Chosen Solution
I just replaced my ipod 160GB (thin) classic’s motherboard which I’d previously installed a 256GB SSD drive into with no issues. Since the motherboard replacement, windows and Itunes only reads the drive as being 128GB instead of 256. I got the correct mother board, all the serial numbers match up and everything. Not sure what’s happening here but it’s really frustrating.
The board you put in may have an older version of firmware which doesn’t recognize the larger drive. If you can still access your older board see if you can read the firmware level as well as what your new board has are they the same?
