AF5600 with ACm and sandia STX165R transponder. AS I entered controlled airspace at altitude and 140 KTs, ATC gave me a 4400 squawk code and i was acknowledged and the reply indicator was flashing. Upon exiting airspace i must have tried putting in VFR, by button, screen, or putting in 1200 by digits, on, alt, stby and it would revert back to 4400 and alt. I tried for probably 10 minutes and just put it in standby and landed and still on the ground it would revert back to the 4400 code.

i reviewed the pilots guide and am operating the transponder as i understand the manual. Just pushing the vfr keyboard button would switch the code for about 2 seconds then revert back to the previous squawk code.

Looking for suggestions.


Keith Rhea