AusGameStore Downgrading service for the PS3 console can revert your current software version down to Factory 3.55. This process requires the game console for a full day and will restore version 3.55 Original Factory software ready for CFW to be installed, thus allowing extraction of your DVD drive Key. PS3 Slim Model Software Downgrade here
Why Downgrade my pS3 Console
There are New Exiting products coming out like USB game loaders that allow you to install your PS 3 Original game disc to an External 2.5 inch hard drive, then play the game from the hard drive without the Need Of The disc.
Currently most of these devices require your PS 3 Console to be running software version 3.55 or lower
if your software is higher than 3.55 your console needs to be downgraded back down to Version 3.55

First thing to check
NEW Minimum Firmware Check Guide here
what software you are currently running Check What Software Version you have click here......
Next
Not every PS3 console can be downgraded
Next check the model number of your PS3 console here....
Finally
Check Model Firmware at Release Information Here..
firmware @ release date needs to be 3.55 or lower
More Information about downgrade service here
The Downgrading hardware needs to be temporarily installed in the console to read and write the TSOP Memory chip
What is required is a connection to the data and address lines of the NOR or NAND Flash Memory chip inside the console once this is done the Nor memory can be dumped to a PC for analysis converted to lower firmware then re-flashed back to the NOR chip. If one step of the downgrade is missed the PS3 can be bricked and recovery can be difficult
Downgrading the PS3 Software is Ideal for those who want to run Linux Operating system
This downgrade is required for PS3 consoles that are running Software higher than 3.55, the many USB loaders and ODE drive emulators currently available on the market require the drive key to function.
Drive key can only be extracted if you are running Software 3.55 or lower, or have CFW installed.
Usually the console needs A program to be run from a USB stick called minimum version checker. This will tell you if your console can be downgraded. The PS3 thinks the Program is a system update, were in fact it will check if a downgrade is possible without the need to dismantle the console
The Models CECHJ02, CECHK02, CECHH02, CECH2002A,CECH2002B, CECH2502A,
seem to be fine for the Downgrade
More about PS3 Slim downgrade here

Ideally the nand should be a NOR and the Minimum Firmware release at release date should be lower that 3.55 There is more information on the console models here ........
Sounds confusing well we can do all the checking just call and book a day and time you may need to leave the console with us for a day or two, the process is quite complicated and time consuming but the benefits are you can play PS3 games from a USB hard drive.
If you are looking at getting the 3k3y installed, the Software and also the hardware needs to be compatible.
All the data and address lines need to be soldered this process is very time consuming and requires precision soldering Skills By a competent Engineer

This is a schematic diagram of the TSOP Memory chip inside the PS3 console

PS3 nor Flash Memory Chip
a View of the Memory NOR chip inside the PS3. this chip is only accessible once the console is dismantled,
and
removal of heat-sinks, until the board is completely bare.
Heat sink removed from a Playstation 3 Game console

Motherboard removed from the PS 3 chassis ready for downgrading Of The Firmware to Version 3.55
E3 Downgrader Hardware that needs to be Temporarily installed for Nor Firmware Dump