PS3 Booting Debug Firmware Guide
Here's how to do it, not sure if it matters, as it's been out here for quite a while now..
Note, this should not be attempted unless you know what you are doing, as it could lead to bricks
1. Get otheros++ running on 3.41 or 3.55, I used 3.41 but 3.55 should work as well.
2. boot linux, and dump your nor flash, with
dd if=/dev/ps3nflasha of=nor.bin
3. ensure that /dev/ps3dmproxy exits, if not look here - ps3devwiki.com/index.php?title=OtherOS%2B%2B#ps3dm-utils
4. download and compile ps3dm-utils..
5. dump your ipds, with
./ps3dm_aim /dev/ps3dmproxy get_dev_id
6. now open your nor dump with a hex editor searching for your ipds, you should find it twice, replace the 6th byte with 82 on both of them
7. Flash the nor.
dd if=modifiednor.bin of=/dev/ps3nflasha
This takes a while..
8. Prepare a flash drive for service mode, with the 3.41 debug firmware - do not flash a higher firmware - as well as a lv2diag.self
9. Finally, flash that as if you were downgrading, and you are now on a full debug firmware...
NOTE- all of the info on how to do this was found on ps3 dev wiki, so if you run into problems, you'd wanna look there.