Service Notes - Marantz 2270 Manual

INTRODUCTION
This service manual was prepared for use by Authorized Warranty Stations and contains service
information for Marantz Model 2270 Stereophonic Receiver.
Servicing information and voltage data included in this manual are intended for use by the
knowledgeable and experienced technician only. All instruction should be read carefully. No
attempt should be made to proceed without a good understanding of the operation in the
receiver.
The parts list furnish information by which replacement part may be ordered from the
Marantz Company. A simple description is included for parts which can be usually be obtained
through local suppliers.
1. Service Notes
As can be seen from the circuit diagram the chassis of Model 2270 consists of the following
units. Each unit mounted on a printed circuit board is described within the square enclosed by a
bold dotted line on the circuit diagram.
1. FM Front End... 02... ec ee ee eee eee mounted on P.C. Board P100
2. FM IF Amplifier... 0.0.0... cc eee ce eee eee eee mounted on P.C. Board P200
Si FM Detector on aie ne Beh ee Sb ee ee eae SE eA mounted on P.C. Board P500
4. MPX Stereo Decoding Amplifier............ 00.0.0 eee aee mounted on P.C. Board P300
5. Muting Control Amplifier. ........ 0.0.0... 0 eee eee eee mounted on P.C. Board P550
G2 AM Tuner Uaits «cas seein G een Gea Geers wee eas mounted on P.C. Board P150
7. Phono: Amplifier... occas be ee ei eee eee eee ee es mounted on P.C. Board P700
8. Tone Amplifier... 2.0.0... cece ee ee eee mounted on P.C. Board P400
9. Tone Control Unit 2.0... ... ce ee eee mounted on P.C. Board P450
10. Power Amplifier .....0. 0.0... ccc cee eee ee eee eee mounted on P.C. Board P750
11. Regulated Power Supply and Protection Relay Circuit....... mounted on P.C. Board P800
12. Mono, High and Low Filter Switch unit .................. mounted on P.C. Board P600
13. Loudness, Muting and Speakers Switch unit .............. mounted on P.C. Board P650
2. AM Tuner
All components except Tuning capacitor and ferrite bar antenna are mounted on a printed
circuit board P 150.
The AM signals induced in a ferrite bar antenna are applied to the base of RF amplifier
transistor H151 through a capacitor of C151 and amplified to the level required for overcoming
the conversion noises, thus giving good S/N performance. The tuned circuits inserted in both
Out-and in-put circuit of the RF amplifier assure very high image and spurious rejection
performance. Thus amplified and selected AM signals are then applied to the base of converter
transistor H152 through a coupling capacitor C156. While the local oscillator voltage is injected
to the emitter of H152 through a capacitor C157. Both AM signals and oscillating voltage are
mixed at the base-emitter junction and converted into 455KHz intermediate frequency. The
resulting IF signal is applied to the first IF transformer L153 consisting of one ceramic filter and
two tuned circuits.
The output of L153 is led to the transistor H153 which in turn apply its output to the
transistor of next stage H154. The fully amplified IF output is then applied to the diode H157 to
detect audible signal through the detector transformer L154. The detected audio signal is filtered
and amplified and the final audio output is obtained from the collector of H155 and applied: one
to the tape out jacks through monitor switch on the front panel and the other to-the function
rotary switch.
The DC component of the detected IF signal is used as a AGC voltage to control emitter
current of H153 which in turn control the bias current of the RF amplifier through the resistor
R179 and R151. A part of IF signal output is also applied to the diode H158 through a capacitor
C167 and rectified to obtain DC current for energizing the AM signal strength meter M0071.