Beaglebone Black cant boot from emmc

I have two beaglebone black, all two board works well in the past.
Today one board fails(my lcd screen turn black), so I power off it and try a restart, but after that it never bring up again.

I attached TTL line to J1 to see what happened
1, With no sd card insert, S2 button not pressed, power on, there is no message out on my putty console, just nothing.
2, I insert sd card and pressed S2 button, power on, I can see boot messages and the board boot up success.

I wonder whether emmc is crash or something else, so I use dd to clone the first 2M data from emmc

dd if=/dev/mmcblk1 of=bad-2m.img count=16 bs=128k

It success to clone data into file.

From the good beaglebone black board, I get the same emmc img file, good-2m.img

I compare these two file and they are same, that means the MLO and u-boot.img is well in emmc.
So I doubt the problem may be hardware problem, maybe:
1, The power on initialize of emmc goes wrong, so the am335x rom code get wrong MLO binary
2, The am335x boot sequence wrongs, it does not boot from emmc by default.

Do someone else faced same situation?
Or what can I do to debug what happened?

Hi, I have found the reason at last.
The SYS_BOOT[0] become as 1, bbb SYS_BOOT[4…0] should be 11100 or 11000.
But now it becomes 11101 or 11001 , so the onboard emmc boot fails.

在 2017年6月6日星期二 UTC+8上午11:13:08,ymc1…@gmail.com写道: