WR841 16MB Flash Mod
The router "TP-Link WR841N" enjoys extreme popularity in Freifunk communities because it is extremely inexpensive, has good RF characteristics, supports MIMO and has relatively high CPU power.
On the Freifunk routers a software called Gluon is used, which is based on OpenWRT.
With the (temporary) switch to LEDE in early 2017, the images became increasingly larger and slowly reached the limit of the 4 MiB flash memories that the 841s have. Therefore the Freifunk-Forum had the idea to exchange the SPI flash devices of these routers.
Apart from the mechanical change of the SOIC8-SMD component, some software changes still have to be made. Fortunately, there is a modified version of the bootloader u-boot, which automatically recognizes larger flash devices based on their JEDEC ID.
Before removing the old flash chip, you should backup and download the two flash partitions /dev/mtd0 (u-boot) and /dev/mtd4 (ART) using an OpenWRT or LEDE-based image. These have to be written back to the new flash later, otherwise the Wi-Fi chipset cannot be initialized.
I have explained the exact process of the flash chip swap in this video: