The 8KiB block at 0xC000 has corruption in this area:
Offset(h) 00 02 04 06 08 0A 0C 0E
0000D270 FFFF 6614 FFFF 0100 FFFF 0000
0000D280 0000 6714 0C00 0100 0A00 0000 FFFF 6814
0000D290 FFFF 0100 FFFF 0000 FFFF 6914 FFFF 0100
........
0000D9A0 FFFF 0062 FFFF 0200 FFFF 0000 FFFF D908
0000D9B0 FFFF 0040 FFFF 1202 FFFF 0300 FFFF 0000
0000D9C0 FFFF 0000
If I repair it with the corresponding area of 8000_AND_A000.bin, the 8-bit sum (0x9B) is then correct, but the XOR-8 checksum is not (0x4A instead of 0x71).
Offset(h) 00 02 04 06 08 0A 0C 0E
0000DFF0 FFFF FFFF FFFF FFFF 9B00 0000 71FF FFFF
I have attached my checksum calculator and bitwise AND-ing tool.
I too found that corrupted area.
I rewrote it and confirmed that the checksum is 0x9B,4A. 9B is correct, but 4A does not match, I believe that the copied part is different between $8000 and $C000 blocks, or some byte is corrupted.
I performed a bitwise AND on the first two blocks and got the attached file. The first of the two checksum dwords at the end of the file is 0x0000002C. This matches the 8-bit sum of all the bytes preceding the checksum dword.
The 3rd and 4th blocks don't seem to fit my hypothesis, though ...
What if you were to copy the contents of the 8KiB AND-ed file to each of the 4 sections? I believe that the 3rd and 4th sections are meant to be identical, but different from the first two sections. Perhaps they contain the previous set of calibration data?
Edit:
The final dword is computed by calculating the XOR checksum of all the preceding bytes, including the previous checksum. In the present case it is 0x72, so the final dword is 0xFFFFFF72 (little-endian).
The checksum calculation does indeed match. I copied the attachment to all four blocks.
I booted it up and both the serial and model name are still initialized. I also tried reading the file to see if the initial values were overwritten, but they were not overwritten and remained at 3024. I am not sure if this is because the checksum is correct, but it may be that it is considered correct.
There was no difference in the contents of the flash ROM before and after writing.
My guess is that maybe it is only identifying the $8000 block.
The fact that it was not overwritten and remains intact means that it may still be affected by other corrupted areas and not correctly identified.
The binary that exists in $6700 is suspect. Possible contents may be storing bandwidth, sampling rate, option flags, etc.
This part could be very difficult to recover. I do not see any duplicated blocks around. It may be faster to buy a working one and dump it.
I am afraid to expose the board to hot air repeatedly, so I am currently ordering a ROM extender board. Then we will resume testing.