I had OpenWrt installed on my Archer C7 v5 for a while. I wanted to return to TP-Link firmware. I tried to get it done via installed Luci web interface (don't do this!). Router didn't recover.
After restart I had only still power LED. I found about tftp recovery mode but it didn't work for me. I connected via UART, but one line on the PCB is not connected to the PIN. I try to solder it, but my skills where to low. I found solutions as you can see on the photos below. I put a needle trough a cable and hold it to the line on PCB while turning on router in recovery mode. Than I was able to send commands to the router.
It was some time ago, so I don't remember all the commands.
More on this topic:
https://openwrt.org/toh/tp-link/archer-c5-c7-wdr7500#serial
https://www.reddit.com/r/openwrt/comments/en8845/archer_c7_v5_debricking/
https://forum.openwrt.org/t/archer-c7-v5-revert-to-stock-firmware/44864/6
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=5bdd238b634a34b038fbea9046893de29a77c000
https://forum.openwrt.org/t/solved-archer-c7-ru-v5-tftp-install-does-not-works/28946
ath> tftpboot
Trying eth0
dup 1 speed 1000
*** Warning: no boot file name; using '0200A8C0.img'
Using eth0 device
TFTP from server 192.168.0.10; our IP address is 192.168.0.2
Filename '0200A8C0.img'.
Load address: 0x81000000
Loading: #################################################################
#################################################################
removed many similar lines
#################################################################
#######################################
done
Bytes transferred = 15504354 (ec93e2 hex)
ath> erase 0x9f020000 +ec93e2
Erasing flash...
First 0x2 last 0xee sector size 0x10000 238
Erased 237 sectors
ath> cp.b 0x81000000 0x9f020000 0xec93e2
Copy to Flash... write addr: 9f020000
done
ath> reset
U-Boot 1.1.4 (Mar 8 2018 - 16:34:18)
ap152 - Dragonfly 1.0
DRAM: 128 MB
Top of RAM usable for U-Boot at: 88000000
Reserving 413k for U-Boot at: 87f98000
Reserving 16448k for malloc() at: 86f88000
Reserving 44 Bytes for Board Info at: 86f87fd4
Reserving 36 Bytes for Global Data at: 86f87fb0
Reserving 128k for boot params() at: 86f67fb0
Stack Pointer at: 86f67f98
Now running in RAM - U-Boot at: 87f98000
Flash Manuf Id 0xef, DeviceId0 0x40, DeviceId1 0x18
flash size 16MB, sector count = 256
Flash: 16 MB
Using default environment
In: serial
Out: serial
Err: serial
Net: ath_gmac_enet_initialize...
Fetching MAC Address from 0x87fbafdc
ath_gmac_enet_initialize: reset mask:c02200
athr_mgmt_init ::done
Dragonfly ----> S17 PHY *
athrs17_reg_init: complete
SGMII in forced mode
athr_gmac_sgmii_setup SGMII done
: cfg1 0x80000000 cfg2 0x7114
eth0: 00:00:29:ad:00:00
eth0 up
eth0
Setting 0x181162c0 to 0x41822100
[NM_Error](nm_api_checkInteger) 00384: extra-para:a6 3b
[NM_Error](nm_api_checkInteger) 00389: factory boot check integer flag is not 1.
Hit any key to stop autoboot: 0
Trying eth0
eth0 link down
FAIL
Trying eth0
dup 1 speed 1000
HTTP server is starting at IP: 192.168.0.1
HTTP server is ready!
After that I browse for TP-Link stock firmware, flashed it through web interface (192.168.0.1) and it came back. Succeed!