As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A/C WILL NOT ACCEPT EXT PWR OR GRD SERVICE PWR ALL INDICATIONS SHOW NORMAL. REPLACED BPCU, NO HELP. RE-INSTALLED ORIGINAL BPCU REF 24 42 21 400 801, REPLACED P5 4. NO HELP. RE-INSTALLED ORIGINAL P5 4 SEAMC NOTIFIED. REF MM 24 21 51 000 801. REMOVED AND REPLACED C 803 RELAY AND FUNCTIONAL CHECK NORMAL PER MM 24 21 41 400 801.