From PS3 Developer wiki
| Make sure you have several proper dumps of your flash before even trying writing to it! Use unpacking tools (e.g. Norunpack, Flowrebuilder, Norpatch etc.) and hexeditors (e.g. HxD) and use Flash page as reference.
See also: Validating flash dumps
You cannot recover from bad flash without proper dumps (e.g. bricking the console beyond repair).