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开机图像正常,无伴音但有噪声,说明伴音功放部分基本正常,该机伴音为双制式电路,即中国制式6.5MHz与香港制式6.0MHz。伴音信号通过IC101(TA7680AP)的(15)脚经C123(47pF)耦合,通过D122及D123的导通与截止来进入伴音中放电流IC101(21)脚内部的。由于D122及D123的导通与截止是通过外界施加电压来完成控制的。当把伴音制式开关拨至中国制式挡位时,+12V电压通过R122把D122导通,伴音信号随之通过,此时+12V电压通过R123把D123也截止,使伴音信号不能通过。当把伴音制式开关拨至香港制式时,+50V电压通过R126使D123导通,伴音信号随之通过,+50V电压也使D122截止。
Boot image is normal, no sound but noisy, indicating part of the sound amplifier basic normal, the machine sound dual system circuit, that is, the Chinese standard 6.5MHz and Hong Kong standard 6.0MHz. The audio signal goes through the C123 (47pF) pin of IC101 (TA7680AP) through C123 (47pF), and enters the internal discharge current of IC101 (21) via the on and off of D122 and D123. As D122 and D123 on and off by the external voltage to complete the control. When the sound system switch to the Chinese standard gear, +12 V voltage through R122 to D122 conduction, accompanied by sound signals, this time +12 V voltage through R123 to D123 also cut off, so that the sound signal can not pass. When the sound system switch to the Hong Kong standard, +50 V voltage through R126 so that D123 conduction, accompanied by sound signals, +50 V voltage also makes D122 cut-off.