Kenwood TS-990S Service Manual

Also see for SP-990: Instruction manual

Contents

TS-990S28CIRCUIT DESCRIPTION5-4. Transmit Power ControlTransmit power control is done the same way as in previ-ous models; the ALC circuit controls the ALC voltage usingthe progressive wave voltage (VSF) and keeps a constantoutput.The voltage detected by the VSF/VSR detection circuit(a circuit for the detection of progressive and reflection wavevoltages) in the antenna switch unit (X53-441 A/2) is sent toCN3 of the TX-RX unit (X57-827 A/2). The progressive wavevoltage is divided into a suitable voltage by the resistance,and applied to the differential amplifi ers consisting of IC801.The output voltage of IC801 (1/2) rises along with a risein progressive wave voltage while the base current of Q802increases and the collector voltage, for which the ALC timeconstant CR is selected, goes down. The output voltage ofthe buffer (IC801 2/2) goes down along with a fall in collectorvoltage. The resistance-distributed ALC voltage then goesdown. If the ALC voltage (2.5 V when the ALC is inactive)goes down, the IF amplifier’s (Q706) second gate voltagegoes down and the gain is decreased.When transmitting AM, Q801 is turned on approximately50 ms after transmission, and the ALC voltage is controlledby averaging the progressive wave voltage. The input voltageinto pin 2 of IC801 (1/2), which will be the ALC’s referencevoltage, is controlled by the adjustment value (POC) fromthe main MCU, and sent from pin 5 of the D/A converter(IC55).SWR protection is controlled by the reflection wave volt-age. The reflection wave voltage is divided by the resistanceand applied to IC802 (1/2). If it exceeds a specified volt-age, the output of IC802 (1/2) increases the base current ofQ803, which performs ALC voltage control, thus loweringthe gain and power.ID protection is under the control of the ID voltage detect-ed in the final circuit. The ID voltage is applied to IC802 (2/2).If it exceeds a specified voltage, the output of IC802 (2/2)controls the ALC voltage and lowers the gain and power.The PWR (power) meter is amplified from the progressivewave voltage, the SWR meter is amplified from the reflectionwave voltage, and the ALC meter is amplified from the ALCvoltage by the relevant operation amplifier, and they are ap-plied to the ADC for meter-indication.The VD meter indicates a divided drain voltage of thefinal circuit read by the A/D converter circuitry. The TEMPmeter for temperature protection uses the A/D convertercircuitry to read and display the voltages of the respectivethermistors (X45-388 A/2 TH1 and TH2) on the push-pullFETs of the final circuit and performs the three-stage (low-, medium-, and high-speed) fan control of the fi nal unit andtwo-stage (low- and high-speed) fan control of the AT unit.If an abnormally high temperature occurs, the transceiverlowers the transmit power to 5 W and displays a warningmessage. If the temperature still rises, the transceiver stopstransmission and displays an error message.The main screen displays each meter selected. Further-more, the signals of meters selected in the configurationmenu can be sent out as MMET and SMET signals to ex-ternal meters through the METER terminal and ACC2 ter-minal. These signals are sent out from the D/A converter inthe main MCU, and IC101 in the TX-RX unit (X57-827 A/2)6. Scope Circuit6-1. From the IF Input Stage to the IF Amplifier(SCIF1_AMP)The input signal into the scope circuit is an IF signal ob-tained from the RX unit or the TX-RX unit, the frequency ofwhich is SC08M at the time of the main signal reception andis set to SC11S or SC73S which varies with the receptionband at the time of the sub signal reception. And the scopedisplay is available at the time of signal transmission, the fre-quency of which uses SC73S obtained from the TX-RX unit.When SC08M and SC11S are selected, the signal isamplified by the input buffer amplifier (Q7 and Q8). Theimpedance is converted in L7 and L8 and sent to the nextstage via the diode switchers (D2 and D3). When SC73S isselected, the input is amplified by the input buffer amplifier(Q12) and sent to the next stage (SCIF1_BPF) via the diodeswitcher (D4). SC73S does not pass along the 1st Mixer.In the 1st mixer (SCMIX1), the signal is up converted bySCLO1 (main: 61.721MHz/sub: 64.847MHz), and convertedto the 1st IF (SCIF1: 73.095MHz) for scope use. The SCIFIsignal passes through the BPF for the elimination of imageinterference, and is sent to the IF amplifier (SCIF1_AMP)via the attenuator. The attenuator provides three levels of at-tenuation, -10 dB, -20 dB and -30 dB.6-2. From the 2nd Mixer (SCMIX2) to the 3rd Mixer(SCMIX3) InputThe SCIF1 is applied to the diode-employed DBM (2ndmixer) and converted to the 2nd IF (SCIF2 at 10.7MHz). Thebalanced-unbalanced conversion of the 2nd IF signal is per-formed in L73 and transmitted to the MCF (XF1) on the nextstage. The output signal from the MCF is amplified by theSCIF2_AMP and sent to the SCMIX3 (3rd mixer).Fig. 29 Transmit power controlmakes level changes in the signals.Q706ALCTX IF AMP (ALC)VSFPOCAMBALCPOWERCONTROLVSWRPROTECTIDPROTECTVSRPROIDQ803IC802EXT ALCIC801(1/2)Q802IC801(2/2)IC802