I have the same exact problem with a stock Beaglebone Black a5a board. The 
board used to work fine. I shut it down for a few months. I went to plug it 
in and no usr lights flashed. Only the power light flashed. I as you, went 
to see what was wrong and hooked up a USB to serial on the UART rx, tx, gd 
to see the output. As soon as I applied power to the board it booted with 
an SD card. When I take the SD card out it boots as well. However if I 
don't have anything hooked up to the UART rx, tx, gd no boot, just a power 
light comes on. 

Does anyone know how to fix this permanently or what has caused this? 

On Thursday, January 9, 2014 11:14:01 PM UTC-8, nitesh singh wrote:
>
> Hi, 
>
> I am using a customised Beaglebone Black, whose schematics is very close 
> to Original Beaglebone Black.  You can say we cloned the Beaglebone black 
> hardware and assembled the board.
>
> Now I used Robert C Nelson's Debian wheezy emmc flasher image sd card to 
> boot it for first time , and wrote the emmc. Then I dumped binary data 
> copied from EEPROM of one of the original beaglebone black's eeprom to the 
> eeprom on this.
>
> So, now the issue that i am facing is that, this board will not boot up 
> again from emmc or another sd card that i use, other than the flasher sd 
> card. 
> Then accidently or by chance, i tried to look at its UART0 port from UART 
> port on the other beaglebone black and it booted up as usual. 
>
> After that i observed that this customised beaglebone black is booting 
> only when the UART0 is accessed on another Beaglebone black or just simply 
> connected to its UART.
>
> What can be the problem here ? The emmc flashed on another original 
> beaglebone black is working fine, just this customised board will not boot 
> in the usual manner. 
>
> I was reading through the minicom output at UART0 for this custom board, 
> it gave some read errors, and also said that mmcblk0boot0 and mmcblk0boot1 
> does not valid partition table. 
> What are these partitions and is it possible to write or create any 
> partitions on them ?  I have seen that they are there on other beaglebone 
> blacks and mmcblk0 changes to mmcblk1 if booted from sd card, I could not 
> understand its function. Is this creating any problem with the bootup ? I 
> suspect the eeprom data also might be causing this error.
>
> I have attached the minicom output file for the custom board's UART0 port 
> while it was booting. 
>
> One more thing, it seems, connecting only DGND and UART0_RX to another 
> board is sufficient to make it boot. So it is reading some data over Uart0, 
> is it to do with eeprom ?
>
> Please help. 
>
> Thanks and regards, 
> Nitesh
>

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