AT25F1024 - ATI BIOS modification

[Andrew180]

Hi guys. I'm not a BIOS guru, but i have some specific problem.

I recently flashed a modified BIOS on my notebook's VGA. I changed HW ID of the card (i know, stupid.) and the computer won't turn on anymore. I managed to take out the BIOS chip (Atmel AT25F1024) and read it's content via ISP programmer. But here is the question: How to change the HW ID back (from 94c3 to 94c8) and flash it to the chip? I have also a dump of the original, unmodified BIOS but it's in bin format so i would need to decompile/disassemble it i guess. I don't know. I'm lost here. I'm also attaching the files.

Thanks for any kind of help.

[cp]

just search for "PCIR" in the vBIOS. the vendor id and device id are stored just behind that string in little endian encoding (1002 turns to 0210 and 94c3 to c394).
you should know this: there is a checksum calculated over the vbios contents. if you modify vendor or device id you should recalc that checksum before flashing!

[Andrew180]

Hello, thank you very much for your reply!

I figured out, how to flash the chip with the original - unmodified .bin file (which i dumped using CPU-Z before modifying anything). But the computer refuses to work anyway. I think, that the problem may be in the checksum you mentioned. I'm attaching both .bin files for comparison. They are identical, however, the original file is cutted off at 0x00062976 and the read file has FFs till the end (0x00131072). I found one thread about correcting a checksum using Hex Workshop but the illustration images are gone and I'm not able to figure it out.

I would be very grateful, if you could help me with it. Thanks!