I found this post after making the same purchasing mistake. I looked up the difference between SDHC and SDXC standards, and realized that the primary difference is in the filesystem (FAT32 and exFAT, respectively).
On a mac, you can reformat that 64/128GB card and it will work perfectly well in your D40X. If you're on a mac, open up the Terminal.
Insert the card and run the command:
diskutil list
This will print out a list of all connected disks. Note the path to the card, which is /dev/disk2
in our case. Reformatting erases everything, so make sure you select the correct disk!
Replacing /dev/disk_to_format
with your path, run:
diskutil unmount /dev/disk_to_format
This will free up the device for formatting.
Replacing /dev/disk_to_format
with your path, run:
sudo newfs_msdos -F 32 -c 64 -s 67108864 -v "D40X" /dev/disk_to_format
This will format the card as FAT32, with a cluster size of 64 sectors and a total size of 67108864 sectors (32GB) named "D40X". You may be required to enter your password.
You now have a 32GB SDHC card that will work with your D40X. Restoring the full capacity SDXC simply requires you to format it back to exFAT.