What was found
DURING CLIMB-OUT THROUGH FL290 MULTIPLE ELECTRICAL EQUIPMENT FAILURES OCCURRED. ALL GENERATOR & TRANSFORMER RECTIFIER INDICATIONS NORMAL. A TRANSFER BUSS CIRCUIT BREAKER FOUND TRIPPED. AFTER A COOLING PERIOD CREW RESET CIRCUIT BREAKER. ALL SYSTEMS RETURNED TO NORMAL & CREW CLIMBED BACK INTO RVSM AIRSPACE. ONCE LEVEL, SAME BREAKER TRIPPED AGAIN CAUSING SAME MULTIPLE SYSTEM FAILURES. AS PER COMPANY PROCEDURES & MANUFACTURER RECOMMENDATION, CREW DID NOT RESET TRIPPED BREAKER A SECOND TIME. CREW THEN ADVISED THAT THEY NEEDED TO RETURN. ON DESCENT, CABIN ALTITUDE WARNING HORN ACTIVATED. CABIN SLOWLY CLIMBING AT 200 FT PER MINUTE. CREW CALLED FOR & COMPLETED APPROPRIATE CHECKLIST & MANUALLY REGAINED CONTROL OF CABIN. CABIN REACHED A MAX ALTITUDE OF 11,000 FT. CREW ADVISED ATC THAT THEY NOW HAD A CABIN PROBLEM & REQUESTED LOWER. ACFT BURNED OFF FUEL TO GET TO BELOW MAXIMUM ALLOWABLE LANDING WEIGHT & PROCEEDED FOR AN UNEVENTFUL LANDING. AFTER EXTENSIVE TROUBLESHOOTING, MX REPLACED THE NR 1 TRANSFER BUSS, NORMAL CIRCUIT BREAKER & FOR PRECAUTIONARY MEASURES REPLACED NR 1 TRANSFER BUSS RELAY. DURING AN EXTENSIVE TESTING PERIOD & GROUND OPERATIONS, DEFECT COULD NOT BE DUPLICATED & ACFT RELEASED FOR TEST FLT. NO FURTHER OCCURRENCES OF DEFECT NOTED ON TEST FLT. ACFT RETURNED TO SERVICE.