In a past post I was learning how the Athearn/Digitrax PC board set the power limits for head and rear light bulbs. After discussions here, and at our club, I learned that if I removed the eight limiting diodes and increased the 150 ohm resistors to 1K I could then attach LEDs to the head and rear light tabs. the project has been a very satisfying success.
Hello all,
Personally I would remove the PCB and use a Train Control Systems (TCS) KAM 4 LED decoder and hard wire it, rather than trying to modify the existing PCB.
You can find these decoders on eBay for around $50.00.
This decoder can be directly wired to LEDs without the use of resistors.
Because it is a four-function decoder it can power four lighting functions from head- and rear-lights to ditchlights, strobes and interior lighting.
Hope this helps.
"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"
Frankly, I ALWAYS rip out the factory boards. Little point in keepingm it or attempting to modify it when there are direct drop in replacement decoders that even sit on the same mounting tabs that hold the board tot he chassis. Even if I don't use a board replacement decoder - the crazy wiring I've seen on some factory boards makes it not wortht he effort. My locos are pretty simple - I model an era way before ditch lights, so I have a total of 8 wires to hook up - 2 track inputer, 2 motor wires, a front light, and a rear light. It's easier and faster for me to just wire it up directly, plus I know it will work (unless I idiotically wired one of the LEDs backwards - haven't done that one for a while). Factory boards, especially ones from early in the DCC days, require traces to be cut or other such nonsense. And in the case of some brands, mostly Bachmann, contain filter capacitors that interfere with the operation of a good decoder.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Capt. Brigg, That is a clever modification that makes perfect sense. Thank you for sharing this with us.
First, I don't think this board comes factory installed, at least not on any of my older bluebox Athearn engines. They can be purchased from Athearn for about $15 and make installing a decoder very easy. I use an NCE decoder that can also power ditch lights and/or beacons directly off the board.
Secondly, I have been given several of these PC snap on boards by other members of our Willamette club because they did not know how to use LEDs with them. I am hoping, by making this information available, other modelers with this board will be able to simply modify the board for LED lighting.
No, those only come on newer RTR locos. It's in a way a replacement for the no longer available (because the clip is no loonger sold seperately, or at least Athearn won;t sell them to Digitrax) Athearn harness that Digitrax made.
I do wish Athearn would join the 21st century and stop making everything for incandescent bulbs. It wouldn't have been too difficult (and cheaper) to make that board as a universal device to which the modeler could install whatever resistor needed for either LEDs or bulbs. Modeler's choice, not forced on by Athearn.
To use that board on an older BB loco, you still have to insulate the bottom of the motor from the chassis. The only hard part about doing a BB loco without a board is getting the chassis side power pickup - you can't solder to the frame directly. A small hole and a self tapping brass screw makes it easy.
ANd you somewhat illustrate my case for just hard wiring decoders - you had to sit down and trace out the circuit on that board to figure out that you have to bypass the diodes and change the resistor. Next different brand loco - back to the drawing board. I did that on some of the first locos I converted which is what drove me to the "this is nuts" stage. They aren't all as straightforward as this Athearn board. The one that finally made me switch exclusively was a P2K something or other, one of those "cut at the X for DCC" types. I traced out the circuit and half the stuff on the board was no longer used once the traces were cut. Including one of the resistors - on DC it used a seperate resistor for the front and rear light, on DCC it ended up using just one of them, pretty sure on the blue wire. In some cases I've retained a bit of the board as a mounting point - Walthers FA is a good example. The board fits in a slot at the front and has a screw hole at the rear. I chopped off all but an inch or two of the board and screwed it back to the chassis mounting hole, and used that as a place to tape the decoder to keep it out of the drive bits.
BTW when I say hard wire a decoder - the ones I use all have a 9 pin or some sort of plug at the decoder end, so should i ever need to, the decoder can be popped out and replaced without unsoldering anything. And the 9 pin connector is a standard, so I can swap brands if I want to.
Thanks for the tip Capt Brigg!