Here we go again (another decoder problem)


IronBeltKen

IronBeltKen

Lazy Daydreamer
Lately I seem to be spending more time doing electrical repair work than running trains. Now another one of my locos is failing.

The headlight on my Atlas GP38 has stopped working. I don't know if its because of the LED being burned-out or the decoder itself being bad (the motor and sound controls are working fine). Is it common for LEDs to burn out the way filament bulbs do, or do I need to buy a new decoder? It's a SounTraxx AT100 LC series 1st generation decoder (reputed to be junk, but mine has worked for ~4 years).
 
Test for voltage output from the decoder leading to the lights/LEDs. If you see any voltage, and not something ridiculously high for an LED that isn't protected by a resistor, then your LED might be hooped. I don't know about resistors, but if it fails and allows excessive voltage to get to your LED, that would mean two replacements.
 
Ken, as Crandell said, check the outputs of the decoder with a meter. Sounds like the LED maybe cooked. This will happen if the resistor to it fails.

If it is the decoder, aren't there some auxiliary lighting outputs than can be tapped to use as the headlight on the Tsunami's? I'm not sure because I don't own but one, and I don't use the headlight outputs on it at all. Steam engines in my part of the country never ran their headlights in the daytime.
 
Ken
Put it in a shoebox and bring it up here will ya?:D
Yes, it could be a fried LED, or a poor connection, or a loopy decoder which may just need some CV's reset or another function can be tapped and reset to the headlight.:confused:
We got soldering station, lighting, magnification, DVOMs, LED's, resistors, NCE PHP and JMRI, me casa, su casa :)
 
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First, check to see what the resistor value is. If the resistor doesn't have enough resistance to compensate for a power surge, then your LED may have blown. The other thing is, LEDs don't last forever, so you may have just reached the end of the life of that LED.

When I install lighting for my locos, I use 16 volts when I calculate the resistor value. This is because there is a section of the club layout that puts out 15.4 volts instead of the standard 14. This gives me a safe resistor value to use, and if there is a power surge or spike, it won't blow out the headlights if they are on.
 
Well, I believe you guys nailed it: There is 13.5v being applied to the LED.

I can't remember how to interpret the different colored stripes on the resistor, but it reads ~267 Ohms on the meter.

Regardless, this means the problem is not with the decoder, but the LED and/or resistor - right?

Karl - sure, I can drop by - as long as I know what time(s) you'll be there...
 
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