Farish 66 & six-wire decoder

QUOTE (Walter @ 29 May 2008, 16:47) <{POST_SNAPBACK}>Hi,

I have a Farish 66 and a spare six-wire, two-function Uhlenbrock 73400 dcc decoder from another project. Six wires, as there is no blue lead for the common function return. In a lot of N gauge models this runs via the chassis.

The Farish 66 has 7 solder tabs.

Would the two work together?? Could I just leave tab 7 (common function return) empty in the absence of a blue wire on the decoder, or is that not going to work with the lights?

Many thanks

Hi Walter,

I have just fitted a TCS M1 decoder to a Graham Farish freightliner/shanks loco following this link

http://smallphry.com/eecore/index.php/site...dcc_conversion/

click on the images for a better view of them, i did line the inside area where the motor tabs are with kapton tape and underneath the solder points on the chassis as a precaution.
As to the blue wire as far as i know it is the common positive for lighting, and its omission will leave the lights useless.

upnick.

QUOTE (Walter @ 29 May 2008, 16:47) <{POST_SNAPBACK}>I have a Farish 66 and a spare six-wire, two-function Uhlenbrock 73400 dcc decoder from another project. Six wires, as there is no blue lead for the common function return. In a lot of N gauge models this runs via the chassis.

The Farish 66 has 7 solder tabs. Would the two work together?? Could I just leave tab 7 (common function return) empty in the absence of a blue wire on the decoder, or is that not going to work with the lights?
Hello Walter,

You just need to make sure that tab 7 is connected to either of the track pick ups, and the decoder will do the rest I believe, i.e. decide if DCC signal is positive or negative and set the voltage to the LEDs or bulbs as appropriate.

It does this all the time anyway - if you pick up a locomotive and put it on the track the other way round then the red wire becomes the black wire etc. etc. and the decoder is clever enough to cope. It should be the same for the lighting - i.e. the common return is positive or negative depending upon the wiring and locomotive orientation...

QUOTE (goedel @ 29 May 2008, 20:49) <{POST_SNAPBACK}>Hello Walter,

You just need to make sure that tab 7 is connected to either of the track pick ups, and the decoder will do the rest I believe, i.e. decide if DCC signal is positive or negative and set the voltage to the LEDs or bulbs as appropriate.

It does this all the time anyway - if you pick up a locomotive and put it on the track the other way round then the red wire becomes the black wire etc. etc. and the decoder is clever enough to cope. It should be the same for the lighting - i.e. the common return is positive or negative depending upon the wiring and locomotive orientation...

I do not think that this is right (I say so with some hesitation, since I am by no means the ultimate expert on the subject). If Pin 7 is for the blue wire, which is normally the positive output for the lights, then there is no point in connecting anything to it, because 6 pin decoders do not have a blue wire and therefore there will be no output from the decoder. What you have to do is make a connection between either the red or the black wire and the side of the bulbs normally connected to the blue wire; this forms the path for the lights current. The DCC current does not change polarity according to loco direction, that is what happens with analogue DC control. The DCC current is more akin to AC. The supply to the lights passes only during one of the 2 phases of the current and the result is that the lights are dimmer than with the use of a blue wire as the current is less.

If you ever want to run the loco on a DC layout, it is best to connect one bulb to the red wire and the other to the black. This ensures that the lights change according to direction.

Hi Walter
I have done quite a few conversions of Fleischmann Locomotives. The 6 wire decoders use 1/2 wave power from the track as a power supply to the accessories . The conversions I have done , the loco's originally powered the Lights from the -ve side of the track (Black wire for DCC) The motor quite often needs to isolated from the -ve side of the track also.
I think it may be best to not connect tab 7 of your loco as your decoder may power the accessories (function wires ) internaly
and you may create a short between the decoder and the track. Better to be safe than sorry ! I converted one Loco with a NEM651 socket to DCC using a TCS T1 and it works Properly on DCC . The NEM651 is a 6 wire connection there was no Blue wire to power the functions.The black wire is used as power to the functions, so if no joy from not connecting tab 7 ,connect it to the black wire.Hope this helps
Zmil Downunder