Marantz 4270 - Page 4

INTRODUCTION
This service manual was prepared for use by Authorized Warranty Stations and contains
service information for Marantz Model 4270 Stereo 2 + Quadradial 4.
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 4270 consists of follwoing
units. Each unit mounted on a printed circuit boards is described within the square enclosed by
a bold dotted line on the circuit diagram.
1. FMFrontEnd ..c.. cc. cece eee ee eee mounted on P. W. Board, P100
2. AM Tuner Assembly ...............++2+++++2 Mounted on P. W. Board, P150
3. FMIF Amplifier 2.2.0.0... 0.0... 0c. eee eee mounted on P. W. Board, P200
4. FM MPX Stereo Decoding ................0002 mounted on P. W. Board, P300
5. Phono Amplifier ........... 0.2.00 cece eee eee mounted on P. W. Board, P400
6. Vari-Matrix Unit ........ 0.0... ccc ee eee eee mounted on P. W. Board, P500
Te (DOWD Y Unit ace e8 0 003 66.06-35 8 8.048 heetedes Be bees mounted on P. W. Board, P600
8. Main Power Amplifier .......... 0.0.0.0 c cece ee mounted on P. W. Board, P700
9. Power Supply 6... eee ee ees mounted on P. W. Board, P800
10. FMCal, FM De-Emphasis .................... mounted on P. W. Board, PCO1
11. Tone Amplifier ......... 0. cece cee eee eee mounted on P. W. Board, PDO1
12. Buffer & Pre-Amplifier ................00000- mounted on P. W. Board, PEO1
13. Balance Control Unit ..............0 0c eee eee mounted on P. W. Board, PGO1
14. Hi-Filter, Loudness ............ 0c. cee ee eee mounted on P. W. Board, PHO1
15. Tone Control oo... cc eee eee mounted on P. W. Board, PJO1
16: 4Q0HZ TONG. e3 ed Hoo eee ae Baa wk ews mounted on P. W. Board, PLO1
17. B.T.L. Phase Inverter .......... 0.0.00 eee eee ee mounted on P. W. Board, PMO1
18. SP Protector Unit ........ 0... cece ee mounted on P. W. Board, PNO1
19} “Tape Mode: © aadidaditeeeevan wav 68a aan aie mounted on P. W. Board, PT0O1
20. Function Lamp ....... eee ee eee eee eee mounted on P. W. Board, PYO1
21.°: Dial LAMP 0.33 cos it ee ae ae ee we aws « mounted on P. W. Board, PZ01
2. AM TUNER
The AM TUNER portion of the 4270 is composed of one IC circuit (including RF amplifier,
local oscillator, mixer, IF amplifier, detector, and a signal strength indication amplifier) and
one transistor amplifier to amplify the detected audio signals.
All components except Tuning capacitor and ferrite bar antenna are mounted on a printed
circuit board P150.
The AM signals induced in a ferrite bar antenna are applied to the input of RF amplifier
(pin @) 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 output
and input circuit of RF amplifier assure very high image and spurious rejection performance.
Thus amplified and selected AM signals are then applied to one input of Mixer section (pin@®)
through a coupling capacitor C158. While the local oscillator voltage is injected to the other
input of the section (pin @) through a capacitor C157. Then both AM signals and oscillating
voltage are mixed 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.