SONY XR5800RDS TECHN
Manual de Servicio

RV115 is the Volume control, note its somewhat unusual connection to obtain a Volume boost during a Traffic Announcement (TA). One side of the variable resistor is connected to ground via RV322 and Q323. During normal reception Q323 is closed, so RV115 is grounded and RV322 has no effect. When receiving a Traffic Announcement Q323 will open because of the R ON switching signal and RV115 looses its reference to ground. As a result the Volume will rise and RV115 will have only a small influence on the output level. RV322 determines the Volume Preset Level. Note that during TA RV321 (Balance control) also has no effect on the output level. Figure 4.3 shows the line amplifier and part of the Fader circuit. Q401 and Q421 are part of the muting circuit controlled by IC701. The Fader Select switch is used to make fading possible between the line outputs and the front power outputs. This allows an external power amplifier, driving the rear speakers, to be connected to the line outputs while the built-in power amplifier drives the front speakers.

Fig. 4.3. Line Amp and Fader Circuit

The built-in power amplifier is shown in figure 4.4. It is built around IC341 (TA8221H), a power amplifier IC with overload, thermal and short circuit protection. The power supply pins (pin 10 and 17) are always connected to the accessory lead, regardless of the power supply switch. IC341 is in standby mode as long as the voltage on pin 4 is less than 2 volt. When power is switched on, the voltage on pin 4 rises to approximately 4 volt and the power amplifier switches itself on. This causes a soft start, thereby avoiding clicks in the speakers during power on. Beep pulses from IC701 are added to the music signals via the inverting inputs of the PRE-AMP. The volume setting has no effect on the level of the beeps because they are added directly to the power amplifier. The outputs of IC341 pass RV620 and RV621 (50 ohm, wirewound resistor) for Fader control before going to the speaker outputs. � 12 �