Large scale 3 truck Shay wiring

[thelenster]

I'm preparing to install a decoder in my Shay. There is a pair of blue wires tied together and going nowhere?? No indication from the supplied wiring diagram as to where they go or what function.
Len Jaskiewicz

[Tony Walsham]

The blue wires are connected to the mechanical chuff timer in the Shay cylinder heads.
They provide three beats per shaft revolution.

[thelenster]

Thanks Tony.
Now I'm perplexed as to where the ground of the decoder gets wired to the Shay board? Bachmann should supply schematics!

[richg]

Thanks Tony.
Now I'm perplexed as to where the ground of the decoder gets wired to the Shay board? Bachmann should supply schematics!

Not sure why you are asking about the ground. There is actually no ground in a decoder. There is a common for the wiring which is the minus side of the full wave bridge rectifier and the minus side of the first filter capacitor for the bridge rectifier. I find those points when poking in a decoder with the Scope.
Bachmann figures, if you are going to dig into a decoder, you know electronic circuits.
There is no common or ground for the DCC signal.

What does confuse some is the blue positive wire is labeled common but is common only for the lighting circuits.

Below is a basic diagram of a DCC decoder. Just ignore the cap, diode and reistor.



Rich

[richg]

Something important with Bachmann DCC, they do not always use the NMRA color wires for installations. Another reason to know electronics and how to use a multimeter to trace the wires.
Don't waste time with a Rant. They will change this procedure eventually, maybe.

Rich

[thelenster]

Thanks All,
It's not the decoder that I'm questioning but the locomotive interface board. With the newer plug'n play models the DC dummy board or supplied interface board have a clearly marked GND connection. I did run across a well done schematic of the K27 board/ function connections etc. wired to a decoder and it sheds very good light! I'll have to trace out the Shay, as it has 6 screw terminals but no indication of what is what.

Regards,
Len