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This DC output is furnished through LPF-2 to the trigger amplifier which drives the stereo
indicator lamp and stereo switch. Therefore, insufficient supply of the pilot signal results in
failure to light the stereo indicator and to turn on the stereo switch located in the path of the
38kHz switching signal, thereby avoiding a wrong stereo operation.
H303 fitted on the outside of pin (8) is a switching transistor for automatic monaural-stereo
switchover. When the intensity of an incoming signal from an FM station is weaker than a
predetermined level, this H303 is turned on and pin (8) is grounded, thereby developing a
condition for monaural reception. For a forced monaural operation, switch the MODE switch to
"MONO", and H303 comes into the "On" state with the positive bias voltage applied to the base,
and pin (8) is grounded, thereby establishing monaural operation. The transistor H302 connected
externally to pin (14) is intended to stop the 76kHz oscillation of the VCO which interferes an
AM signal during the reception of an AM station. When the function switch is set to "AM"
position, a positive bias is charged on the base of H302, H302 is turned on, and pin (14) is
grounded. Thus, the oscillation of the VCO is stopped, ending the interference with AM
reception.
3.3 SUGGESTION FOR TROUBLESHOOTING FM TUNER
3.3.1 SYMPTOM: NO FM RECEPTION
First turn the POWER switch on and try to tune FM stations. Rotate the flywheel-tuning
knob slowly and observe the FM signal strength meter. If the signal strength meter deflects at
several frequencies received, the tuner circuits preceding the discriminator circuit may have no
failure. When no reading is obtained in the meter, check the FM local oscillator circuit, using an
RF VTVM. The normal local oscillator voltage is one or two volts (rms) at the tuning capacitor,
depending on the tuning capacitor position. If the local oscillator voltage is normal, then check
all voltage distribution in the FM Front End and IF amplifier unit and compare them with those
shown in the circuit diagram. When the signal strength meter deflects but no sound is obtained,
check the audio circuit, using a high sensitive oscilloscope.
3.3.2 SYMPTOM: NO STEREO SEPARATION
First check that the "MODE" switch is in normal 2 CH position. Connect an FM RF signal
generator output modulated by a stereo modulator to the rear FM antenna terminals, and check
whether the stereo beacon is turned on or not. If not turned on, check for 19kHz VCO output
signal (J310), using an oscilloscope and frequency counter.
4. PHONO AMPLIFIER
Program source signals from the PHONO jacks on the rear panel are fed to the input circuit of
the Phono Amplifier through the selector switch, and the output of the Phono Amplifier is led to
another section of the selector switch. This amplifier provides a gain of 40dB.
5. BUFFER, TONE AND FILTER AMPLIFIERS
After passing through the FUNCTION switch (S001-2R, -4R) or TAPE MONITOR switch, all
signals are converted to low output impedance by the buffer amplifier. The signals, then, are
passed through the Dolby circuit, MODE switch and HI-BLEND switches and BALANCE and
VOLUME controls.
Signals properly attenuated by the VOLUME control are led to the tone amplifier and are
subjected to tone control by the BASS, MID and TREBLE controls, and high- and low-cut filter
amplifier circuits.
Thus controlled audio signals are then led to the PRE OUT jacks on the rear panel.
6. POWER AMPLIFIER
The signal from the tone filter amplifier is applied to the differential amplifier (base of H701)
through the coupling capacitor C701. The differential amplifier provides very high input
impedance, and its collector output (H702) is led to the base of H705 which in turn feeds its
output to the next stages: H706 through the network of R721, C710 and R728, and H707
Digitized in Heiloo Netherland
5/30/2017
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