Kenwood TK-885 Service Manual
Also see for TK-885: Instruction manualService manual
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Contents
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15TK-885 Power Amplifier CircuitThe transmit output signal from the VCO is amplified to aspecified level of the power module (IC400) by the driveblock (Q202, Q204, Q205). The amplified signal passesthrough the transmission/reception selection diode (D209)and goes to a low-pass filter. The low-pass filter removesunwanted high-frequency harmonic components, and theresulting signal is goes the antenna terminal. APC CircuitThe automatic transmission power control (APC) circuitdetects part of a power module output with a diode (D27,D30) and applies a voltage to Q21. Q21 compares the APCcontrol voltage (PC) generated by the D/A converter (IC5)and DC amplifier (IC6) with the detection output voltage tocontrol Q19 and Q20, generates DB voltage from B voltage,and stabilizes transmission output.Q17 turns the PC signal on or off using 8T so that thecircuit works only during transmission. With stability at lowpower in mind, Q29 turns off to optimize the detection volt-age.The APC circuit is configured to protect overcurrent ofthe power module due to fluctuations of the load at the an-tenna end and to stabilize transmission output at voltageand temperature variations.CIRCUIT DESCRIPTIONControl CircuitThe CPU carries out the following tasks:1) Controls the shift register (IC7, IC8, IC508) AF MUTE, T/RKEY outputs.2) Adjusts the AF signal level of the audio processor (IC504)and turns the filter select compounder on or off.3) Controls the DTMF decoder (IC507).4) Controls the LCD assembly display data.5) Controls the PLL (IC300).6) Controls the D/A converter (IC5) and adjusts the volume,modulation and transmission power.RFAMPQ202,204RFAMPQ205POWERAMPIC400APCDRIVERQ19DB+BVR1Q20PRIDRIVERDCAMPIC6PCSWQ17ANTSWD209LPFANTQ29POWERDETD27,30Q21APCCONTROLH/LSWH/LIC7 5pin25W (High power): "H"8T(TX : 8V)TX :PC SW OND15PCIC523pinFig. 7 APC circuitIC5D/AconverterIC300PLLIC7ShiftregisterIC8ShiftregisterIC508ShiftregisterDTRFCLKES2ENOECSCKDTACKSDCPEPAFCLRAFMSKEAFDATAFRDTAFTRDAFRTMAFSTBIC504AudioprocessorIC507DTMFDECO.IC511CPUTX-RX UNITLCD ASSYFig. 8 Control circuit Memory CircuitMemory circuit consists of the CPU (IC511) and a flashmemory (IC510). A flash memory has a capacity of 2M bits(256k x 8) and contains the transceiver control program forthe CPU and the data for operating features.This program can be easily downloaded from an externaldevice. The CPU (IC511) controls the flash memory throughan external address bus and an external data bus. The CPUcontrols the EEPROM (IC512) through two serial data lines.• Flash MemoryNote: The flash memory stores the data containing theFPU (KPG-62D) program, Security Number (MPT SerialNumber), and firmware program (User mode, Test mode,Tuning mode, etc.).This data must be reinstalled when replacing the flashmemory.• EEPROMNote: The EEPROM stores tuning data (Deviation,Squelch, etc.).Realign the transceiver after replacing the EEPROM.SCLSDAIC511CPUADDRESS BUSDATA BUSIC510FLASHMEMORYIC512EEPROMFig. 9 Memory circuit |
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