Daewoo DV-K784N-JJ, Руководство по обслуживанию

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2) Audio circuit
1) Outline
This Audio Circuit use LA71004M A/V one chip IC of Sanyo's. The major feature of this IC is that has a Recording Bias current auto-
control circuit. So it is controlled by circuit automatically to keep consistent Recording current regardless change of head impedance.
Prior IC is used variable resistor to control Recording current passively.
But, variation range of HEAD Impedance has to be limited because of this auto-control circuit.
• R/P HEAD = 58 KOHM ± 15% (f = 70KHz)
• A/E HEAD = 34 OHM ± 20% (f = 70KHz)
¢¡
Serial Type
= 180 OHM ± 20% (f = 70KHz)
¢¡
Parallel Type
• FE HEAD = 80 OHM ± 15% (f = 70KHz)
It can be devided a parallel and a serial circuit by form of connection of AE Head & FE Head. In case of D/W, we adopt a serial-type
circuit.
2) Name and operation of pins in audio IC
!
Features
i) 1 chip type including PB amp, Line Amp, REC amp, ALC circuit, EQ switch Auto REC bias circuit.
ii) It is equipped with EQ switch which operates in SP/LP/EP modes respectively.
iii) ALC level is fixed on-6dBv.
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Function
Pin No Name Function
1 Auto-Bias-IN 320±10mVrms Input for auto-bias
2 EQ-SW2 Capacitor switch for head resonance in LP or EP SW ON
3 Auto-Bias-OUT DC control voltage for auto-bias
4 Auto-Bias Auto-Bias
5 EQ-IN Line input, Input impedance: 120k
Ω
6 EQ-NFB Negative Feedback of PB Amp
7 EQ-SW1 Playback equalizer switch in SP mode SW ON
8 EQ-OUT Playback Amp out
9 Line-BP-IN Line Amp input of playback Amp out
54 Mute ON/OFF Mute control
55 PB/EE PB/EE mode control
56 Audio REC/EE/PB REC/EE control
57 Line IN Line/Tuner input
58 ALC-DET Port for ALC filter (setup attact or recovery time)
59 Line OUT Line Amp out
60 REC IN Input to REC Amp
61 Vcc Vcc
62 Vref Filter Vref filter (Ripple filter)
63 GND GND
64 REC-OUT Recording Amp out