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You need to rebuild the U-Boot with this patch to disable the read limit. Then write the patched U-Boot to an SD-card with Armbian and boot into loader mode with the card inserted. It's also possible to patch the binary code of the original U-Boot from EMMC, but it's long to explain.

This comment describes a recovery method without shorting the pins. I haven't tried this method.

Please give at least compiled dtb's for your TV-boxes. I tried to rebuild the image for legacy kernel with the latest Armbian-build, and now HDMI doesn't work at all. Update: The problem seems to be that the TV boxes use gmac0, the driver of which is RK630_PHY, and this driver is not enabled in linux-rk35xx-vendor.config. compatible = "ethernet-phy-id0044.1400", "ethernet-phy-ieee802.3-c22"; #define RK630_PHY_ID 0x00441400 Update2: Still doesn't work, even with this driver (preinstalled Android uses this driver).

Is it like this in the dts file or did you do it another way? - ethernet0 = &gmac1; + ethernet0 = &gmac0; &gmac0 { - status = "disabled"; + status = "okay"; }; I tried this in rk3528-mangopi-m28k.dts but no luck.

Armbian now supports MangoPI M28K (BOARD=mangopi-m28k BRANCH=vendor), which uses kernel 6.1. HDMI-audio works with dtb from MangoPI. But now Ethernet port doesn't work, neither with this dtb, nor with what I did for the old kernel.

Most likely this: But did you notice that this is a "minimal" build? You need to install desktop packages if you need a desktop.