What was found
RDM FLIGHT NR 2142 - AFTER ENGINE START THE R TRU CAUTION CAME ON FOR ABOUT 10 SECONDS THEN WENT OUT FOLLOWED BY NR 2 AC GENERATOR CAUTION ILLUMINATING AND STAYED ON. RESET THE AC GEN NR 2 PER THE CHECKLIST RESULTED IN THE SAME SEQUENCE 1ST R TRU THEN NR 2. MAINTENANCE REPLACED THE NR 2 BRUSH BLOCK DUE TO LOTS OF CARBON BUILDUP. NO HELP. REPLACED THE AC GENERATOR AND AC GCU IAW DHC-8-200 AMM TASK 24-21-00-000-801 AND 24-21-00-720-801. FUNCTIONAL CHECKS GOOD. NO LEAKED NOTED. AIRCRAFT RETURNED TO SERVICE.