Kenwood TS-990S Service Manual
Also see for SP-990: Instruction manual
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TS-990S21CIRCUIT DESCRIPTION4-4. From the 2nd IF to the SRIF outputIn FM mode, the signal is applied to the FM IC (IC602).In modes other than FM, the signal is input to the AM/SSB/CW/FSK/PSK mode mixer (D601 and D602) via D502.The FM mode signal is mixed with SLO3 (10.240MHz) inthe FM discriminator (IC602) and converted into the 3rd IF(455kHz). The 3rd IF signal passes through the ceramic fil-ters (CF602: wide, CF601: narrow), and is demodulated intoaudio signals and amplifi ed by the FM AF AMP (IC603).Signals other than in FM mode are mixed in the AM/SSB/CW/FSK/PSK mode mixer (D601 and D602) with theSLO3 (SRX-1 path: 11.398MHz, SRX-2 path: 10.719MHz),converted to the 3rd IF (24kHz), and amplified by the 3rd IFAMP (IC601).Signals in FM or other modes are sent from the SRIFconnector (CN600) on the TX-RX unit (X57-827 A/2) toCN670 on the DSP unit (X53-453).Fig. 19 From the 2nd IF to the SRIF outputIF input(10.695MHz/11.374MHz)IC602FM ICD502SwitchingFMCF602455k BPFBW: 12kHzCF601455k BPFBW: 9kHzIC603FM AF AMPAM/SSB/CW/FSK/PSKD601,602Sub RX 3rd MixerIC601Sub RX 3rd IF AMPIC604Multiplexer CN600SRIFTo DSP unit CN670(X53-453)4-5. 1st MixerThere are two 1st mixers used:SRX-1 path: IF frequency=11.374MHzSRX-2 path: IF frequency=73.095MHzThe 1st mixer for the SRX-1 path is a quad-balanced typemixer which consists of Q351 to Q354 (JFET), where thesignal is mixed with the SLO1 (12.495MHz to 32.195MHz) ata level of approximately 18 dBm and converted to the 1st IF(11.374MHz). Approximately 2.6V bias is added to the SLO1in order to suppress distortion.The 1st mixer for the SRX-2 path is a quad-balanced typemixer which consists of Q401 to Q404 (JFET), where thesignal is mixed with the SLO1 (73.120MHz to 133.095MHz)at a level of approximately 10 dBm and converted to the 1stIF (73.095MHz). No bias is applied to the SLO1.The variable resistor (VR401) in the 1st mixer are usedto adjust the mixer balance. If you have replaced the FETs(Q401 to Q404), transformers (L403, L404 and L406), vari-able resistors (VR401), or TX-RX unit (X57-827 A/2), do the1st mixer balance adjustment in adjustment mode.Fig. 20 1st mixer of the SRX-1 path+14V1st IF11.374MHzRF+2.6VSLO112.495~32.195MHzQ351Q352Q353Q354L356L359L357 |
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