So I’m trying to fix this sanitizing device. For some reason one of the LED stays ON, I checked the voltage when it is off there are 3V and ON is 12V regardless of the circuit putting the correct voltage the LED does not goes off it’s a 12V LED and stays on at 3V what do you think is going on and what ideas do you have to fix it.

 

I checked the voltage when it is off there are 3V and ON is 12V regardless of the circuit putting the correct voltage the LED does not goes off it’s a 12V LED and stays on at 3V what do you think is going on and what ideas do you have to fix it.

You're not giving us much to work with. How about a schematic?

 

it's a printed circuit board and microcontrollers I don't have the schematics but certainly I know that 10 seconds there is 12V output and then 3.8V constant throughout the 60 remaining seconds that the fan is ON. There are 2 output ports for the UV LED and both ports work the same. Strange thing is that if I switch port location UV1 to UV2 and vice versa the UV1 turns off as it is supposed to and UV2 stays ON even it is connected to the "Port that is working fine" So I tried replacing the LED because I assumed the gate transistor was broken but the new LED also remains ON.
Thanks

 

So I tried replacing the LED because I assumed the gate transistor was broken but the new LED also remains ON.

Does the LED turn off if you wait long enough? What current is the LED being operated at?

 

Does the LED turn off if you wait long enough? What current is the LED being operated at?

No it never turns off it is ON indefinitely even after the battery shuts down all the device it is ON a bit more dim.
The current is 35mA when is ON and 0 when OFF
The other one is same 35mA when ON but 2.4 when OFF

 

The other one is same 35mA when ON but 2.4 when OFF

Try putting an 820 ohm resistor in parallel with the LED.

 

Would it do the trick putting a 1.3k or 1k resistor in series so that it would turn off?

 

Try putting an 820 ohm resistor in parallel with the LED.

Could you explain why in parallel? How did you reach out that conclusion?

 

Could you explain why in parallel? How did you reach out that conclusion?

It's a WAG. You have a 2.4mA current coming from somewhere. Maybe the 820 ohm resistor will divert enough current for the LED to turn off.

This workaround is sometimes used in discrete astable/flip flop circuits where LEDs are wired incorrectly and the base current for the transistor that's on goes through the LED that's supposed to be off.

Like this, except they put the LEDs in series with R1 and R4.

 

It's a WAG. You have a 2.4mA current coming from somewhere. Maybe the 820 ohm resistor will divert enough current for the LED to turn off.

This workaround is sometimes used in discrete astable/flip flop circuits where LEDs are wired incorrectly and the base current for the transistor that's on goes through the LED that's supposed to be off.

Like this, except they put the LEDs in series with R1 and R4.
View attachment 324071

Thanks a lot, I will try to get the resistor and update if that did the trick.

 

Thanks a lot, I will try to get the resistor and update if that did the trick.

If you have 1k and 1.3k, you could try either of them. If one doesn't work, try both.

 

If you have 1k and 1.3k, you could try either of them. If one doesn't work, try both.

I finally got the chance to get some resistors and I have tried setting it up in parallel with a 1K resistor, as a result I have the same issue. I tried putting a 5K and does the same. I am intrigued what is going on. Maybe it has more to do with the other part of the PCB board components.