Help needed recovering a device and finding root cause

Hi guru's, hope you can help me,

I have here devices (RMAs) based on a HLK 7628N, running OpenWRT19.07 (custom image).

They appear to be having boot issues: when connected to the serial console, trying to access the response is "Failed to execut". (full output below)

I am able to enter fail-safe mode but trying to recover following instructions ( are futile:

  • Soft factory reset: firstboot && reboot now → No effect
  • Hard factory reset: umount /overlay && jffs2reset && reboot now → no effect
  • Hard factory reset: dd if=/dev/zero of=/dev/loop0 bs=1M; reboot → no effect

Basically I have two questions:

  • Is it possible to recover (and how)?
  • What could have caused this? (the RMAs did pass all the factory tests)

With kind regards,

Output from the console:

XXXX - bootloader version: U-Boot 1.1.3 (Dec 16 2020 - 11:19:43)

Board: Ralink APSoC
DRAM:  128 MB
relocate_code Pointer at: 87f68000
flash manufacture id: ef, device id 40 19
find flash: W25Q256FV
Ralink UBoot Version:
ASIC 7628_MP (Port5<->None)
DRAM component: 1024 Mbits DDR, width 16
DRAM bus: 16 bit
Total memory: 128 MBytes
Flash component: SPI Flash
Date:Dec 16 2020  Time:11:19:43

Please choose the operation:
   1: Load system code to SDRAM via TFTP.
   2: Load system code then write to Flash via TFTP.
   3: Boot system code via Flash (default).
   4: Entr boot command line interface.
   7: Load Boot Loader code then write to Flash via Serial.
   9: Load Boot Loader code then write to Flash via TFTP.                     0

3: System Boot system code via Flash.
## Booting image at bc050000 ...
   Image Name:   MIPS OpenWrt Linux-4.14.221
   Image Type:   MIPS Linux Kernel Image (lzma compressed)
   Data Size:    1374907 Bytes =  1.3 MB
   Load Address: 80000000
   Entry Point:  80000000
   Verifying Checksum ... OK
   Uncompressing Kernel Image ... OK
No initrd
## Transferring control to Linux (at address 80000000) ...
## Giving linux memsize in MB, 128

Starting kernel ...

Press the [f] key and hit [enter] to enter failsafe mode
Press the [1], [2], [3] or [4] key and hit [enter] to select the debug level
Please press Enter to activate this console.

Failed to executPlease press Enter to activate this console.

depends on what's broken ...;a=commit;h=671c9d16e382bcace441d8ad07816f8ceeed3612
if you want the custom image it initially came with, ask the vendor, but TFTP is a good start.

it's using a custom black box image, we can't tell, ask the people who made it.

if you want to make it more readable, you could try to enable serial output for the
kernel, by changing the bootargs in U-boot.