Wiring Nightmares Can Come True

Wiring is not my favorite aspect of this hobby.  I love the look of bright locomotive headlights and the control available through DCC, and yet despite having enjoyed three years of high school electronics I just don't care for the tasks of cutting and stripping and soldering tiny wires.  I suspect it has to do with the unknown unknowns, that is, I don't know what might go wrong especially since half the time I'm doing something unorthodox.  

These days decoders and LEDs are drop-in or plug-and-play and that's fine for many modern locomotives.  However, vintage 1950 Mantua locomotives are a different matter altogether and adding DCC to such a critter requires ingenuity and creativity, math and formulas and even arcane knowledge.  Perhaps even live animal sacrifice, but I haven't quite reached that level of desperation....yet.

First off, here's what went well.  I managed to get 6 wires prepped and soldered to SIPP sockets.  Next I mounted these under the tender floor, feeding the wires up into the tender through the recently enlarged holes.  At this point I decided I'd hook up the rear light and see how that looked.  I did the calculations to determine the correct resistor value, soldered the resistor to the yellow wire and soldered this to one wire of the light.  I soldered the other wire from the light to the common blue wire pad in the tender.  So far so good. 

Then I switched on the power.

The bulb began to flicker.  Not blink - I know that's a fail safe warning that there's a short somewhere - but flicker randomly like a candle.

I didn't get a picture of the flickering bulb.  Enjoy this lovely image of the moon at sunset instead.

I made sure I had dialed in the loco address, had it in reverse, and had the light on.  Still flickering.  I could turn it off with F0, the lighting function, but whenever I'd turn it back on it would flicker.  I tried adjusting the CVs in case somehow from the factory it came set with that option but no, so I eventually just reset the decoder using CV8.  Now the light wouldn't come on at all.  Well, crap. 

I wondered if somehow I had miscalculated the resistor value, so I once again stuck my meter leads on the blue and white wires.  Huh...now I have 13.4 volts...when the F0 is OFF, and 7.3 volts when it is ON.  I had calculated the resistor value based on 13.4.  Maybe that was too much?  No, the bulb flickered, and a reading of 13.4 would make sense based on typical AC track voltage brought down to DC by the decoder.

I baked this apple pie for Thanksgiving with fruit from our front yard.  My first lattice top, made with Gluten Free crust!  Much nicer to look at than nasty old wiring and a troublesome decoder.

SO, Next I set up a test bulb on a beadboard with a 220 ohm resistor for safety, assuming the 7.3 volts might be right, but also hedging my bets that the 13.4 might be right.  Could blow the bulb but not likely.  This proved my fears.  The bulb burned brightly on the blue and white wires (forward headlight function), but only when the F0 was OFF.

The rear light was still not even glowing unless I caused a short between the blue and white wires...and then only for a brief moment.  Rolling the tender seemed to stop it.  Then the forward test bulb came on when F0 was ON, but dimly, and was bright again when F0 was OFF.

By now I my head was well and truly spinning. 

This is my Mom's kitten, Claire, sitting with our dog Ellie.  They're friends.

Seeking advice online only resulted in more confusion.  I'm pretty convinced the decoder isn't working as it should unless I'm missing something.  It IS 20 years old, at least, though it was never used in that time except to hook it up to the tender.  I probably blew it somehow or I got a lemon, either way, I'm done messing with it.  It has been removed and will be relegated to the someday-maybe bin in the electronics box.  Who knows, the motor control might still work, in which case it could be used for an animation element.

I have ordered a TCS KAM4 LED - that is Train Control Systems' Keep-Alive Mobile 4 decoder set up for LEDs without having to use any additional resistors.  I'm going to modify my solder pad to have 8 individual pads instead of 4...I mean, what was I thinking 20 years ago?  Why not just cut another groove and solder ALL the wires to the pad instead of bundling some with heat-shrink tubing?  Anyway, in the mean time I'm going to continue my adventures in electronics by installing the locomotive half of things, including a two-pin connector for the front light so I can separate the shell without breaking tiny wires.

Updates as they happen.  Thanks for reading.