Rail Truck Headlights

[ceverest]

I have installed a Soundtraxx decoder in the rail truck and everything is working fine except I am having an issue with the headlights. I am fairly sure they were working prior to removing the original PCB. Are they LEDs as most of the descriptions of the rail truck seem to indicate? The rear LED works fine but I can't get the headlights to light up with a multimeter tester or when applying 3.3VDC.

[2foot6]

They are LED's,have you tried reversing the polarity?.The wires are very fine ,you may have a broken wire near the decoder or the decoder may need programming.

[ceverest]

I have tried powering them up with a power supply at at 3.3v and with my multimeter in diode mode and I get nothing. I get a resistance reading of about 188 ohms with either polarity which is a little strange as I don't get a resistance reading with other LEDs I have.

[2foot6]

was the decoder hard wired or plugged in?

[ceverest]

The decoder is hardwired but the headlights are not connected at the moment. I was trying to determine polarity and see if the headlights are working. Like I said before I have tried to power them up with a 3.3V power supply and a multimeter with no success. I did have them wired to the decoder with inline 1K resistors but have disconnected them until I can find out what's going on.

[dutchbuilder]

Did you measure the led's when disconnected  or connected to the pcb?
Always see if the led's work individually using the multimeter.
Using a power supply without any resistor can damage the led.
Voltage is not important, Current is much more.
If the led drawes more than is allowed (20mA) you will damage the led.
R=(U-U led)/0.02

Ton

[ceverest]

Disconnected and tested individually with multimeter. Don't understand why I am seeing the 188 Ohm resistance with either polarity.

[dutchbuilder]

If i want to see if a led lights up i use the beeper/200 Ohm function.
If i want to test the diode working of the led i use the diode/2K function.
Your 188 Ohm is a mystery to me.

Ton

[ceverest]

Tried testing both ways with no success. I'm only getting the 188 Ohm reading on one LED. It's possible both of the LEDs are fried I just don't know how that would have happened.

[dutchbuilder]

Looks like it.
The only way i can imagine is to much Amps.

Ton

[2foot6]

Did you have a limiting resistor in series with the LED.s?..The decoder probably would  have 12 volts  available for lights,too much without the resistor.

[ceverest]

If you read one of my earlier replies when I first installed the decoder all of the LEDs had 1K resistors attached. The multimeter and power supply testing was done without the resistors. If I have managed to toast the LEDs and because replacements are out of stock at the Bachmann store what can someone recommend for replacement LEDs? I have looked a several sites and Evans Designs (https://www.modeltrainsoftware.com/collections/hobby-leds/products/chip-nano-pico-leds?variant=6807584833584) pico or nano LEDs might be suitable. Any other sources?