Marantz 2220B - Main Amplifier; Main Amplifier Circuit; Audio Trouble Analysis; Common Audio Faults

HEO7. Frequency response of the amplifier can be varied by BASS, MID and TREBLE controls.
The controlled output are then led to the main amplifier through high and low pass filter
pushswitches.
5. MAIN AMPLIFIER
Transistor H701 and H703 are a differential amplifier coupled to the transistor H70O7.
Transistor H707 drives the inverter transistors H721 and H723 which, in turn, drive the power
stage consisting of HOO1 and HOO2. Transistors H709 and H721 are current limitters and
operate as power protecting circuits.
Excessive currents flowing into the power stage are detected by the resistors R749 and
R747 and the resultant variations are applied to the transistors H709 and H711 and make them
turned on. This decreases the current flowing into the H721 and H723. 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 re}
. Check for shorted rectifiers H801, H802.
. Check for shorted transistors HOO1, HOO2, Check
LOOS for short.
a. Check line cord, fuse, shorted HOO5, HOO6, H725.
b. Check for open rectifiers H801, H802 or open LOOS5.
a
a
ion
2. No line consumption or zero bias
. Check filter capacitors C002, C004.
. Check for defective capacitors, C707, C708, C715,
C716.
5. Improper clipping a. Check for proper adjustment of R711, R712.
3. High hum and noise level
4. Parastic oscillation
Figure 1. Dial Stringing
Seininnectatclen