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Alternate PWR LED Header

post #1 of 7
Thread Starter 
Hey,
I just got back my motherboard from RMA & I've already assembled everything but then I realized my Power LED wasn't working, (No Voltage on my DMM).

Since it wasn't worth another RMA (already assembled), I took the +ve terminal of the JFP1 + & the GRD of JFP2 & the voltage was 5V on the DMM. AFAIK the voltage on PWR LED is 3.3V.

So, I'd like to know that is the LED safe to use in my "alternate" way, i.e.

a) Is the current limiting resistor already provided within the headers.
b) Is the LED safe to use at 5V.

P.S. LED glows correctly @ the "alternate" connection.
post #2 of 7
First, have you double checked the pinout to be sure you've connected the LED to the right pins? Some motherboards use a 3-pin connection for the power LED while others (newer MBs) use a 2-pin connection, which is why the LEDs often have individual connections for each lead of the Power LED.


To address your other questions; the LED headers on the MBs are logic level outputs, where ~0 V is a logic 0 (off) and 3.3-5 V is logic 1 (on). The LEDs used as case indicators are rated to operate on 5V.
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RAD GT
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post #3 of 7
Thread Starter 
Quote:
Originally Posted by radodrill View Post
First, have you double checked the pinout to be sure you've connected the LED to the right pins? Some motherboards use a 3-pin connection for the power LED while others (newer MBs) use a 2-pin connection, which is why the LEDs often have individual connections for each lead of the Power LED.
Yes, LED worked fine before giving for RMA. The guy only replaced a burnt MOSFET. Confirmed using the my DMM, no Voltage on PWR LED Pins.

[QUOTE=radodrill;13173816
To address your other questions; the LED headers on the MBs are logic level outputs, where ~0 V is a logic 0 (off) and 3.3-5 V is logic 1 (on). The LEDs used as case indicators are rated to operate on 5V.[/QUOTE]
So, am I breaking the max limit, 'coz the voltages may fluctuate a bit.
post #4 of 7
Quote:
Originally Posted by nbaztec View Post
So, am I breaking the max limit, 'coz the voltages may fluctuate a bit.
The case LEDs will be fine on either 5V or 3.3V, the slight fluctuations in voltage will not be a problem.
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RAD GT
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post #5 of 7
Thread Starter 
Thanks a ton, good to know that.
So the 12V fan headers might burn it or even those are safe (I'm sensing a strict No).
post #6 of 7
12V headers will burn out the LEDs unless you are using the appropriate current limiting resistor in series with the LED. The actual resistance required depends on the specs of the LED.
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RAD GT
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post #7 of 7
Usually LEDs like that use around 20mA, so if you wanted to run it off 12V you'd want to add a 350 ohm resistor in series with the LED.

0.02A = 5v/R; R = 250; 0.02A = 12V/250+x; x=350
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Labor of Love
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