Kenwood TK-885 Service Manual
Also see for TK-885: Instruction manualService manual
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17TK-885CIRCUIT DESCRIPTION PA SwitchIf the optional KAP-1 is used, the PA (Public Address)function becomes available. In this case, the signal flowchanges as follows;“PA2” Q507 SW.A SW.B SW.D Public addressL L L H H OFFH H H L L ONPower Supply CircuitWhen the POWER switch on the control unit is pressed,the PSW signal goes low. This signal is inverted by Q26 andsent to a flip-flop IC (IC15). This IC outputs a control signalwhen the PSW goes low. When the power turns on, pin 1 ofIC15 outputs a low signal and Q30 turns on. The base ofQ28 goes high, Q28 turns on, SB SW (Q27) turns on andpower (SB) is supplied to the set.This circuit has an over-voltage protection circuit. If a DCvoltage of 20V or higher is applied to the power cable, D34turns on and a voltage is applied to the base of Q31. Thisvoltage turns Q31 on and turns Q28 and SBSW off. Thiscircuit has a TIMED POWER OFF (TOF) function which canbe programmed by software.It is controlled through pin 6 of IC7. When the TOF linegoes high, Q22 turns on and then Q25 turns on. Pin 6 ofIC15 goes high, then pin 1 goes high to turn Q27 off. D/A ConverterThe D/A converter (IC5) is used to adjust TONE and MOmodulation, beep, AF volume, TV voltage, FC reference volt-age, and PC POWER CONTROL voltage level.Adjustment values are sent from the CPU as serial data.The D/A converter has a resolution of 256 and the followingrelationship is valid:D/A output = (Vin – VDAref) / 256 x n + VDArefVin: Analog inputVDAref: D/A reference voltagen: Serial data value from the microprocessor (CPU) Horn ControlThe horn switch, consisting of Q4, Q5, and Q6, controlsthe horn relay. It is supplied by the dealer to provide theexternal horn alert function.Q5 disables horn alert, turning on when its base is high,to inhibit the function. Normally, the output from IC7 is low,and Q6 is off; the base of Q4 is about 0V and Q4 is off.When horn alert is enabled, the output from IC7 goes highand Q6 turns on. The base current flows through R58 to Q4to turn Q4 on. Q4 can sink a maximum of 100mA. If theoperational KAP-1 is used, it can drive up to 2A.8C HORD7Q4Q6R58Q5R2 R50R152+BIC7ShiftregisterHNCIGNFig. 14 Horn controlSW.DSW.BSW.ATXOUTMSKGSRXINIC504AudioprocessorRXOUTIC506AnalogSWMO47KQ5075C“PA2”Fig. 15 PA switchQ27SWQ28SWQ30SW Q25SWQ22SWQ26INV.IC15F.F.Q31SWD34SWR152R151IGNSB +BPSWTOFIC76pinFig. 16 Power supply circuit |
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