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LA3401 Multiplex Decoder

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Dan_B

New Member
I have a vintage Voice of Music receiver that works fine, but will not provide FM stereo. I replaced the original MPX board with a modern design based on the Sanyo LA3401 chip. I got the board working and restored FM stereo, but I can't figure out how to wire in the mute feature. According to the documentation, by applying 3.5v to pin 15 on the chip, FM will be muted. Ok, that works, but it mutes all sound completely. I'm wanting to mute only the static between stations. Anyone familiar with this board? Any suggestions?
 
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guessing it probably has to pair with a circuit that monitors the ALC circuit voltage to mute and un-mute the thing between stations.
 
What board? A board with a LA3401 on it so we need a schematic of the LA3401 circuits and the rest of the tuner since the muting is determined by the FM detector such as a LA1235 and associated circuitry. Muting is done by detecting IF level and deviation from center
Refer to other tuners that uses the same part, iirc I have a couple of Yamaha tuners using that part, rx-900u and a tx-1030?
 
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