As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DAY - ON TAXI OUT, CREW REPORTS NR 3 AND NR 4 CABIN COMPRESSOR OVERSPEED TEST INOPERATIVE, RETURNED TO BLOCKS. FOUND FAULTY CONNECTION AT CABIN COMPRESSOR RPM INDICATOR TO CONNECTOR PLUG. CLEANED AND RESEATED CONNECTOR PLUG AND INDICATOR RECEPTICLE TO RESTORE CONNECTION. GROUND CHECKED NORMAL. (M)