Digitrax DZ123 - need headlight help

[mediaprof]

I'm having trouble with the headlight in a Bachmann On30 2-6-0 locomotive using a Digitrax DZ123 decoder. I installed the decoder about five years ago, and it worked perfectly until last summer, when the headlight suddenly stopped working. I suspected either the fault was either in the lamp or the connections. Here's what I've done so far:

• When I separated the loco shell from the chassis, the lamp worked briefly, but then quit.
• The lamp functions normally when connected to either DCC track power or a 9 volt battery.
• Suspecting a loose or cold solder joint, I unsoldered and resoldered both leads to the lamp.  No change.
• I reset the decoder to factory default using CV 8 set to value 08. No change.

FYI, I'm running an NCE DCC system.

I'm beginning to suspect the fault is in the decoder. Any comments or suggestions appreciated.  Thanks.  

 

[rrinker]

 Is this an actual incandescent lamp or an LED? If it's an incandescent lamp, then I would also suspect the function output on the decoder had failed. An incandescent bub, even one rated for the full track voltage, thus typically not needing any resistor, has an inrush current which can easily excced the limit per function on the decoder. It's only a brief inrush, so it works fine for a long time, but eventually those small spikes of overcurrent can take their toll on the decoder.  Easy enough to test, measure the voltage between the blue )+) and white (-) wires with F0 turned on. If you're t getting somewhere around 12V, the function is probably blown. If there's no backup light on the loco, try the yellow wire, which is F0R, you can program it to be active in forward instead of reverse, or active in either direction.

                          --Randy

[mediaprof]

Thanks Randy.  This makes perfect sense, and conforms with the evidence, so I'm sure you're correct.  I happened to be near my DCC-friendly hobby shop this morning, so I picked up a new decoder.  Case closed.