Kenwood TK-880 Service Manual

Also see for TK-880 series: Programming instructions Instruction manual Instruction manual Instruction manual Instruction manual

29TK-880 Display CircuitThe CPU (IC511) controls the shift register (IC508) anddisplay LEDs. When the LG line goes high when the trans-ceiver is busy, Q508 turns on and the green LED on D511lights. In transmit mode, the LR line goes high, Q509 turnson and the red light lights. Backlighting LEDs for the keyoperation unit (D512~D517) and LCD are provided.When the KBLC line goes high, Q512 turns on, thenQ513 turns on, and the key illumination LED lights. A volt-age is applied to the LEDA line to turn on the LCD backlight. Key Matrix CircuitThe TK-880 front panel has ten keys. Each of them isconnected to a cross point of a matrix of the KEY1 to KEY7ports of the microprocessor. The KEY5 to KEY7 ports arealways high, while the KEY1 to KEY4 ports are always low.The microprocessor monitors the status of the KEY1 toKEY7 ports. If the state of one of the ports changes, themicroprocessor assumes that the key at the matrix pointcorresponding to that port has been pressed. Unusedpoints (KEY1 to KEY7) are also used for foot switch (FSW)input.Q512SWQ508SWQ509SWQ513SWKBLCLGLRIC508ShiftregisterD511GRNREDD512~517LEDAFig. 11 Display circuitMO is summed with the external pin DI line by the sum-ming amplifier (IC3) and the resulting signal goes to the D/Aconverter (IC5). The D/A converter (IC5) adjusts the MOlevel and the balance between the MO and TO levels. Partof a TO signal is summed with an output signal from pin 3(MO) of IC5 and the resulting signal goes to the MD pin ofthe VCO. This signal is applied to a varicap diode in the VCOfor direct FM modulation.IC511CPUKEY7KEY6KEY5KEY4KEY3KEY2KEY1MONI AD CALL CHDOWN CHUPB CVOLUP VOLDOWNFSWQ511Fig. 12 Key matrix circuit EncodeThe QT, DQT signals are output from LSDO of the CPU(IC511) and go to the D/A converter (IC5) of the TX-RX unit(A/2). The DTMF and single/5-tone signals are output fromHSDO of the CPU and goes to the audio processor (IC504).An MSK signal is output from the audio processor accordingto the data (AFDAT) from the CPU. The signal is summedwith a MIC/MSK signal by the audio processor (IC504), andthe resulting signal passes through an analog switch (IC506)and goes to the TX-RX unit (A/2) (MO).X1VCXOIC5D/AA1VCOIC3SUMAMPIC506AnalogSWIC504AudioprocessorIC300PLLMBMDMOTOHTDIMICTX-RX UNIT (A/2)AFDATLSDOHSDOIC511CPU DecodeThe signal (DEO) detected by the TX-RX unit (A/2) passesthrough two low-pass filters of IC501, goes to LSDI of theCPU (IC511) to decode QT, DQT. The DTMF signal is de-coded by a dedicated IC (IC507) and the resulting signal issent to the CPU (IC511) as serial data (STD).The 5-tone signal passes through high-pass filter, IC504and then through low-pass filter, IC710. After passingthrough these filters, only the audio signal between 300Hzand 3kHz is extracted and input to comparator, IC502. Thecomparator converts the input signal into a square wave-form (0 and 5V). This square waveform is then fed to theHSDI line of CPU (IC511).IC511CPUIC501(2/2)LPFIC501(1/2)LPFIC710LPFIC502ComparatorIC504HPFLSDIIC507DTMFDECO.STDHSDIDEO 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)CIRCUIT DESCRIPTIONFig. 13 EncodeFig. 14 Decode