ejolson
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Joined: Tue Mar 18, 2014 11:47 am

No Red LED [solved]

Wed Sep 12, 2018 4:29 pm

I have a Pi 2B and the red LED seems dark now. If remember correctly it used to light up. The system otherwise seems functional.

So what does it being dark mean? Is this a low voltage indicator, a burned out light, software changes or something else?

If you have a 2B running the latest Raspbian, is the red LED illuminated while the system is powered?
Last edited by ejolson on Wed Sep 12, 2018 9:22 pm, edited 1 time in total.

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mahjongg
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Re: No Red LED

Wed Sep 12, 2018 4:41 pm

A 2B has the undervoltage protection circuit, which turns the power LED off when the input voltage drops under 4.65V, but you should also get a lightening icon when that happens.
In principle software can turn the LED off, if the GPIO that senses an undervoltage is switched to an output, and outputs a low, that will turn the FET that drives the LED off.
Otherwise I would not know why the LED would be dim, except when the 3V3 supply drops to a far lower voltage, but then the PI would also stop working.

often the power (micro-USB) cable is the source of low input voltages.

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allfox
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Re: No Red LED

Wed Sep 12, 2018 4:43 pm

My BCM2836 Pi 2B's red LED is illuminating here.

ejolson
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Re: No Red LED

Wed Sep 12, 2018 4:55 pm

mahjongg wrote:
Wed Sep 12, 2018 4:41 pm
A 2B has the undervoltage protection circuit, which turns the power LED off when the input voltage drops under 4.65V, but you should also get a lightening icon when that happens.
In principle software can turn the LED off, if the GPIO that senses an undervoltage is switched to an output, and outputs a low, that will turn the FET that drives the LED off.
Otherwise I would not know why the LED would be dim, except when the 3V3 supply drops to a far lower voltage, but then the PI would also stop working.

often the power (micro-USB) cable is the source of low input voltages.
There is no monitor connected so I'm not sure about the lightning icon. Thanks, I will swap power supplies and report back.

W. H. Heydt
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Re: No Red LED

Wed Sep 12, 2018 5:22 pm

allfox wrote:
Wed Sep 12, 2018 4:43 pm
My BCM2836 Pi 2B's red LED is illuminating here.
I was going to point out that there are two--rather different--versions of the Pi2B.

ejolson
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Joined: Tue Mar 18, 2014 11:47 am

Re: No Red LED

Wed Sep 12, 2018 9:21 pm

W. H. Heydt wrote:
Wed Sep 12, 2018 5:22 pm
allfox wrote:
Wed Sep 12, 2018 4:43 pm
My BCM2836 Pi 2B's red LED is illuminating here.
I was going to point out that there are two--rather different--versions of the Pi2B.
This is one of the original Pi 2B computers. Seems a different power supply did the trick. The red light came on and has remained lit for a couple hours now. I'll mark the topic as solved. Thanks for the help.

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