Kenwood TK-3118 Service Manual

Also see for TK-3118: Service manual

16TK-3118TK-260 :K, K25) APCThe automatic power control (APC) circuit stabilizes thetransmitter output power at a predetermined level by sensingthe drain current of the final amplifier Field Effect Transistor(FET) . The voltage comparator, IC3 (2/2), compares thevoltage obtained from the above drain current with a referencevoltage which is set using the microprocessor. An APCvoltage proportional to the difference between the sensedvoltage and the reference voltage appears at the output of IC3(1/2). This output voltage controls the gate of the FET poweramplifier, which keeps the transmitter output power constant.The transmitter output power can be varied by themicroprocessor which in turn changes the reference voltageand hence, the output power.6) Terminal protection circuitWhen the thermistor (TH1) reaches about 80˚C, theprotection circuit turns on Q14 to protect transmitting finalamplifier (Q22) from the over heating.5. Power supplyThe battery power source is internally regulated by thecircuit (IC305) and outputs 3.5V DC (3.5M).This 3.5V DC (3.5M) is also supplied to the microprocessor(IC300) and reset IC (IC304).In the meantime, the microprocessor and switchingtransistor also generate a [3.5MS] reference voltage from thissource.This reference voltage is used for the following DC powersources:3.5V DC (3.5R for the receiver, 3.5C for both the receiverand transmitter) 5.0V DC (5R for the receiver, 5T for thetransmitter, and 5C for both the receiver and transmitter)6. Control systemThe microprocessor (IC300) is operating at a clock of 7.37MHz. The clock oscillator has an additional circuit to shift theoscillating frequency, using a switching transistor (Q303) toremove the internal beat interference that may be caused bythis oscillator. This microprocessor controls the LCD display,key operations, PLL data and other various functions.CIRCUIT DESCRIPTION / 电路说明5) 自动功率控制自动功率控制 (APC) 电路,通过测检末级放大器场效应管的集极电流来稳定发射的输出功率。电压比较电路, IC3 (2/2) 用微处理机设定的参考电压来比较从末级电流所获得的电压。自动功率控制电压与IC3 (1/2) 输出的自动检测电压和参考电压之间的差值成正比。此输出电压控制场效应管功率放大器，保持发射部输出功率常数。发射部输出功率可以通过微处理器进行改变，在微处理器中改变参考电压来控制输出功率。6) 温度保护电路当热敏电阻 (TH1) 的温度达到80℃时，保护电路开启Q14来保护末级放大器 (Q22) 避免过热。5.电源电池电源由电路 (IC305) 内部调整并输出3.5V直流。3 . 5 V 直流 ( 3 . 5 M ) 也提供到微处理器 ( I C 3 0 0 ) 和复位I C(IC304)。同时，微处理器和开关晶体管也从该电源生成 [3.5MS] 参考电压。该参考电压用于以下直流电源：3.5V直流 (3.5R用于接收，3.5C用于接收和发射) 5.0V直流(5R用于接收，5T用于发射，5C用于接收和发射)。6.控制系统微处理器 (IC300) 正在7.37MHz时钟下运行。时钟振荡器有其它电路转换振荡频率，并使用开关晶体管 (Q303) 来消除可能由该振荡器引起的内部拍频干扰。该微处理器控制L C D显示器、按钮操作、锁相环电路数据和其它各种功能。