As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU DIFFICULT TO PUT ON TRANSFER BUSSES. MULTIPLE ATTEMPTS MADE AFTER APU "GEN OFF BUS" LIGHT ILLUMINATED. TOOK APPROXIMATELY 2 MINUTES AFTER APU WAS AVAILABLE BEFORE TRANSFER BUSSES WOULD CONNECT TO APU. DID NOT NOTE VOLTS/FREQS OF APU GEN WHEN TRANSFER BUSSES COULD NOT BE CONNECTED TO APU POWER. GROUNDED - YES. REMOVED AND REPLACED APU STARTED/GEN, REF B737-800 AMM 49-41-21. OP CHECK NORMAL, NO FAULTS OR LEAKS NOTED.