As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PREFLIGHT IN CVG THE F/O THUMBWHEEL ON LEFT SIDE OF YOKE BEGAN TO SMOKE FOR APPROX 30 SECONDS. FOUND F/O CONTROL WHEEL MEMORY DEVICE INTERNAL SHORT. RPLD MEMORY DEVICE PER B737 AMM 33-11. OP CKS GOOD. NO EVIDENCE OF SMOKE. (LOG 8327226 - AIRCRAFT WAS GROUNDED).