Slt,
Il est désormais possible de passer l'ET4000 de 500 à 750 Mhz avec le dernier bootloader !
Imageversion: openpli-4-20140225
Bootloader upgrade
1. Unzip the attached file then 'et4x00' folder will be appeared.
2. Copy that folder into the USB medium
3. Insert USB medium into either USB sockets on the front or rear panel.
4. Power Off and Power On using the power switch at the rear panel of the box.
5. After Power On, ET4000 model will detect if there is his software available on the USB medium.
6. Press ‘CH – ‘ button on the front panel.
7. ET4000 model gets into state of upgrading.
8. The box will startup automatically after the upgrade is finished.
-Warning-
During upgrading, please don't unplug power or shut down STB.
Don’t power off within 5 seconds after upgrade is completed.
-Important Note-
Don’t upgrade the Bootloader and Firmware at the same time.
Make sure that in the USB stick only needed files for either Bootloader or Image should be contained
while processing for either Bootloader upgrade or Image upgrade.
Ils indiquent quand même que les inconvénients qui peuvent en découler ne sont pas encore connus donc attention quand même
Infos et fichiers ici :
http://www.et-view-support.com/Forum/showthread.php?13813-ET4000-500-auf-750MHz-Upgrade 
