Question How to reset Asus k43tk bios settings

[K43tk]

Hi all friends,
Thank you for contributing in this usefull forum.
I unlocked my asus k43tk headen bios settings using a well-stablished modded bios, and it performed perfectly for some days. But then I decided to disable the weak apu graphics HD6520G to use its more powerfull discrete HD7670m as the primary (and only) graphics card.
I think I carelessly changed the settings in the northbridge menu, and after saving and restarting I got a black screen. The fan and leds are working, and HD7670m was fully functional before these changes.
I removed the CMOS battery for 3 days to reset it but no success.
Are the bios configs stored in the same BIOS flash (which is non-volatile), or perhaps in the EC (embedded controller) flash (I downloaded my laptop board schematic, it has two separate spi flash memories for "system bios" and "ec" firmware)?
I have tried to recover the bios by copying original bios file on a flash drive and renaming it several times as the SUPER, AMIBOOT, K43TK, and BIOS, all with .BIN and .ROM formats, and holding ctrl+home while turning it on; but no success.
Any help to reset the BIOS configurations to the default settings is appriciated.

 

[K43tk]

Update: I disassembled the laptop and found the two flash chip footprints on the MB. Only the EC bios flash (u42) is installed, but the system bios flash (u28 attached to the Hudson-m3 in the schematic) is not mounted on the board. Hence the EC firmware and system BIOS are both located on the same flash memory attached to the EC.
I remember I have heared that someone has shortened a pin (probably pin 2, MISO of SPI) to ground to resolve a similar problem. Am I right or this method is risky?