Use the HDD method instead of USB & follow each of these steps to the letter:
A)
Patch the NOR
It's highly recommended to install the 4.82 official firmware twice on your console before using ps3xploit flash writer v2.0.
If your ps3 is already on ofw 4.82 then just install the 4.82 system update PUP again.
Once done, open your ps3 browser, set the homepage to http://******ps3xploit.com >Domain no Longer owned by team** (ps3xploit.me =new) >Domain no Longer owned by team** (ps3xploit.me =new) >Domain no Longer owned by team** (ps3xploit.me =new)/writer/index_nor_hdd.html
Restart the browser.
Follow the on screen instructions ie
1. download the flash_482.jpg file
2. initialize exploitation
3. patch flash
When patching is finished, you should get a success message.
To protect your console against any risk of bricking, do
NOT turn off or reboot the console just yet, you should validate the Flash memory first.
B)
Dump the patched NOR
Now set your homepage to http://******ps3xploit.com >Domain no Longer owned by team** (ps3xploit.me =new) >Domain no Longer owned by team** (ps3xploit.me =new) >Domain no Longer owned by team** (ps3xploit.me =new)/dumper/index_nor_hdd.html
Restart your browser.
Follow the on screen instructions ie
1. download the dump.jpg file
2. initialize exploitation
3. dump nor flash
When the dump is done you should get a success message.
C)
Validate the patched NOR dump
Insert a fat32 USB key in ps3.
Go to the Photo colum on XMB, select the dump.jpg file & press the Triangle button. Choose to copy the file to USB device.
On PC, rename the file to dump.hex & use PyPS3checker tool to validate the dump.
You can get this tool from the dev's github repo:
https://github.com/littlebalup/PyPS3tools
There are other dump validation tools available out there but you shouldn't use them for this because they are not updated to support ps3xploit dumps. Someone posted a thread about updating PS3DumpChecker a few weeks ago but I haven't tested the updated version if available & I have not seen any user reports about it as yet. So for now afaik PyPS3checker is the only tool guaranteed to be 100% compatible.
Read PyPS3checker_README.txt for tool requirements & usage syntax. You will need to install python 2.7.15, the Windows installer is available for download on python.org, get the 32bit or the 64bit installer, whichever is appropriate for your system.
In the PyPS3checker validation result screen, if you get either ros0 or ros1 valid with PS3Xploit 4.82 then the patch was successful, you can reboot & install the 4.82 cfw of your choosing.

All the PUP files for 4.82 CFW can be found in this forum, search the Habib/Ferrox/Rebug threads in the CFW section. Rebug CFW files must be downloaded from rebug.me.
If ever the dump isn't validated, ie you get more than 1 single ros warning, do not switch off your console & post here to get further guidance.
Hope it helps.