What LED diode type needed to fix??

[Serge125]

Hi all!!

Ok trying to fix a Christmas light house that has 2 5mm cool white led diodes and one is dead so how can I determine what type of led that I need to replace it, there isn't any markings on the led to know what you need. I know they are both 5mm and I just replaced them with leds that I had but they don't light up and they were both working before I installed them so how can I find the right led to replace the one that is burnt??? There is a very little circuit board that has a cap and resistor, the power input is 12v ac (that powers the spinning motor and yes it's AC) and supply the voltage to the circuit board that has a 47uf 25v cap and a 390 ohms resistor that powers the leds. Thanks for any information regarding this little problem!!

UPDATE; Ok did some measurements with my meter on both leds (the one org and the one that I'm replacing) and on the org one the diode test I get no V reading but it lights up (of course) the one I'm replacing I get a reading of 1.8v AND lights up too but it's not white it's a yellowish/green colour. So right there I know that these are two different diode type so what is what so that I can get a replacement?

THANKS in ADVANCE!!!!

Serge

[807]

Are you sure your replacement LED is a white one? White LED's generally drop more voltage across them (around 3.4v I believe) than coloured ones.

As there is no rectification, the LED's might be connected in inverse parallel, so each one lights up alternately on the direction of the ac.

Could you follow the wiring of the circuit in order to draw it out?

[Swake]

Your meter (I assume it is a multimeter) is likely to output about 2V in the diode check mode. That is enough to faintly light up a white or blue LED, but as the LED needs about 3 volts the meter cannot measure it. The multimeter will be able to measure a red, yellow, orange or green LED as these only require about 1.8V.

LEDs have a polarity. As explained by 807 and based on your description, the 2 LEDs are likely wired in inverse-parallel. Also this is something you have to consider when testing the LED with the multimeter. The LED should light up in one way but will not light up when the test leads of the meter are reversed.

You can replace a broken white LED by another white LED or a blue one. About any 5mm white or blue LED will do. It is likely that the originals are high intensity LED's. Due to the voltage difference it is generally not possible to replace a white LED by a yellow, orange or red LED unless the resistor is adapted to reduce the voltage over the LED.