Check the user's normal cable TV signal field strength and antenna plugs and Sockets is also no exception. Teardown tuner pin voltage measurement, found its AGC control voltage is 0, forward checking TB1238AN 8 pin voltage at the output of the RF AGC voltage is 0, measuring 8 feet and no obvious external circuit elements on short circuit, judge the internal circuit is 8 feet. Considered to replaced TB1238AN price more your, and the user of wired signal of field stable, decided take points pressure of method for HF head AGC end provides fixed voltage, trial 2.2K ω received 12V power, 6.8K ω grounding, from points separate 8.5V voltage, received HF head AGC end, boot Hou, search normal, and no AGC control not normal caused of snowflake and twisted phenomenon, fault excluded.