Kenwood TS-950S Service Manual

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TS-950S/SD28CIRCUIT DESCRIPTIONTX to RX switchingWhen the standby switch is turned off, Q203 andQ202 of the CWT module (X59-3660-00) are turnedoff, and the SS signal changes from high to low. D16'sanode changes from high to low 5 ms after the SSsignal changes since there is a 5-ms time constantcircuit composed of R43, R44, and C37 attached to forthe output of pin 2 of 1C13.Therefore, the cathode of D15 CTXB switches fromtransmit to receive , and TXB goes low 5 ms after thestandby switch is turned off.When TXB goes low, Q154 of the TRX module (X59-3680-00) turns off, Q155 and Q157 turn on, and RXBrises,CKY downWhen SS goes low, pin 2 of IC6 goes low, pin 3goes high, pin 10 of IC5 goes low, and the CKY outputgoes low. Thus, the CKY signal changes from high tolow when the standby switch is turned off.The ALC waveform output from the ALC modulerises according to the time constant of the integrationcircuit.ALC | \RXB 5msFig. 17 CKY downFOR SERVICEMANUALSCONTACT:MAURITRON TECHNICAL SERVICESwww.mauritron.co.ukTEL:01844-351694FAX:01844-352554RBC generationWhen CTXB line changes from high to iow, pins 9and 11 of IC13 go low, and the NAND gate output atpin 4 changes from high to low 5 ms after CTXB goeslow; i.e., RXB rises according to the time constantcircuit provided ahead of pin 8 of the inverter output.The RBC signal is connected to the base of an NPNtransistor. This transistor switches the 455-kHz re-ceive IF circuit to ground. The receiver operates onlywhen RBC is low.Fig. 18 RBC generationPLL data and transmit/receive timing signalAs explained earlier, the SS signal is used at thebeginning of each operation. PLL data is switched,and diode switch and analog switch settings arechanged to assure stable transmission and reception10 ms after the SS line is grounded, until the last CKYtiming signal for transmit has been generated, and for5 ms after the RXB line rises, until the RBC line goeslow.2) Full break-in timingGeneration of the TXB signal at key downWhen the key is inserted into the key jack, pin 9 ofthe CWT module (X59-3660-00) is grounded, and theemitter of Q208 is grounded.When the key is down, 0201, 0208, Q206, andQ207 turn on, causing the output of pin 6, KYB, to gohigh. The KYB signal passes through D11, 023, pins 1and 2 of [C3, and D22, and forces the SS line high. Q7is turned on via D10, and the CSS line is grounded tonotify the microprocessor of the start of transmission.When the transmit disable signal TX! is low in orderto disable transmit, Q205 and Q204 of the CWT mod-ule (X59-3660-00) are turned on, and the CWB line isgrounded. Q206 and Q207 are turned off, and theKYB line goes low. The SS fine remains low during thisperiod. etWhen the SS line again becomes high, the CTXBline goes high via D16; therefore, Q153 and Q152 ofthe TRX module (X59-3680-00) are turned on in orderto generate the TXB signal. Meanwhile, Q154, Q155,and Q151 are turned off, and the RXB line switcheslow.