Kenwood KRC-646D Service Manual

KRC-646D/CIRCUIT DESCRIPTIONDescription of ComponentsTUNER UNIT (X05-3182-70, -72)Use/Function Operation/condition/compatibilityFM IF DetectionNoise CancellerMPXLOCAL/DX SwiF GainANRC Buff.CRSC DriverSYNTHESIZER UNIT (X14-2062-7X)Component Use/FunctionKRC-G46L: -70, -72 KRC-646D: -71IC1 PLL synthesizer & microprocessorOperation/Condition/Compatibility1C2(1/6) Inverter gate L: MONO/STEREO switch control.D: Band switch inhibition circuit in SDK mode during TAPE operation,1C2(2/6 3/6) Inverter gate1C2(4/6) tnverter gate tion circuit from. the cassette mechanism in RADIO mode.Mute OFF time delay circuit of IC1 MUTE output. _Mute drive output of TAPE equalizer output stage and MUTE signal inhibi-1C2(5/6) !nverter gate AM + B switch control.1C2(6/6) Inverter gate MW/LW select, and LW PLL LPF select switch.1€3(1/4) AND gate LO/DX select switch. so een i =1C3(2/4) AND gate1C€3(3/4)1C3(4/4)1C4(1/4)L: TAPE/RADIO select switch.D: In SDK mode during TAPE operation, this also becomes TAPE/BANDselect switch by DK interruption.AND gateAND gateAND gate (IC1 Key matrix)1C4(2/4)1C4(3/4)AND gate (IC1 Key matrix)=L: MONO key, D: DK ON/OFF switch,MW/LW selectselect control and FM/MW PLL |LPF select switch.SK key input. “H”: No SK input,’ “LY: : SK input isPresent.AND gate (IC1 Key matrix) ST key input, SHES : No ST input, nod sae:eu input is present.1C4(4/4)1C5(1/4)__ AND gate (C1 Key matrix) SD key input. OHM: ; ‘No SD input, Tee: SD input is present.AND gate (IC1 Key matrix) FWD/REV key input. “HH Reverse, "L” : Forward.1C5(2/4) AND gateL: Dolby key.D: SK ON/OFF switch. In SDK mode, Seek when DK is OFF. SK is OFFwhen lower than stop level, and ON when more than that.1C5(3/4) AND gate D only : In SDK mode during TAPE operation, BAND switch inhibition circuit.1C5(4/4) AND gate Dolby ON/OFF switch.1C6,1C7 BTL Power amp.Q1i~Q3 +9V AVR (TUNER + 9V) - + SV constant voltage power supply ffor TUNER circuit.Q4,05 + 9V AVR (AUDIO + 9V) +9V constant voltage power supply for AUDIO circuit.O6 +5.6V AVR + 5V constant voltage power supply for 1C1 and other logic circuit,Q7,Q8 FM + BSW_ In FM mode, turns ON and supplies the Power to FM circuit via TUNER + OV.Q9 ,Q10 AM + B SWQ11,Q012 _ 1C1 CE controlIn AM mode, turns ON and supplies the ‘power to AM circuit via TUNER +9V,When power switch is turned ON, transmits tthe “SHAY signal to 1Cl CE pin.Q13 __Mute driveQ14 Mute driveWhen power switch is turned OFF (ACC is OFF), drives the Mute circuit.Drives the Mute control signal of IC1.Q15 Mute drive Drives the Mute circuit when ejecting the tape.Q16 Mechanism Mute inhibition circuitQ17,018 Motor driveaig ‘AM +B Sw control —_ =| InTAPE mode, turns AM + B switch OFF.Q20 ,Q22,024 MONO display inhibition circuit in AM mode :Inhibits the Mechanism- ‘Mute inRADIO mode.L: Drives the motor in TAPE mode, and releases the head when power is turnedOFF.D: in SDK mode during TAPE operation, releases the head when interruptedby DK.;_L only: In AM mode, applies IC1 cOM2 output to both ends of MONO LCD.Q21 023,025 Enables the MONO display in FM mode In FM mode, makes LCD2 of IC1 connect to LCD pin of MONO LCD,__and enables to light the MONO LCD when MONO is selected.L only:FM/MW PLL LPF inhibition switch When LW is selected, shunts the PLL LPF input for FM/MW and inhibits itsoperation.