I have an Atlas Master series GP40 with the dual mode #342 decoder. Works a treat and is a superb locomotive. I wanted to add some ditch lights, but before that I tried researching about the decoder and found there are function C & D outputs for exactly that purpose.
To test these I first clipped on some LED's (with 1K resistors) and set the necessary CV's. They worked fine. I really wanted to use some grain of wheat lamps I had so I next clipped on some 12v mini lamps directly. Things worked great for a few minutes before one lamp stopped working, after another minute or so the other stopped. I removed the lamps and checked them out with a battery and they were fine so the problem seemed to be on the decoder. I went back to the LED's and they worked but were very dim now. I checked the voltage out of the C&D pins and I seem to be only getting around 2v.
I'm just going to take a stab in the dark on this one .... the function outputs on the 342 decoder are rated at 150 milli-amps. Depending on the 12 volts bulbs you were testing with, there's a posibility they were drawing to much current and stressed the output transistor.
Most miniature bulbs for model railroad use are usually any where from 15 to 85 milli-amps, so if that's what you used, that shouldn't have caused any trouble.
You could set your power-pack to 12 volts and put your meter in series with the bulb to see what kind of current it draws out of curiosity (if you don't already know).
Another strange thought .... when you "clipped" the bulbs to the board, the clips didn't short out a circuit trace on the bottom of the board maybe ?
Thanks for the reply. I am pretty sure I did not short anything out, as these are plastic similar to the ones on the other function out pins. The lamps are rated 12v 60mA. In conjunction with the function A or B lamp being on I guess there might be a case for exceeding the 150mA the manual says is the limit.
A plastic sleeve might describe it better. The wires are connected fine. I know how to wire things up and have built smaller circuits around the layout for various things.
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Posted - 03/12/2009 : 21:16:07
