Kenwood TK-885 Service Manual
Also see for TK-885: Instruction manualService manual
                                                    | |
Contents
|
16TK-885 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. 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.The DTMF and single tone signals are output from HSDO ofthe CPU and goes to the audio processor (IC504). An MSKsignal is output from the audio processor according to thedata (AFDAT) from the CPU. The signal is summed with aMIC/MSK signal by the audio processor (IC504), and the re-sulting signal passes through an analog switch (IC506) andgoes to the TX-RX unit (MO).MO 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.CIRCUIT DESCRIPTIONQ512SWQ508SWQ509SWQ513SWKBLCLGLRIC508ShiftregisterD511GRNREDD512~517LEDAFig. 10 Display circuit Key Matrix CircuitThe TK-885 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.IC511CPUKEY7KEY6KEY5KEY4KEY3KEY2KEY1(CLEAR) AD CALL SYSDOWN SYSUPB CVOLUP VOLDOWNFSWQ511Fig. 11 Key matrix circuitX1VCXOIC5D/AA1VCOIC3SUMAMPIC506AnalogSWIC504AudioprocessorIC300PLLMBMDMOTOHTDIMICTX-RX UNITAFDATLSDOHSDOIC511CPUFig. 12 Encode DecodeThe signal (DEO) detected by the TX-RX unit passesthrough two low-pass filters of IC501, goes to LSDI of theCPU (IC511) to decode QT, DQT.The MSK signal passes through IC504. IC504, includesband-pass filter and MSK decoder, converts the input signalinto a square waveform (0 and 5V). This square waveform isthen fed to AFRDT line of CPU (IC511).IC511CPUIC501(2/2)LPFIC501(1/2)LPFLSDIIC507DTMFDECO.STDAFRDTDEOIC504AUDIOPROC.Fig. 13 Decode |
Related manuals for Kenwood TK-885
This manual is suitable for:
manualsdatabase
Your AI-powered manual search engine