Marantz 2015 - Phono and Pre-amplifier; Main Amplifier; Audio Trouble Analysis

When no reading is obtained in the meter, check FM local oscillator circuit, using a 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, next check all voltage
distribution in the FM Front End and IF amplifier unit and compare them with those shown in
the circuit diagram. When signal strength meter deflects but no sound is obtained, check audio
circuits, using high sensitive oscilloscope.
3.3.2 Symptom: No Stereo Separation
First check the “MONO” switch is in normal out position. Connect a FM RF signal generator
output modulated by a stereo modulator to the rear FM antenna terminals, and check the stereo
beacon is turned on or not. If not turned on, check for 19 KHz pilot signal and 38 KHz switching
signal, using an oscilloscope.
4. Phono and Pre-amplifier
Signals from the tuner and AUX jacks are applied to the selector switch. Signals from the
PHONO jacks are applied to the phono-amplifier consisting of transistor H301 and H303. The
gain of the amplifier is 37 dB. The amplified and equalized phono-signals are, then, fed to other
section of the selector switch which, in turn, applies output signals from the tuner,
phono-amplifier and AUX jacks to the TAPE MONITOR switch and TAPE OUT jacks. The TAPE
MONITOR switch applies the signals to the balance and volume controls.
The controlled signals are fed to the pre-amplifier consisting of H501. Frequency response of
the amplifier can be varied by BASS and TREBLE controls. The controlled output are then led
to the main amplifier.
5, Main Amplifier
Transistor H601 is a pre-driver coupled to the transistor H603 through capacitor C611.
Transistor H603 drives the inverter transistors H615 and H617 which, in turn, drive the power
stage consisting of HOO1 and HOO2. Transistors H611 and H613 are current limitters and operate
as power protecting circuits.
Excessive currents flowing into the power stage are detected by the resistors R645 and R650
and the resultant variations are applied to the transistors H611 and H613 and make them turned
on. This decreases the current flowing into the H615 and H617. In this way the currents flowing
in the power stage (HOO1 and HOO2) are restricted within a safe value.
6. Audio Trouble Analysis
1. Excessive line consumption a. Check for shorted rectifiers H802, H803, H804, H805,
H806 and H807.
b. Check for shorted transistors HOO01, HOO2. Check LOO2
for short.
2, No line consumption or zero bias. a. Check line cord, fuse, shorted H701, H702, H605 and
H606.
b. Check for open rectifiers H802, H803, H804, H805,
H806 and H807 or open L002.
3. High hum and noise level. Check filter capacitors C004, C601 and C602.
4. Parastic oscillation a. Check for defective capacitors, C607, C608, C613,
; C614, C617 and C618.
5. Improper clipping a. Check for proper adjustment of R615 and R616.
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