Model Railroading > LED headlight flashing like a strobe - cause?

I have an Atlas C420 I bought from a friend with the Tsunami, flasher, and LEDs already installed, and with almost no run time.  Worked fine at first, but the front headlight started flickering after about 15-20 minutes of operation - not like there was dirty track, but more like a constant, fast strobe effect.  Sound never cut out, the motor never hesitated, other units in the consist were fine, and the flashing continued even when sitting still, so I'm confident that it's not a track issue.  After that first occurrence, it would start flashing from the moment I turned the headlight on after resting for several days, with the same intensity/frequency.

In attempting to troubleshoot it, I tried moving the front LED and resistor to the rear headlight pads.  Same strobing problem there, so I was fairly confident it's not the decoder.  I swapped the LED/resistor combo from the rear headlight of this unit to the front, and everything was fine.

Has anyone else ever experienced this?  This unit and its sister Alco, an Atlas RS36, are the only ones on my roster without either open (Cannon) fans or an open etched radiator, so one theory is that perhaps the decoder overheated and somehow damaged the LED or resistor, even though the unit was never running hard.  My layout has a 25mph speed limit, short trains (15-18 cars), and no significant grades, and this unit was running with two other powered Atlas/Kato units.  This consist had only made 1-2 laps of the layout for an open house - probably 250' max - so overheating doesn't seem likely to me.  IF that's the case, though, I'd like to resolve it before repeating the problem.

Do Tsunami capacitors get hot?  Due to space considerations, I normally mount mine in the cab simply using wire tension to suspend them in mid-air, but I just realized that in this installation, the capacitor is resting directly on top of the decoder.  Could that be a problem, and could it have led to the LED or resistor going bad?

I'd appreciate any guidance on this issue.

Joe Atkinson
Council Bluffs, IA
www.iaisrailfans.org/../Sub4WestEnd



Edited 2 time(s). Last edit at 06/30/15 10:27 by iaisfan.

There are leds with flashing circuits built into them. If you disconnect the problem led and hook it to a couple of AA batteries do you get a steady light?

Posted from Windows Phone OS 7

fbe Wrote:
> There are leds with flashing circuits built into them. If you disconnect the problem led and hook it to a couple of AA batteries do you get a steady light?

To clarify, this LED was actually shining steadily when I first acquired the model.  The "strobe" problem only began after running for 15-20 minutes.

Just for fun, though, I tried your suggestion, and it doesn't light at all.  Just a bad LED perhaps?

 

Joe Atkinson
Council Bluffs, IA
www.iaisrailfans.org/../Sub4WestEnd

LEDs are polarity specific so did you try it both ways? Was the resistor out of the circuit with the batteries?

Yes, leds do go bad but I hate to toss one out if I just got one part of the test process out of wack. I'm rooting for you.

Posted from Windows Phone OS 7

Joe, is it the same flash rate you see if you have two throttles assigned to one loco address?   If you have JMRI and a test track, does it do it on the programming track?

fbe Wrote:
> LEDs are polarity specific so did you try it both ways? Was the resistor out of the circuit with the batteries?

I tried it both ways, and both with and without the resistor.

> Yes, leds do go bad but I hate to toss one out if I just got one part of the test process out of wack. I'm rooting for you.

Thank you sir!  I appreciate all your help.

> Joe, is it the same flash rate you see if you have two throttles assigned to one loco address?

Ummm...not sure.  Lenz doesn't make the headlight flash if two throttles acquire the same locomotive.  It just gives control to the later throttle, and causes the locomotive number on the first throttle to flash.

The rate at which the C420's headlight was flashing was something akin to what you might see behind John Travolta in "Saturday Night Fever". :-)

> If you have JMRI and a test track, does it do it on the programming track?

Sorry, no JMRI here.  With Lenz, I'm not aware of a way to attempt to activate the headlights on the programming track.

Joe Atkinson
Council Bluffs, IA
www.iaisrailfans.org/../Sub4WestEnd

If you swapped it to the rear and got the same thing, my guess is that it's probably the LED.  There's probably something shonky inside of it, and once it heats up, it starts acting like a weird blinker.  I've seen some weird failure modes in LEDs, but I have to admit, I've never had one cycle that quickly.  I've had one cycle a couple times a second from a bad bond cycling thermally, but never go disco fast on me.

Thanks Nathan!  So far, so good with the new LED.

Joe Atkinson
Council Bluffs, IA
www.iaisrailfans.org/../Sub4WestEnd