Here's a tutorial from on "How to go back to CEX without original Flash.bin"

1. First download this CFW - 3.55 DEX Kamel

2. Install it on your PS3 either via the XMB or via the Recovery Menu.

3. Install Multiman - Multiman DEX

4. Install eEID Dumper - the link is broke need to googel this one sry all

5. Now run the EID dumper tool via the XMB. Once it has run, you will get a black screen, don't worry just turn of your console via the power button and turn back on and plug in your USB.

6. Now run multiman, find a file via the file manager, select any file > press O > open in hex viewer > press Select+start > choose yes on option dump your flash storage (Otherwise Choose NO) file will copied to USB extension .norbin (nor console) Or .nandbin (nand console)

7. Open folder dev_hdd0/temp via FTP multiman and then copy eid_root_key to usb (48bytes)

8. Download this DEX Firmware - DEX Kamel Without Downgraderand place that on your USB in the following directory PS3/UPDATE with the file name as PS3UPDAT.PUP. Install this from XMB or recovery menu.

9. Now install OpenSSL - OpenSSL 1.0.1

10. After installing it check that it has installed in the directory folder as "openssl" if it has not then simply rename its directory to openssl.

11. Download and extract the C2D Patcher to the directory. Also copy your root key and your dump file into the above directory.

12. Rename the root key into "eid_root_key.bin" and the fdump file into "in_flash.bin".

13. Run CMD (Command Prompt) via the windows menu and type in the following:

Code:
cd C:\openssl\bin
and press enter.

14. Now type in:

Code:
c2d.exe eid_key_file.bin in_flash.bin out_flash.bin 87
Replacing 87 with your console region, I'm from the UK so mine will be 87.

Here are the console regions:

Code:
82 (DEX/DEBUG) (default)
83 (JAPAN)
84 (USA/CANADA)
85 (EUROPE)
86 (KOREA)
87 (UK)
88 (MEXICO)
89 (AUSTRALIA/NZ)
8A (SE ASIA)
8B (TAIWAN)
8C (RUSIA/ASIA)
8D (CHINA)
8E (HONG KONG)
15. You will now have a new file created called "out_flash.bin" , rename that file to 355DEX.EID0.NANDBIN or 355DEX.EID0.NORDBIN depending on which console you have. Also rename eid_root_key.bin to eid_root_key, just remove the .bin extension.

16. Copy the new created BIN file and root key to your USB drive on the root then plug in the USB into your PS3.

17. Run multiman and Open filemanager then double click 355DEX.EID0.XXXXBIN in USB and Choose yes>yes>yes

18. Quit multiman and then turn of your PS3 via the PS3 controller and turn it back on via the power button.

19. Now just install CFW - KMEAW CFWand your back on CEX.

This worked for me as I was stuck on DEX For a month and also didn't want to brick my console from using the other available methods.

However there is always a risk to getting your console bricked so be careful and know this that my console is a NAND Fat model PS3.

Lastly I'm not responsible for any Bricks on your PS3, use with caution.