successful downgade complete using a teensy ++ on cechj03 with a dia-002 board.
was not a simple task but here is how i overcome some problems i had.
i started off the task by not using a voltage regulator and used the vcc from the ps3, this worked fine without any issues, created good dumps and all was fine until flashing the patched dump back, this would stop at 256k,
i moved to using the writeword command in norway.py however this give the same results.
i checked the vcc and at that point the voltage was floating about a bit and even at times dropping as low as 2.5v hence it was more than likely the nor that was failing not the flash as the vcc comes from the ps3 and the nor.
i then fitted a voltage regulator and tried the write command again once again came across the same problem still stopping at 256kb however the writeword command worked flawless and verified without problems too.
ive now fitted a switch to switch between the voltage regulator and the vcc, ive done this so i can leave the teensy++ connected and still within my ps3 but it can also be used as a factory service unit as well when the switch is set to the vcc power and if ever i need to flash i can swap back to the regulator meaning everything boots well and works without problems.
so here are my reccomendations
1 i used 30swg wire, worked without any problems on cables less than 15cm (had about 0.1 ohm resistance between the teensy and the trace on the ps3)
2 fit a voltage regulator to do the dumps as well, the voltage drop caused by the teensy++ cant be healthy for the nor chip and i was lucky i never bricked the thing.
3 dont remove the teensy++ from your ps3 for using it to get into factory service mode, just simply remove the voltage regulator and attach the vcc (no voltage drop was seen doing this so id go as far as saying its safe and better than removing the whole chip just to enter factory service mode)