Marantz 2220 - Audio Circuitry and Analysis; Audio Trouble Analysis

3.3.2 Symptom: No Stereo Separation
First check the ‘““MONO” switch is in normal out position. Connect a FM-R 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 19KHz pile signal and 38KHz 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 H901, H903:and H905.
The gain of the amplifier is 40 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, H503 and H505.
Frequency response of the amplifier can be varied by BASS and TREBLE controls. The
controlled output are then led to the main amplifier through high and low pass filter
pushswitches. ~s
5. Main Amplifier
Transistor H701 is a pre-driver coupled to the transistor H703 through capacitor C711.
Transistor H703 drives the inverter transistors H709 and H710 which, in turn, drive the power
stage consisting of HOO1 and HOO2. Transistors H705 and H709 are current limitters and operate
as power protecting circuits.
Excessive currents flowing into the power stage are detected by the resistors R741 and R745 -
and the resultant variations are applied to the transistors H705 and H707 and make them turned
on. This decreases the current flowing into the H709 and H710. 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 HOO7, H804, H805.
b. Check for shorted transistors HOO1, HOO2, Check LOO2
for short.
2. No line consumption or zero bias. a. Check line cord, fuse; shortéd HO05, HOO6, H713 &
H7 14.
b. Check for open rectifiers HOO7, H804, H805 or open
LOoo2.
3. High hum and noise level. a. Check filter capacitors CO06, C703, & C704.
4. Parastic oscillation a. Check for defective capacitors, C705, C706, C713,
C714, C723 & C724.
5. Improper clipping a. Check for proper adjustment of 723 & 724.