Successfully installed OpenWRTon my TP-Link Archer C6U. Setting up net, extroot, mount external drives. Also installed and setting up Samba server. But on my PC (Win 7) is although the server visible, but the shared folder cannot be opened. The specified path was not found, Win 7 wrote. I don't know, where is error, I've tried all.
More information is needed, because there are two SMB servers available in OpenWrt: SAMBA and KSMBD. Which one do you use? Check in the list of installed packages whether there is anything with "ksmbd" in its name.
Both your "fstab" and "samba4" files are wrong: "/dev/sda1" is a device, and you should be using the "mount point" instead. Have a look to the docs at https://openwrt.org/docs/guide-user/storage/fstab, manage to mount and access your files from OpenWrt first, then try to share them with SAMBA.