TRANSPONDER NOT WORKING?  CAUTION:  IT IS UNLAWFUL TO FLY INTO A TCA WITH A KNOWN DEFECTIVE TRANSPONDER, EVEN FOR TROUBLESHOOTING.  REMOVAL OF ENCODER MAY REQUIRE A STATIC LEAK CHECK.  ANY REPAIRS MUST BE PERFORMED BY PROPERLY AUTHORIZED AND LICENSED PERSONS.

Transponders are not difficult to troubleshoot to the box level.  There are just 3 interfaces: Power, Antenna & Encoder.  If your transponder loses contact with any you have problems.  The behavior of the reply lamp is the most valuable tool. REMEMBER:  You can print any of these pages and pass them along to your mechanic.

I ALREADY KNOW MY TRANSPONDER IS DEFECTIVE.  I JUST WANT IT FIXED. I WANT A PRINTABLE PAGE I CAN TAKE TO THE AIRPLANE WITH ME.

MAIN TROUBLESHOOTING PAGE  Turn your transponder on.  A healthy transponder will normally display these characteristics: 1. Reply lamp comes on during warm-up. (Most units). 2. A high pitch whine might be heard if you listen very closely. 3. Reply lamp goes off in 15-30 seconds. 4. Reply lamp will come on if unit is placed in test mode. 5. Reply lamp will come on for about 15 seconds if IDENT button is pressed. 6. Reply lamp flashes during flight.   IF NONE OF THE ABOVE OCCURS.   IF ALL OF THE ABOVE OCCURS.   IF REPLY LAMP DOES NOT COME ON IN FLIGHT.   IF REPLY LAMP DOES NOT COME ON WHEN UNIT IS IN TEST MODE.   IF REPLY LAMP IS ALWAYS ON AND DOES NOT FLASH   IF ATC REPORTS YOUR TRANSPONDER IS INTERMITTENT.   IF ALTITUDE REPORTING (MODE C) IS INOP OR IN ERROR.