AN SMA PLT WITH INSTRUCTOR WAS ABLE TO FILE AN IFR FLT PLAN EVEN THOUGH HE HAD NO OPERATIVE XPONDER.

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IN RESPONSE TO DIFFICULTIES WITH MODE C RECEPTION BY ATC FACILITIES; I HAD MY XPONDER REPLACED AND THEN ADJUSTED BY A CERTIFIED AVIONICS REPAIR SHOP. IT WORKED FINE AT MY HOME BASE THE DAY BEFORE THIS FLT; AS WELL AS ON THE INITIAL PORTION OF THE OUTBOUND FLT. (THE FLT WAS AN IFR TRAINING FLT TO PRACTICE IFR FLT AND REGAIN MY IFR CURRENCY.) THE INSTRUCTOR AND I FILED FROM BUF TO AKR; WHERE WE PLANNED TO LAND; AND AFTER A BRIEF REST; RETURN HOME IFR. ALL PROCEEDED WELL UNTIL ERIE APCH TOLD US THEY HAD DIFFICULTY GETTING OUR MODE C; ALTHOUGH THEY DID RECEIVE AN INTERMITTENT REPLY WHEN WE GOT CLOSER TO THEM. THE FLT WAS FINISHED WITHOUT A WORKING XPONDER. BEFORE DEPARTING AKR; WE FILED IFR AND USED THE SLANT CODE/W TO INDICATE 'RNAV -- NO XPONDER.' BEFORE DEP; AKRON-CANTON APCH NEEDED SOME TIME TO WORK OUT OUR CLRNC ALONG OUR INTENDED RTE OF FLT BECAUSE OF THIS SLANT CODE; SINCE WE WERE NOT ONLY UNDER THE OUTER RING OF THE CAK CLASS C AIRSPACE; BUT ALSO ABOUT 3 MI WITHIN CLE CLASS B VEIL. WE DISCUSSED THE INOP XPONDER WITH THE CTLR; EXPLAINED THAT IT HAD QUIT ENRTE TO AKR AND THAT WE INTENDED TO HAVE IT FIXED AFTER WE GOT HOME. WE ALSO SHUT IT OFF AND MARKED IT 'INOP.' THE CTLR WORKED OUT A CLRNC FOR US TO GET US AWAY FROM THE CLE CLASS B VEIL TOWARDS THE YNG VOR; THEN NBOUND TOWARDS OUR INTENDED RTE OF FLT AND BACK TO BUF. WE ALSO WERE ASKED TO RPT PASSING EACH CARDINAL ALT. UPON ENTERING THE BUF APCH CTL AREA; WE ASKED FOR AND RECEIVED THEIR PERMISSION TO TRY THE XPONDER AGAIN; AND THEY RECEIVED THE REPLIES JUST FINE. THIS WAS DONE ORIGINALLY TO AID THE TECHNICIAN IN LOCATING THE PROB; BUT IT WORKED SO WELL THAT WE LEFT IT ON FOR THE REST OF THE FLT. MY NEXT FLT IS GOING TO BE VFR AROUND ALL XPONDER-REQUIRING AIRSPACE TO A REPAIR FACILITY WHERE I WILL HAVE THIS XPONDER REPAIRED. WHILE THAT IS BEING DONE; I WILL ALSO HAVE THEM INSTALL A SECOND XPONDER WITH A SECOND ENCODER AND SEPARATE ANTENNA SYS. I APPRECIATE WHAT THE CTLRS DID FOR US; BUT I DON'T EXPECT THEM TO DO THIS EVERY TIME; AND I HOPE HAVING A TOTALLY REDUNDANT ENCODING XPONDER SYS WILL PREVENT THERE BEING ANOTHER SUCH PROB FOR THEM AND ME.