105 Repetition, Replete

An older DSTA code: Can your Greater Mind take another challenge?
"Oh, no!", you must be crying out loud, "not another one!" I have to admit, it has definitely turned into an obssession and Google-ing has its wonders. After another search, I have found an older version of the DSTA code. Now, what's interesting is that, this one has a different key. And it would have been very difficult, if I didn't crack the more recent ones. Why? A quick look at the code reveals that this time the code is alpha-numeric... what the heck is 4F, 6C and 6E anyway? They are neither familiar numbers nor letters, or are they? Frankly, and very, very honestly, it was by chance from tinkering with a scientific calculator quite a long time ago, that I knew what the letter-number combinations meant. Dare try your luck once more?
PS: Credits to the author of mybloginthenet.blogspot.com for uploading this picture onto his blog.