Youku YK1 OpenWrt 18.06.4 Bad Magic

Hello, I downloaded
https://downloads.openwrt.org/releases/18.06.4/targets/ramips/mt7620/youku-yk1-squashfs-sysupgrade.bin

sha256sum is
287db0240ef81a74ed72f559b0455e21b534cec21769222267a92e49b283a8fd

and write to my router by command:
mtd write youku-yk1-squashfs-sysupgrade.bin firmware

reboot
I get this result:

U-Boot 1.1.3 (Oct 19 2015 - 10:09:07)

Board: Ralink APSoC DRAM:  128 MB
relocate_code Pointer at: 87fb8000
enable ephy clock...done. rf reg 29 = 5
SSC disabled.
spi_wait_nsec: 29 
spi device id: c2 20 19 c2 20 (2019c220)
find flash: MX25L25635E
raspi_read: from:30000 len:1000 
*** Warning - bad CRC, using default environment

============================================ 
Ralink UBoot Version: 4.2.1.0
-------------------------------------------- 
ASIC 7620_MP (Port5<->None)
DRAM component: 1024 Mbits DDR, width 16
DRAM bus: 16 bit
Total memory: 128 MBytes
Flash component: SPI Flash
Date:Oct 19 2015  Time:10:09:07
============================================ 
icache: sets:512, ways:4, linesz:32 ,total:65536
dcache: sets:256, ways:4, linesz:32 ,total:32768 

 ##### The CPU freq = 580 MHZ #### 
 estimate memory size =128 Mbytes

Please input the operation:                                                                                                                0 
   
3: System Boot system code via Flash.
## Booting image at bc050000 ...
raspi_read: from:50000 len:40 
Bad Magic Number

my question is how to de-brick or how to enter u-boot console?

thanks,
zhang