A PLT WHO NORMALLY FILED IFR DID NOT FILE A FLT PLAN AND CONTINUED VFR INTO DETERIORATING WX CONDITIONS. THE ACFT'S XPONDER WAS MALFUNCTIONING AND THE PLT NEEDED TO RPT BACK TO WORK. WHEN THE CONDITIONS FORCED THE PLT CLOSER AND CLOSER TO THE GND AND HE OCCASIONALLY ENTERED IMC; HE COMMUNICATED WITH ATC AND WAS ABLE TO CONTINUE ON AN IFR CLRNC.

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FOR THE PAST FEW MONTHS; I HAVE HAD MULTIPLE PROBS WITH MY MODE C ALT ENCODER. I HAVE SPENT HUNDREDS OF DOLLARS IN REPAIRS DUE TO THE FACT THAT THE PROB COULD NOT BE DETECTED. THE ENCODER WAS FINALLY SENT OUT FOR REPAIRS. WHILE RETURNING TO OK FROM VA; AFTER A MONTH OF BUSINESS; IT BEGAN TO ACT UP AGAIN. UPON TKOF FROM NORFOLK INTL; IT WAS SHOWING AN ERRONEOUS MODE C. AFTER ABOUT 1/2 HR; THE PROB FIXED ITSELF; AND FOR THE NEXT 4 HRS; THE EQUIP WORKED FINE. HOWEVER; UPON CANCELING IFR AT MY FIRST STOP (DAYTON GENERAL; OH); AS SOON AS I WENT TO SQUAWK VFR; THE MODE C BEGAN TO ACT UP AGAIN. THIS WAS LATE FRI NIGHT AND THERE WAS NO ONE AROUND TO FIX IT OVER THE WEEKEND. ON SUN; I BEGAN THE REST OF THE TRIP HOME. WX WAS SUPPOSED TO BE VFR AND THE RAIN SHOWERS AND FOG WERE RPTED AS DISSIPATING RAPIDLY. NORMALLY; I ALWAYS FILE IFR; BUT SINCE MY MODE C WAS INOP; I DEPARTED VFR AS I WOULD BE TRANSITIONING VERY LITTLE CTLED AIRSPACE AND NO CLASS B AIRSPACE. NEAR FT WAYNE; IN; THE WX BEGAN TO DETERIORATE QUICKLY. THE CEILINGS AND VISIBILITY WERE DROPPING FAST AND I FOUND MYSELF SCUD RUNNING; EVEN TO THE POINT OF BRIEF PERIODS OF IMC. I WAS VERY UNCOMFORTABLE WITH THIS SIT AS I GOT CLOSER AND CLOSER TO THE GND. I WAS ANGRY AT MYSELF FOR GETTING INTO THIS SIT. FINALLY I HAD NO CHOICE BUT TO FESS UP AND XPONDER OR NOT; PICK UP AN IFR CLRNC. THE REST OF THE FLT WAS UNEVENTFUL. I MIGHT ADD THAT THERE WAS GET HOMEITIS PRESENT; AS I HAD TO BE AT WORK ON MON (MIL). SO; THE BOTTOM LINE IS THAT I LET AN EQUIP FAILURE SIT LEAD ME DOWN A POTENTIALLY DANGEROUS; LIFE THREATENING; AND ILLEGAL SIT; ALL BECAUSE I HAD TO GET HOME.