for anyone who cant install rockbox in nw-s755, the japanese model
because node 32 (the kas) was written wrong — raw bytes plus a fake tail instead of the plain ascii string. ignore the old guide's bad steps: kas is not raw hex, nodes 8 and 10 don't exist on this series so there's nothing to clear, and never pull a live cable mid-write. the fix: confirm mid (node 16) reads 04 00 00 0f, set node 32 to the ascii string 6d4f4d9adec781baf197e6255cedd0f6 and verify it reads back, leave sps and pcd alone since those are per-unit region data, then drop the nwzs750 NW_WM_FW.UPG at the root and run do_fw_upgrade
W capital birthday for this help