There are only two wires going to the LED. One is the positive, the other is the ground. Find the positive wire, cut it and run a wire from the LED.to the Right rail wire and use a resistor (1K) between the LED and the right rail. Now it will be bright and you can control it>
Bob, call Athearn Customer Support and tell them the problem. If the function output supply is only 1.5 volts, they can suggest a workaround since an SMD needs to be resistored on a 12 volt power supply to work. You want to use the function output, not track power, so you can control the lighting effects.
Rich
I have given the OP the quick and easy way to get this working. He will have control of the H/L just like I have stated. Taping the right rail will give you 1/2 wave A/C volts and the control wire is still on the original board. Try it! It works!!! The installer of over 1000 installs.
If he bypasses the function output for the headlight by tapping into the rail pickup, how can he control the headlight (e.g., off in reverse, dim under Rule 17, etc.)?
Rich
The control comes from the negitave side not the power side.
The function wire completes the curcit.
Trust me, I have done many just like I said.
They work just fine!
Well, what the heck, it can’t hurt as long as he adds the appropriate resistor to the SMD. Give it a try.
Rich
I tested the voltage on the light socket at the board and it is 1.55 volts. The socket has four pins but only two are installed in the plug; the outside ones the get the 1.55 volts. The inner ones read about 5.6 to 6.0 volts. I couldn’t seem to find any other points on the board to connect to? I never found a 12 volt reading at any of the connection points. I will try this method suggested by woodone and see what happens. I do want to maintain function control of the lights. Also may call Athearn and see if anyone there has a solution.
-Bob
I found the PDF quite easily but I don’t think it will be much help. The decoder must have a dedicated 1.5 volt regulator.
http://www.modelrectifier.com/resources/dcc/0001821%20diesel%20Athearn%20F's.pdf
The 12 volts DC is easy to find. Right at the output of the full wave bridge rectifier. Just no control of the lights if you go that way.
Rich
Woodone has the answer … but apparently either nobody believes him or doesn’t want to try it ! [sigh]
Mark.
Issues like this can be confusing for those with limited electrical DCC experience. We shall see.
I would certainly try the suggestion.
Rich
I, for one, fall into that category. Once the OP solves his problem, and assuming that he reports back that the rail power suggestion worked, I hope that someone more knowledgeable than me will take the time to explain this in more detail.
I always thought that the wiring of loco lamps, headlight, rear light, ditch lights, were always dependent upon their assigned function outputs. For one thing, the function output voltage is typically lower than the track voltage, or so I thought. And, I always thought that using the correct function output tab was critical to the proper application of CV values for advanced performance of the lamps.
So, do you not even need to use the function output tabs as long as the other leg of the LED or incandescent is wired to the accompanying common tab for the designated function output tab?
Anxious to learn more about this whole topic, and anxious to hear if the woodone solution indeed works.
Rich
Rich, you posted a wiring diagram of an MRC decoder earier. If you look the way they show how to hook up the lights you will not that both lights show a common, THAT IS THE POWER TERMINAL. The other wires ( one to each bulb) is the control wire. The LED does not care where it get its power, but it must be enough ( about 3 volts) to make the LED light. With getting power from the rail you will be getting 1/2 wave form from the rail. If you read the voltage across both rails you should see about 14 volts. so 1/2 that is about 6 volts. YOU MUST USE A RESISTOR !!! 1K will work. you can use more if you want to dim it a bit.
That was richg1998
Rich
Sorry, But the diagram is a good example…
OK guys, I followed woodone’s advice and he was correct! The front headlight now functions as it should and goes off when in reverse and also using F0. I installed a SMD cemented to a short length of 1.5mm fiber optic rod and put it in the hole where the incandescent bulb was. It looks great and works great! Thanks to all who commented on this issue and especially to woodone. I was a little skeptical of this solution at first too, but now
This solution has been in the Digitrax literature for some time. See the latest Digitrax decoder manual: http://www.digitrax.com/static/apps/cms/media/documents/documentation/Decoder_Manual_V2-01_2014.pdf See page 22 for an illustration of options. Even though this is a Digitrax manual it holds for other brands of decoders as well as Woodone has shown.
Joe
So, you don’t need to use the function output tabs for the front and rear lights, just the common tabs?
Rich
It is, but only by about 1.5 volts, the voltage drop of the diode bridge rectifier.
They are. You don’t replace the function output lead (white, yellow, etc… on a wired decoder) with track power, you replace the common (blue) lead.
No you do need the function output, you don’t need the common.
It should not be a surprise that this works, it is actually a common way of wiring lights in Europen locos. Ever seen a 6 pin NEM 651 plug decoder or socket (this is what is used on Fox Valley Models diesels)? They only have 6 pins because they use the rail pickup for the function common.
Thanks for that clarification, CSX.
Incidentally, not being from Europe, it was a surprise. [(-D]
Rich
It’s like this (I’ve posted explanations on this several times - one more of those things I really need to just type up and post on my web site so I stop repeating myself): The function ‘outputs’ on a decoder are not ‘outputs’ - they are connections to ground. The various color wires, white, yellow, green, violet, etc. connect to switches that either are open (no current flows) or are closed (they connect to ground). The blue wire is really the