Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

LED diode type needed to fix??

Serge 125

Member
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

Member
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?
 

Serge 125

Member
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

Well-Known Member
Most Helpful Member
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

Well-Known Member
Most Helpful Member
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

Member
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?
 

Diver300

Well-Known Member
Most Helpful Member
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.
 

Latest threads

New Articles From Microcontroller Tips

Top