need to hook up are the track and motor feeds (orange/red/grey/black), and from the 6 way connector block you need the function common + (blue), the white and yellow (lights), the brown if you want control of cab light and smoke via a DCC function (I didn't bother with this on my QSI), and the speaker wires if it's a sound decoder.


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## Greg Elmassian (Jan 3, 2008)

Most decoders don't have a "ground", most only offer the "common" for the lighting and function outputs, which, by the way is positive voltage not ground or negative. 

Please tell us what decoder you are using. 

Greg


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## thelenster (Feb 18, 2012)

I'm installing Zimo MX695 and MX690 decoders. With the newer Bachmann DCC ready that have the plug in board there is a GND wire, so no questions asked there! The decoder has a common V+ that serves the functions, lights, and a GND, so a return path is needed. Without schematics to decipher proper wiring, this does get a bit frustrating to me. 
Len Jaskiewicz


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## Greg Elmassian (Jan 3, 2008)

Does it look like page 14 of this document?


*http://www.bachmanntrain...trong>*


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## High Ball John (Jan 26, 2009)

Both Massoth and Lenz decoders have a GND pin, some others would describe this as Decoder-. The LGB DCC Interface has a GND pin, and I beleive some of there other interfaces use the name GBD too. Sorry don't know much about Zimo or Bachmann installs.


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## ntpntpntp (Jan 14, 2008)

TheLenster, have you tried it anyway without worrying about the GND connection? As Greg has said, DCC function connections work as the negative or ground path with the function common as the positive side. I don't think you'll need the GND connection.


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## ntpntpntp (Jan 14, 2008)

... The only time I've seen decoder GND used is with a power buffer (although no doubt there are other uses)


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## Dan Pierce (Jan 2, 2008)

The Zimo decoder does have ground pins and these are used for the reed switch inputs for chuff, bell, whistle. 

Also used for servos as you need ground, 5 volts and the signal pin. 

Zimo MX695 also has a ground and power pin connection for using super caps for dirty track. This can be a 10,000 uf 25 wvdc or 10F caps in series for 17 volt operation. 

So, in the MX695 there is V+, and 10 volts in all models, and some models have additional 5 volts and an adjustable voltage. 

Function outputs just supply a ground via a mosfet. 

However you do not hook this ground up to other boards that have track power on them as you can get instant magic smoke!!!! But why with a full decoder like this would you have another board tied to track power????? 

When I do a Bachmann engine, I remove the electronics and just use the decoder to control everything.


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## thelenster (Feb 18, 2012)

I am going according to the K27 schematic I found at this site.

http://1stclass.mylargescale.com/stevec/Misc-Files/K27dwg-01.jpg 2/18/2012

The schematic is very clear as to the grounding of the interface board and the decoder! Going by this schematic and continuity comparison on the shay interface the terminal marked J3-6 is the common GND. I'm just following my 30+ years of EE power supply experience! 

Happy New Year,
Len


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## thelenster (Feb 18, 2012)

Thanks Dan, 
You might be right in this case as opposed to the newer plun'n play boards. Letting out the 'magic smoke' is not a good thing! Accurate schematics are a good thing to verify proper operation, etc. 

Len


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## TonyWalsham (Jan 2, 2008)

The 3 x truck Shay pcb terminal J3-6 is indeed connected to the pcb ground. I verified that by continuity checking between the terminal and the voltage regulator tab. 
There was also a white wire connected to J3-6. I do not know where that is connected to.


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## Greg Elmassian (Jan 3, 2008)

Do not connect the K27 ground to the Decoder ground... remember that the decoder basically has it's own power supply it's derived from the rails, but the Zimo ground may not be at the same potential as the K27 board ground. 

Ever hear of a "ground loop problem" ? With 30+ years of experience you most certainly must have, especially in power supply design! 

Greg


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## Greg Elmassian (Jan 3, 2008)

Any progress? 

Greg


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## thelenster (Feb 18, 2012)

I've sucessfully installed the Zimo MX695KV into my first Bachmann Mallet. Sound loaded is Dappen logging Mallet. The grounds have been connected with no smoke! Removing the Bachmann interface board would be a disaster as there is a free running oscillator for the firebox flicker and other functions. Bachmann has done a good engineering job with this latest plug 'n play board compared to previous DCC ready models.
The Zimo performance with stock CV setting is smooth, and the sound is absolutely. awesome!


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## thelenster (Feb 18, 2012)

*Special note for the Shay! *My first installation of the Zimo decoder yielded all sorts of intermittent results. As it turns out, all the wires going to the main interface board are extremely succeptible to break, especially if they have some strands that have been cut. They were breaking like crazy.34 wires in all!







Good thing I had a second untouched Shay to follow the wires. Now I've numbered all the wires and installed robust connectors wit strain relief and all is well! This is also a benefit when it comes to weathering as the whole assembly can be removed. 
The Zimo decoder with the new Dappen Shay sound is incredible!!


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