故障现象：卡在开机界面
故障原因分析：卡在开机界面，需要用U盘进行升级后强制恢复出厂是否正常，如果故障依旧，需要连接串口工具通过打印信息进行进一步判定
检修过程：卡在开机界面，需要用U盘升级失败，连接串口工具观察部分打印信息如下：
** Unable to use usb 0:2 for fatload **
** Partition 3 not valid on device 0 **
** Unable to use usb 0:3 for fatload **
** Partition 4 not valid on device 0 **
** Unable to use usb 0:4 for fatload **
hsin-upgrade
Writing to MMC(0)… [ eMMC_CheckR1Error() ] eMMC Err: eMMC_ST_ERR_R1_31_24
[ eMMC_CheckR1Error() ] eMMC Err: eMMC_R1_WP_VIOLATION
0x2C26C0D4: 0Dh 04h 00h 09h 00h 00h 00h 00h 00h 00h 00h 00h 00h 00h 00h 00h | …………….
[ eMMC_CMD13() ] eMMC: CMD13 check R1 error: 80000A04h, should not retry
[ eMMC_WriteData_Ex() ] eMMC Err: W fail: 80000A04h
0 blocks written: ERROR
上述打印信息证明EMMC损坏，更换EMMC(位号N56，型号H26M41204HPR)后故障排除
故障板号：RSAG7.820.8802
故障元件：H26M41204HPR