Dave,
After I reassembled the locomotive, I ran it for abourt 5 minutes, and it ran fine. I think it is too soon to tell- but I remain optimistic. In the past, sometime it would run fine for a while and then stop,other times, it would hardly run at all. I would take it apart, move some wires around, and try it again....w will see.
Thanks for asking,
Mr. Mick
MrMick:
Glad you got the LED fixed.
Did you solve the original problem with the locomotive shorting out after running for a while?
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
After checking the voltage from the decoder upstream and downstream of the resistor ( 10v and around 3 v)(OBTW,that also told me which lead was '+'), I concluded that the LED was in fact fried; I nipped it out, soldered in a replacement, and it worked fine; Thanks for all the tips and suggestions,they were very helpful to me as I worked through this problem.
I use two AA batteries wired in series with a pair of test probes. I use this for testing white LEDs - no resistor required.
Before removing your LED from your engine, disconnect the wires from the decoder and test the LED to make sure it is in fact not working. It is rather unusual for an LED itself to go bad. If it has, it's quite often caused by something other than the LED itself (shorted wire, etc.).
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
With the voltages you are working at <18V if you install the lead backwards, it simply won't light. However on most LEDs there's a small marking or notch, or longer leg to indicate the positive leg. If you are unsure test it with a resistor first.
And use a volt meter to determine if it's the LED and not the decoder wires that are broken. It's rare for LEDs to burn out UNLESS you put too much current into them. (>30ma typically)
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Thanks for all the help: step one, re-examine the connections of the currently installed LED! That chart looks like a keeper,also!
Ed:
Great chart!
Thanks
An LED failing is kind of rare. A nine volt battery and 1k resistor is an easy way to check.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
You won't hurt the LED with reverse polarity but I don't understand why there would be a question about the orientation.
You can check the polarity of the current supplied from the decoder with any volt meter set to DC volts. An analog meter the needle will try to go below 0 if you are backwards, a digital will show minus volts if you have the red/black probes reversed.
You can see how the cathode marking is on the SMD by looking here:
https://www.google.com/search?q=surface+mount+led&biw=1366&bih=681&tbm=isch&tbo=u&source=univ&sa=X&sqi=2&ved=0CFoQsARqFQoTCKTwoPqaoMgCFQgdPgodyFkHVA#tbm=isch&q=surface+mount+led+cathode+marking
Good Luck, Ed
On the back of the LED there will be a polarity symbol. It is usually a green 'T' or triangle. In the case of the T the top of the T is positive. In the case of the triangle the 'point', or top of the triangle as it were, points towards negative.
It isn't difficult to test the LEDs for polarity. All you need is a 12 volt power supply, some test leads and a 1000 ohm resistor. You will have to determine which lead is positive on the power supply. Connect the resistor in line with one of the leads and touch the solder tabs on the LED. If it lights, the positive lead is on the positive tab. If it doesn't light, reverse the leads. That will have the added benefit of proving the LED actually works. This setup is also good if you want to tone down the brightness because you can insert different values of resistors until you get the amount of light you want.
If you install the LED backwards you won't harm it assuming it is only getting normal operating voltage.
One thing I would point out is that LEDs don't often fail under normal operation. For that reason I would take a close look at all the connections before ripping it out.
I have only installed a few LEDs but I would guess that most of them were backwards on first try. They all survived and are still working. YMMV.
Several years ago I installed a couple of 603SM LEDs into an RS3 for headlights when I converted it to DCC. So while I was troubleshooting the loco recently, as it was acting like it was shorting out after being in operation for a while, one of the LEDs stopped working. I am going to replace it; however, I do not know the polarity of the led that is installed - just replacing it gives me a 50% chance of getting it right - if I guess wrong, will the reverse installation burn out the LED?