What was found
AIRCRAFT EXPERIENCED PARTIAL ELECTRICAL POWER LOSS. CREW WERE PERFORMING TRAINING ON RETURN LEG FROM KTEB OVER ATC APPROVED AREA NEAR HOME BASE KYIP. LEFT ESSENTIAL DC BUSS 40 AMP CIRCUIT BREAKER TRIPPED CAUSING THE 20 AMP ESSENTIAL BUSS TIE CIRCUIT TO TRIP. THIS RESULTED IN THE PARTIAL LOSS OF DC POWER. CREW REQUESTED ATC TO RETURN TO KYIP IN EMERGENCY SITUATION. REPLACED 40 AMP ESSENTIAL BUSS CIRCUIT BREAKER WITH NEW UNIT. PERFORMED ELECTRICAL LOAD CHECKS AND BUSS CHECKS IN ACCORDANCE WITH THE LEARJET 35/36/35A/36A MM-99 CHAPTER 24. AIRCRAFT TEST FLOWN FOLLOWING REPAIR WITH NO ISSUES OR DEFECTS NOTED.