Thanks for your reply. I have scoped my regulator output and it shows a 
steady 5.38 +- 0.05 V. Besides the power pins, I only have connections to 
P9_19 and 20 to use i2c2 bus. The thing that really worries me about this 
board is that when I remove all connected items, and attempt to power with 
the USB only the behavior is unchanged. (faint flash of power led then 
nothing)

In my system I have i2c from the BBB communicating with an arduino which 
controls a stepper motor. That's it. In my mind this is fairly simple. I'm 
not sure how I could have killed the BBB this way. Should I just try to RMA 
the BBB?

I know it is difficult to diagnose the issue without seeing the specifics 
of my setup so I appreciate your help.

On Wednesday, April 24, 2019 at 10:28:32 PM UTC-4, [email protected] 
wrote:
>
> The single blink means that the Power Management Chip is going into self 
> protect.
>
> You need to put a scope on the output of your regulator and see what is 
> going on.
> 5.3 V will not fry the BBB.
> It would run fine from a 5.3 V supply that never went above 5.5V
> But it will respond the way you describe to short transients that go above 
> 5.5 or below 4.5.
> There is also a rise time spec on the start up Voltage rise.
>
> Or, it could mean that something else did fry the board, such as a blown 
> I/O pin, which is causing an over current protect on the part of the power 
> management chip.
>
> The single blink does not tell you what is wrong, just that something is 
> wrong, and the power management chip is still alive and doing its job.
>
> --- Graham
>
> ==
>
>
> On Wednesday, April 24, 2019 at 3:31:04 PM UTC-5, [email protected] 
> wrote:
>>
>> Hi There,
>>
>> I have been working on a project using a beaglebone black which I am 
>> trying to power with a 3-cell LiPo battery. To do this, I have connected 
>> the output of a hobbywing ubec 5V-3A voltage regulator to pins P9_5 and 6. 
>> This seemed to work well for a while, but just now the BBB abruptly turned 
>> off and will not turn back on. I have tried disconnecting everything from 
>> the BBB and connecting it to my PC with the USB cable. This results in a 
>> quick, faint flash of the PWR led followed by nothing. Pressing the power 
>> button with the USB cable plugged in yields the same behavior. I just 
>> tested the voltage regulator output and my voltmeter reads 5.3 V. My 
>> understanding is that the BBB requires a well regulated 5 +- 0.25 V power 
>> input. So technically my power supply is 50 mV above the limit. Is it 
>> possible that I have fried the board by doing this? Is there any way to 
>> recover it without buying a whole new BBB? Thanks in advance for your help!
>>
>>
>>

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