Kenwood TS-950S Service Manual

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TS-950S/SDCIRCUIT DESCRIPTION« Side tone generation circuitThe AFT signal (80 KHz when the PITCH control is atthe center; the frequency is changed within +50 kHzby turning the control; 150 kHz in the SSB mode) gen-erated by the CAR unit is rectified by Q1. The squarewave of 800+500 Hz divided to 1/100 by IC1 is appliedto switched capacitor filter IC3 to obtain a sine waveinterlocked with the CW receive pitch.The 40425 kHz obtained by dividing the AFT signain halft with IC1 is sent to the clock that determines800 t SOOHZthe center frequency of IC3.Keying the transceiver switches Q7 via the KEY linefrom the control unit (high when the key is down). Thisforward biases muting transistor Q6 to produce theintermittent sine waves.When the monitor is on, Q6 is biased through R27and side tone is turned off.FOR SERVICE MANUALSCONTACT:MAURITRON TECHNICAL SERVISO 25Ktu www. mauritron.co.ukLoreSN74LS390NSTEL: 01844 - 351694FAX: 01844 - 352554co80 +SOKHz(Cw MODE)1f12{t 10 R25ICG tard)IC8tav2) SIDE TONELEVELAF PA6Fig. 10 Side tone circuit+ AF VBT circuit (AF unit)Filter IC2 (MF1QCCWM) is inserted into the AF am-plifier circuit in order to eliminate radio interference.This circuit functions only in the CW mode when theAF TUNE switch is on.The center frequency of this filter is changed whenthe pitch of the receiver side tone is varied with thePITCH control. The Q of the filter circuit can be changedin conjunction with the AF VBT control.When SSBC or FSKC goes low in a mode other thanFM or AM, Q3 turns on via D3, and ICS (a/4) and (b/4)turn on. When CWB goes high in the CW mode, IC5(a/4) and (b/4) turn on via R20 and D1. (Preventing thesignal from passing through filter 1C2.)lf the AF TUNE button is pressed, AFTSW goeshigh, Q4 tuns on, and IC5 (a/4) and (b/4) turn off. SinceCWC is low, O5 turns on and ICS (c/4) and (d/4) turnon. The output of the filter circuit selected by IC2 iscontrolled by analog switch IC5 .The center frequency (fo) of the filter is 1/50 theclock frequency. 40425 kHz is obtained by rectifyingthe AFT signal of 80£50 kHz (in the CW mode) with Q1and dividing it in half with (C1. This signal is used asthe clock in the same way as with the side-tone gen-eration circuit, and fo is 8004500 Hz and is changed viathe PITCH control.The passband width can be varied with the AF VBTcontrol that is connected between pins 17 and 18 ofthe main receiver. The passband width can be variedwith potentiometer VR1 (10 kQ) in the sub receiver. Itcan be adjusted to within +100 Hz.Filter IC (MFIOCCWM)}, IC2, used here containstwo blocks consisting of an active filter (IC3 [MF5CWM}]used in the side tone circuit). Various additional filterconfigurations can be formed by using external resis-tors. The center frequency depends on the clockfrequency. The filter characteristics and clock fre-quency can be adjusted and set at will according to theratio of the external resistor values.CES23