Kenwood TS-950S Service Manual

Also see for TS-950S Digital: Instruction manual Instruction manual Instruction manual Instruction manual Service manual

lO-JOUS/OVCIRCUIT DESCRIPTIONThe speech processor can be turned on and off onlyin the SSB mode. !n FSK, the processor is automati-cally switched into the circuit. When the speech proc-essor is on, the SSB signal obtained from the output ofQ26 is amplified by Q33 (2SC2712}, and the compo-nents above a specific level are clipped. The resultingsignal is amplified by Q30 (3SK131). The output levelof the speech processor is varied by changing thesecond gate voltage on Q30. The output level iscontrolled by the PROC OUT control on switch unit (A)(H/10). The processor output from Q30 passes throughceramic filter CF5, and is output when processor Q25is turned off by D60, D61, and D62 (RLS73x3}. Thesignal then exits the signal unit.The signal supplied from the signal unit enters theIF unit and is mixed with the third local oscillator signalof 9.285 MHz by Q41 (3SK131) to obtain an 8.83-MHzIF signal. This signal passes through ceramic filter CF1with the NULL point set at 9.285 MHz, amplifier Q40(2SC2712) for matching the signal to the next ceramicfilter XF3 (YK-88S), and the 8.83-MHz IF filter. TheSSB, FM, FSK signals passe through XF3 (YK-885), andthe CW and AM signals pass though the filter unit (C/3). The output from the filter is amplified by O38(3SK131). ALC is applied to 38.The output from Q38 is mixed with the second localoscillator signal of 64.22-MHz in Q36 ‘and Q37(3SK131x2) to generate a 73.05-MHz signal. This sig-nal enters the RF unit.from the IF unit.In the RF unit, the signal passes through three LCbandpass filters, L93, L94, and L95, is mixed with thefirst local oscillator signal in Q20 and Q21 (3SK131x2),and is converted to the target transmit frequency. Theoutput of Q20 and Q21 passes through a bandpassfilter, which is split to three frequency ranges (7.5MHz, 7.5 to 14.5 MHz, 14.5 to 30 MHz; the 7.5 MHzsection covers all frequency below 7.5 MHz}, amplifiedby Q22 (3SK131) and Q19 (2SK2954), and routed fromthe DRIVE OUT terminal on the rear panel. The signa!enters the final unit via the DRIVE IN terminal throughthe jumper cable at the rear.The signal is amplified by Q1 (2SC1971), Q2 and Q3(28C3133x2), Q4 (1/2, 2/2) (MRF429MP). Harmonicsare eliminated from the signal by the filter unit, and thesignal is emitted from the antenna.FSK is based upon AFSK methods with the mark(2125 Hz) or space (2295 Hz) being generated by thecarrier unit or the AFSK signal is input to signal unit iC9and modulated by D41. In the FSK mode, the speechprocessor circuit works, providing 10- to 20-dB ofcompression, and also suppresses the difference inthe levels between the mark and space signals.The FM signal passes through buffer amplifier Q20(25C2712) and the FM MiC AMP module in the AFunit, and is used to modulate the second local oscilla-tor.¢ ALC circuitThe level of the forward wave voitage (VSF) de-tected in the filter unit may be adjusted by VR12 (VSF)on the contro! unit and is applied to the differentialamplifier composed of Q10 and Q11 (25C2712x2).When VSF is applied to the base of Q10, the emittervoltages of Q10 and Q11 increase and the currentthrough the base of Q11 decrease which causes thecollector voltage of Q11 to rise. When this voltageexceeds the emitter voltage of Q1 (2SC2712) (about1.8 V; stabilized by D1 [LT8001P]), the current beginsto flow thru the base of Q1, dropping the on the collec-tor. The ALC time constant RC circuit is connected tothis collector. The change in the collector voltage isshifted by approximately 2.7 V by Q4 (2SK208} and DS(RLZJ4.7B), and matched with the voitage for keyingby Q5 (2SC2712) and D6 (RLS73) to generate the ALCvoltage. This ALC voltage activates the ALC by lower-ing the second gate voltage of Q38 (3SK131) of the IFunit.+ Power control circuitPower is controlled (reduced) by lowering the basevoltage of Q11. As the base voltage of Q11 is de-creased, the emitter voltages of Q10 and Q11 aredecreased. This allows Q10 to be turned on even ifthe base voltage (VSF} of Q11 is low. That is, ALCworks to lower the power even if the power is allreadyrelatively low.When the power output is maximum, Q16(DTC124EK} is on, Q12 and Q14 (DTC124EKx2} areoff, and VR2 (PWR VR) of the switch unit (A) (H/10) isshorted. Therefore, the base voltage of Q11 has thevalue determined by voltage dividers R66, R67, andfront panel PWR VR. When the PWR VR is turned toMIN, the base voltage of Q11 is lowered, and ALCbegins with low power. When the PWR VF is set toMIN, VR10 (MIN) and the PWR VR of the control unitare parallel, and the MIN power setting can controlledby VR10.For AT tuning, the power is lowered to about 10 W.The AT start signa! {ATS} turns on Q14, and the base ofQ11 is connected to ground via R72 to lower thepower.Q15 (DTC124EK) is used to turn off the PWR VRcontrol to prevent the PWR VR from influencing tun-ing.FOR SERVICE MANUALSCONTACT:MAURITRON TECHNICAL SERVICESwww. mauritron.co.ukTEL: 01844 - 351694FAX: 01844 - 35255419