What was found
FLT 2423. FIRST TRANSISTION SOUNDED CLEAR, BUT CRACKLY. DURING SUBSEQUENT TRANSMISSIONS BTWN GATE & RUNWAY, SIDETONE BECAME LESS & LESS. GROUND DID NOT COMMENT ON QUALITY. AFTER T/O, DEPARTURE FREQ. STARTED TO REPORT THAT WERENT TRASMITTING CLEARLY. AFTER 20 MINS UNABLE TO TRANSMIT ON COMM 1 FROM EITHER SEAT IN A WAY THAT WAS UNDERSTANDABLE. CHKD MULTIPLE TIMES. AT TIMES THEY DID NOT HEAR AT ALL, & THEY REPORTED BROKEN & UNREADABLE, RETURNED TO FIELD & REMOVED FROM SERVICE. REPLACED FO'S PTT/HOT MIC SWITCH IAW MM 23-51-03-000/400-801-A. PERFORMED VHF COMMS SYS FUNCT TEST , VERIFIED NR 1 VHF COMM TRANSCEIVER HAS BAD POWER OUTPUT, IAW MM 23-12-00-720-801-A. REPLACED VHF MODULE, ALL OPS CHKD GOOD IAW MM 23-12-01-000/400-801-A. RETURNED TO SERVICE.