Kenwood TS-990S Service Manual
Also see for SP-990: Instruction manual
                                                                                                                                                                                                                                                    | |
TS-990S14CIRCUIT DESCRIPTION3-6. 1st MixerThe 1st mixer is of double balanced grounded switch typeincorporating the bus switch (IC7) and logic driver (IC8), andthe signal from the 1st mixer is mixed with the MLO1 (8.278to 51.752MHz) at a level of approximately +10 dBm and isconverted into the 1st IF (8.248MHz).A bias voltage of 2.5 V from the bus switch is applied toIC7 and a voltage of 2.5 V for duty ratio determination is ap-plied to IC8.Table 8 Preamplifier key displayFig. 11 Preamplifier 2 circuitScreendisplayCircuit operation Preampli-fier gainPostamplifierPreamplifiercircuit 1Preamplifiercircuit 2OFF OFF OFF 0dB OFFP.AMPON OFF 9dB ONOFF ON 22dB ONFig. 12 1st mixer circuitL55RF+2.5VIC7x4+2.5VMLO18.278~51.752MHzIC8L59L601st IF8.248MHz3-7. Noise Blanker Filter and IF Filter AdjustmentsFive types of filters (MCFs and crystal filters) are usedas a noise blanker fi lter and IF fi lters at a center frequencyof 8.248MHz. The noise blanker filter (XF1) and the IF filters(XF3, XF4, and XF8) with a passband width of 15kHz, 6kHz,and 2.7kHz need adjustments. The 500Hz and 270Hz IFfilters (XF5 and XF6) incorporate variable inductors, whichare precisely adjusted at the factory before shipping. Usersdo not need to adjust them. Adjust the IF filters first. Then,adjust the noise blanker fi lters.The IF filter (XF3) is a 2-pole MCF and its passbandwidth is 15kHz. Since the terminating impedance of the IFfilter (XF3) is 5.6 k, it is converted into 50 by the variableinductors (L94 and L97). Connect an appropriate equipment,such as a tracking generator, to the IF filter adjustment con-nectors (CN115 and CN129) and turn the variable inductors(L94 and L97) to adjust the IF filter. The IF filter (XF4) is a2-pole MCF, has a passband width of 6kHz and a terminat-ing impedance of 2.4 k. The IF filter (XF8) is a 2-pole MCF,has a passband width of 2.7kHz and a terminating imped-ance of 1.35 k. Perform the IF filter (XF4 and XF8) adjust-ment in the same manner as the XF3 adjustment. First, con-nect a tracking generator to CN115 and CN129, the turn thevariable inductors (L95, L98, L96, and L99) to adjust the IFfi lter.The noise blanker filter (XF1) is the same as the IF fil-ter (XF3) with a passband width of 15kHz. Adjustment ofthe noise blanker filter (XF1) will be carried out after thecompletion of the IF filter adjustment in adjustment modewith a passband width 15kHz IF filter connected. Connect atracking generator to the adjustment connectors (CN86 andCN129), and adjust the variable inductors (L110 and L111)on the noise blanker filter side. Do not adjust the variableinductors (L94 and L97) on the IF filter side when makingadjustments.If you have replaced the noise blanker filter, such as IFfilters (XF1, XF3, XF4, and XF8), variable inductors (L110,L111, L94, L97, L95, L98, L96, and L99), or the main RXunit (X55-313 A/2), be sure to perform MCF adjustments inadjustment mode.InputOutput14VQ2014V |
Related manuals for Kenwood SP-990
manualsdatabase
Your AI-powered manual search engine