LED diode type needed to fix??

[Serge 125]

Hi all!!

Ok trying to fix a Christmas light house that has 2 5mm 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!!

THANKS in ADVANCE!!!!

Serge

 

[Serge 125]

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 reading but it lights up (of course) the one I'm replacing I get a reading of 1.8v AND lights up too. So right there I know that these are two different diode type so what is what so that I can get a replacement?

 

[Diver300]

The original LED assembly could be two or three diodes in series.

1.8 V is a typical voltage for a red LED.

 

[Serge 125]

The original LED assembly could be two or three diodes in series.

1.8 V is a typical voltage for a red LED.

Hi and thanks for your response.

I know that the one I have that I wanted to change lights up kinda yellowish/green and yeah it has 1.8v but what about the other one it doesn't have any V readings BUT the light is lit so what is this led??? Btw the other light that I'm trying to change is a cool white led, sorry for not mentioning it. Yeah it has 2 5mm leds and a small square led. The mesurments taken were made off circuit.

 

[rjenkinsgb]

Try something like a 9V battery or 12V PSU with a 1K series resistor to limit the LED current to a safe level, and measure the voltage across a good LED in the lights?

 

[Diver300]

On most multimeters, when the diode test function is selected, the meter attempts to put out a constant current, maybe 1 mA. The meter measures the voltage and displays it, but usually only up to a certain voltage, maybe 3 V. Anything above that is shown as no connection.

The constant-current generator will work to a higher voltage, maybe 6 V.

For the LED to light, it needs is for the circuit being tested to have a voltage between 3 and 6 V while 1 mA is flowing and you will get the behaviour that you saw.

 

[Serge 125]

Ok so what I can see is that my ORG white led is over the 2V that the meter can't measure and the one that I wanted to change it with is just 1.8V and the meter can measure it and that the circuit isn't made for the 1.8 but for the 2+V leds (like the white ones) right?

 

[Serge 125]

So am I right about what I said in my last message or wrong?

 

[Diver300]

Ok so what I can see is that my ORG white led is over the 2V that the meter can't measure and the one that I wanted to change it with is just 1.8V and the meter can measure it and that the circuit isn't made for the 1.8 but for the 2+V leds (like the white ones) right?

White LEDs are always over 2 V, so it's no surprise that the meter can't read the LED voltage if the meter has a limit of 2 V.

It's very difficult to know the circuit is arranged so it's difficult to know the effect of a lower voltage LED.