FUZE+ bootloader USB mode OK but refuses to boot either on RockBox or OF

[lmk]

Hi,

I hope I've posted this message to the correct section as I'm new to rockbox.

RockBox was running fine on my FUZE+ for the last 15 days after the Rockbox installation but it now refuses to boot :
- booting with RockBox gives a black screen
- no way to boot with OF
- with an AC-only adapter the device does not stop looping on the boot screen

Luckily BootLoader USB Mode is OK as is also ChipSet HID recovery mode

The device went wrong like this after disconnecting it from my PC when in Bootloader USB mode (as described in another post, you need to reset fuze+ to get it working again in that case, but it did not do the job)

As I suspected some fileSystem corruption, I've run a dosfck ( with NO automatic fixes ! ) on the device :
laurent@noiraud:~$ sudo dosfsck -n /dev/sdb1
dosfsck 3.0.12, 29 Oct 2011, FAT32, LFN
There are differences between boot sector and its backup.
Differences: (offset:original/backup)
  71:4d/4e, 72:45/4f, 73:55/20, 74:50/4e, 75:45/41, 76:55/4d, 77:33/45
  , 78:2d/20, 79:4c/20, 80:4d/20, 81:4b/20
  Not automatically fixing this.
/dev/sdb1: 1635 files, 22865/119096 clusters

As I'd like to fix this I've got several questions :
- would it be safe to fix the boot sector, retrieving the backup boot sector ? Does it make sense ?
- if I screw up the /dev/sdb1 while doing this, will the bootloader USB mode be still available for me to restore original boot sector ? Is unix dd fine for this ?
- is there some documents describing the boot process/software layers for a noob ?
- is there a log of the boot process available somewhere in the file system ?
- should I look for a OF restore as a first step before reinstalling Rockbox ? With the HID recovery mode ?

Last but not list, is there a way to search only for posts containing 'fuze+' in this forum ?
Searching 'Fuze+' also returns everything about older Fuze devices, wich makes it very difficult to find usefull information.

Thank you for your help :-)

[lmk]

Great ! Rockbox's back on my fuze+ !

I assume the problem was the low battery : the device would execute the first step of the boot process and shutdown because of low battery ?
As I think I've read somewhere, the fuze+ would not refuel battery when in bootloader USB mode.

Trick : boot in OF USB mode.
Press volume down and connect to computer (I also pressed the power on button when connected but do not know if it did anything). Once connected with OF, wait for some minutes to get your battery refueled.
Unplugg. Restart. Enjoy.

Hope this will help.

However I'd be glad if I could get some answers to my questions :-)