how to locate the root cause of a corrupted ext3 filesystem

I have a 4G Compact Flash card with a 2.5G ext3 partition. The file system has become corrupted. I am not necessarily interested in fixing the file system as identifying exactly what is corrupted in the filesystem. Aside from knowing outright the filesystem is corrupted, when running GNOME's Disks utility, if I select the partition and select to 'repair the filesystem', it eventually errors with: Error repairing filesystem on /dev/sdb3: Process reported exit code 1: e2fscf 1.42.9 (28-Dec-2013) (udisks-error-quark,0) I got the idea from here to use badblocks to try to identify bad blocks, get inode numbers, and find corrupted files. however when I run this, badblocks didn't find any badblocks (ran a few times) sudo badblocks -v /dev/sdb3 -b 4096 -s Checking blocks 0 to 622517 Checking for bad blocks (read-only test): done Pass completed, 0 bad blocks found. (0/0/0 errors) I thought this was odd, so I ran fsck, but that reported no errors either:

sudo e2fsck -vcck /dev/sdb3
e2fsck 1.42.9 (28-Dec-2013)
Checking for bad blocks (non-destructive read-write test)
Testing with random pattern: done                                                 
/dev/sdb3: Updating bad block inode.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information

/dev/sdb3: ***** FILE SYSTEM WAS MODIFIED *****

      243306 inodes used (78.16%, out of 311296)
         134 non-contiguous files (0.1%)
         121 non-contiguous directories (0.0%)
             # of inodes with ind/dind/tind blocks: 2469/39/0
      583752 blocks used (93.77%, out of 622518)
           0 bad blocks
           0 large files

      210273 regular files
       28804 directories
         638 character device files
          12 block device files
           1 fifo
        2646 links
        3569 symbolic links (3480 fast symbolic links)
           0 sockets
------------
      245943 files

Now I am confused. what does it mean that I cannot repair the filesystem, yet filesystem checker and badblocks tell me nothing is wrong. Is it just a mechanically failed CF card then? Anticlimactic...It is new after all.