- Model: MP4 Player YaGu 1521CF+
Display: Unknown 128x128 OLED display
Board: MP3-906.PCB VER:3.0
CPU: AMP2085 EA204AB EAV
Memory: Hynix KOR HY27UG084G2M TPC8 601AA M9SDA913
Radio: SPT SP3767HN 05LS06
Battery: 043048SP 3.7V 520mAh FA09
Chapter 1. Making it broke
Action: Killing my mp4 player's firmware by uploading incorrectly modded version of the firmware dump.
Result: Hourglass screen keeps showing, screen is blinking in 1-2 seconds period - clear signal that bootloader in a loop tries to load firmware and restarts after failure.
Player is not detected by computer - neither as disk, nor ADFU device.
Action: Opening the player - really hard as it needed to unglue two plaques on both sides, unscrew some really tiny screws, unglue battery soldered to the memory chip.
Action: Putting mp4 player in the ADFU mode - really easy, using a paper clip on memory unit.
Chaper 2. Trying / research
Action: Uploading some mp4player firmware from s1mp3.org site.
Result: Display went dead - black with fast white blinks, but at least player can be detected as flash disk.
Action: Formatting drive and uploading oryginal player's repaired dump file.
Result: Not as expected - player gets zapped to the state for Adfu mode.
Actions: Uploading various firmwares - for LCD/OLED displays (no full firmware for 128x128 OLED display).
Results: No results - some F/W zap the player, some make it detected as flash disk, none make display any better.
Chapter 3. Solution
After many combinations I came to this single solution that worked.
Action 1: Merge FWIMAGE.FW from oryginal repaired dump with other (top level) files from libik_FM_1GB.bin (3.5.31 FULL firmware), using script generated from libik_FM_1GB.bin.
Upload merged file.
Result: Player gets zapped.
Action 2. Put player into ADFU mode. Upload 958HY-512.fw (from s1mp3 site).
Result: Blue LEDs that are located under keyboard turn on, display stops blinking but no visuals, player detected as flash disk.
Action 3. Format flash disk using RdiskUtility.exe
Action 4. Upload oryginal repaired dump file.
Result: Everything back to normal - display, keyboard, functions etc.
Seems that having player detected as flash disk isn't enough to repair player by uploading dump file - this resulted in zapping player.
The solution is so complicated as there is no FULL firmware for 128x128 OLED mp4 player with hynix memory chip.
Uploading 958HY-512.fw probably results in a correct merge of flashdisk / display drivers and final dump file upload provides correct resource files.
Anyway it seems safe to upload various F/W types to the mp4 player as I uploaded F/W for LCD displays, with other (non Hynix) memory chip and OLED with wrong dimensions.
Whole operation took me about 10 hours spread on 3 days.
Big thanks to the maintainers of s1mp3.org site and Dead Recovery Guide.