As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT GROUNDED. GEN 1 LOSS TRANSFER BUS FAIL ALL INSTRUMENTS OFF EXCEPT F/O PFD. FOUND GEN CONTROL UNIT #1 UNLOCKED AND SLID OUT OF RACK APPROX 3 IN RESECURED #1 GCU AND PERFORMED OPS CK IAW B737-400 AMM 24-21-81-404-007 AND 24-21-81-705-001 ALL CKS GOOD