Marantz 2270 User manual

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TABLE OF CONTENTS
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Phono and Tone Amplifiers ............ 00: c cece eee ene eens nr ee :
Power Amplifier ........... Sse SU woetedbta ae Sete ead raveee dara Sie Sisiy anes ath eae oo eee hs
Power Protection Circuit.......... SUMS Baie ee Ra BAe ere et ee OM ES a aoe ad a RE Sih ies
Speaker Protection Relay Circuit .................... Se eC ee Se rae
Suggestion for Trouble Shooting of Power Amplifier ........ aes varhan'e ratte. Sieh ee ie we ate oe
Voltage Conversion... 1.2.2... 0.0. c cece ete ee eee Pe gests fe and 4 ori Saas Sew alata orate
Test Equipment Required for Servicing ................. Hide e Gee wae Sao Shain hon ine Bye
AM Alignment Procedure ........... wate Roe ates eheg SS Genet aa be Sa eaten Be nual Shenae a
FM Alignment Procedure ........ 0.0. cece eee ect eee ee eee ee teeta tree nea
Stereo Separation Alignment ....... Sad Sedan We Ciey areata Solar aia at ous gs hasta eG sitar Scatiotane Wh
Muting: Circuit: AL GnMent es isi: bcc 62 c8 eie eS ew eles e per ele 8 ia ea a oie ee wD ee we wees
Audio Adjustment ............. Seles Grae ee we ee Gee eer ean bared Kays Aaa ads Oe
Parts List............. Awe gaara hoe Raa etsaN he: Bedale Soedavarte tes ee Evahe ark evades, Grararenetey
Specifications i iciw iia eis Bau seers bea hs ea ae Geen Bee Gee OA ee
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LIST OF ILLUSTRATIONS ”
FIGURE NO PAGE (
1. Remove the Terminal Cover ......... 0. cece cece eee etter e eee ecceee §
2. Voltage Conversion Chart ........ 0. ee cee ee eee eet e eee teen cceee 7
3. Lissajou Figure on Oscilloscope ....... 0... cee eee eee tee teeta eee TM
4. Dial Stringing. ...... 2... cee eee apanar stnjaete aL grayerannperesetee susdcacaeatine niet TE
5. Front Panel Adjustment and Component Locations ........ bay dvetetridand feet ices Per (74
6. Main Chassis Component Locations (Top View) ............002ececeeeeeeees .. 12
7. Rear Panel Adjustment and Component Locations ..... sib aa 8 WictECages wiikede es Cate cas me NS
8. Main Chassis Component Locations (Bottom View) ........ bagel teed er aren .. 13
9. FM Front End Assembly P100 Component Locations..............02. 000 eee eee 14
10. FM 1F Amplifier Assembly P200 Component Locations ............... 00200000) 14
11. FM Detector Assembly P500 Component Locations . gpethotabteale, ek Siwadl (o0e Seer aatnaateleud 15
12. MPX Stereo Decoding Amplifier Assembly P300 Companeht Leearions ee ee eee ia 1D
13. Muting Control Amplifier Assembly P550 Component Locations ................ . 16
14. AM Tuner Unit Assembly P150 Component Locations .......... Maan Meee Pees 16
15. Phono Amplifier Assembly P700 Component Locations ............... 2200000 e 17 A
16. Tone Amplifier Assembly P400 Component Locations ............ 0.0.0 eee eee 17
17. Tone Control Unit Assembly P450 Component Locations ............. Bie ene Sans 18
18. Power Amplifier Assembly P750 Component Locations ............ ......+5. eae 19 ‘
-19. Regulated Power Supply and Protection Relay Circuit Assembly P800
Component Locations ..................-- aed Duaia ats. eared Hae RS ee a eee 20
20. Mono, High and Low Filter Switch Unit Assembly’ P600 Component Locations...... 21
21. Loudness, Muting and Speakers Switch Assembly P650 Component Locations....... 21
22. Schematic Diagram ................-- jostee MERE Ale tare tl A Bare MN eh eats 22

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.

2.2 Suggestions for AM Tuner trouble shooting
Check for broken AM bar antenna, next try to tune station by rotating fly-wheel tuning knob
slowly and observe the AM signal strength meter whether it deflects or not. if the signal strength
meter gives a deflection at several frequencies received, no failure may exist in the stages at least
preceding final IF transformer L154. Next connect a oscilloscope to the pin terminal J162 or
J157 and check for audio signals with the tuning meter deflected. If the signal strength meter
does not deflect, check the loca! oscillator circuit. Normal oscillating voltage at the hot end of
the oscillator tuning capacitor is about 2 or 3 volts, varying with tuning capacitor position. When
measuring oscillating voltage use a RF VTVM, no circuit tester gives correct indication. If the
local oscillator voltage is normal, check all voltage distribution in the AM circuits by using a DC
VTVM and compare the measured values with those given in the schematic diagram.
3. FM TUNER
The FM Tuner section of Model 2270 is divided into five functional blocks: FM Front End, IF
Amplifier, Detector, Muting Control and MPX Stereo Decoding Circuit.
FM signals induced by a FM antenna are led to FM antenna coil L101 through an attenuator
switch and a balun coil. These signals are then applied to the FET RF amplifier which in turn
applies its output to the next FET Mixer H102 through the triple tuned high selective circuits.
The FET Mixer convert its input signal into 10.7MHz intermediate frequency and amplifies it at
the same time. The H103 is a local oscillator and its output is injected into the source of the FET
Mixer, the injection voltage is about 700mV. The 10.7MHz front end output is led to the next IF
amplifier unit through a coaxial cable.
The IF amplifier unit consists of six stages of IF amplifier, one stage of AGC amplifier and two
stages of multipath signal amplifiers. Eight pieces of ceramic filters are also used to obtain high
selectivity three stages of symmetrical diode limiters are also employed for the best limitting
characteristics, improved capture ratio and good AM suppression.
A part of FM Front End output is applied to the AGC amplifier H207 and rectified its output
is fed back to the gate of FET RF amplifier to decrease the gain with increased signal strength.
The signals required for multipath indication are obtained from the three stages of IF
amplifiers through coupling capacitors C234, C236 and C238 respectively and rectified by three
pair of full wave diode circuits. Thus obtained AM components of the FM signal is amplified by
the transistor H208 and H209 and its output is again rectified to obtain DC current required for
actuating the Multipath indication meter.
The IF signal sufficiently amplified through every stage of IF amplifier is finally applied to the
IC limiter on the Detector Unit. The detected audio output is led to the buffer amplifier H502
and its buffered output is led to; (a) noise amplifier H551 through resistor R551 and capacitor
C551, (b) Quad Radial Jacks on the rear panel through resistor R564, (c) MPX stereo decoding
circuit through R563.
The DC current caused at the third windings of the discriminator transformer is directly
applied to the FM center tuning meter.
Audio Muting and Stereo mode auto-selecting circuit
The muting circuit consisting of all solid-state electrical switching has been incorporated in the
Model 2270. Three inputs control the muting function. The first is related to signal strength, the
second to the noise condition at the detector and the third is derived from the DC component
of the detector output. These inputs are properly matrixed and gated to provide muting free
from noise and transients.
The first input of DC voltage obtained by rectifing a part of IF output signal from the H206 is
applied to the base of H306 and turns on it, if the IF output is greater than predetermined level
(muting threshold level). When the H306 is turned on the H307 is turned off, allowing the
emitter-collector resistance increasing and the collector voltage rises about 9.7V. The increased

collector voltage increases the gate bias voltage and turns on the switching FET H308, decreasing
the source-drain resistance to near zero ohm and allowing the audio signal applied to the source
to flow to the center of 38KHz switching transformer through the source-drain path.
When the input signal is lower than predetermined level, the DC output obtained is small and
can not turn on the H306, thus the H306 keeps its turn-off state and this makes H307 turn on,
decreasing the collector voltage and turning off H308. Thus no audio signals can pass through the
FET. This is the fundamental principle of the muting operation but for more elaborate muting
operation the second and the third inputs are necessary.
The second input is used to protect the muting operation and MPX stereo beacon lamps from
misoperation due to undesirable noises. The high frequency noises included in the detected audio
signals are separated by a small capacitor C551 and amplified by the noise amplifier transistor
H551 and its output is rectified by the two diodes. The rectified DC output is proportional to the
noise components in the audio signals.
When there are excessive noises in the audio signals such as obtained with a station incorrectly
tuned in, the rectified DC output turns on the transistor H522, decreasing the emitter-collector
resistance to zero. This means the collector of H307 is short-circuited to the ground, therefore
the H308 is turned off and any audio signals having excessive high frequency noises can not go
through the FET’s sourcedrain path.
The transistor H303 connected in series with the 19KHz pilot signal amplifier transistor H302
is also turned off (when the transistor H522 or H307 are turned on.) and no current flows in the
H302, resulting in turning off the streo beacon lamps. Thus misoperation due to undesirable
noises is also avoided.
The third input is obtained from the FM discriminator circuit. The DC output so called ‘’S’’
curve is applied to the gate of H558 through a resistor R523 and deviding network (R565 &
R566). The DC output is zero with a station correctly tuned in, but will vary from negative to
positive values or vice versa when the tuning point is deviated toward either plus or minus
frequency from the correct tuning frequency.
When the DC output is increased to a greater level than that of predetermined, the increased
source potential of H558 makes the transistor H561 turn on, and this makes the H306 turn
off,....H307 turn on, .... H308 turn off, .... H303 turn off (this means no 19KHz pilot signal is
amplified and no stereo beacon is turned on.) When the DC output is increased to the negative
predetermined level, the decreased source potential turns off the H559 which in turn makes the
H560 turn on and the H306 is turned off. The subsequent changes are exactly the same as that
just described above. ;
Thus when the tuning is shifted or deviated to the certain frequencies in which undesirable
noisy side-audio signals are produced, both muting and 19KHz switching transistors are operated
automatically and open the circuits.
With the station correctly tuned in, the bias current of the FET H558 is adjusted so that both
transistor H560 and H5671 are not turned on, giving no effect on the transistor H306.
MPX Stereo Decoding Circuit
The buffered and non-equalized audio signals are applied to the first amplifier H301 which
serve as a tuned amplifier for the pilot signal in the composite signals and as a buffer amplifier for
the audio signals. The amplified 19KHz pilot signal is led to the second 19KHz amplifier H302
and further amplified if switching transistor H303 in turned on by the controlling DC signal as
described in the preceding chapter. The final 19KHz pilot signal is rectified by the doubler circuit
consisting of the H315 and H316 to obtain synchronized 38KHz amplifier driving signal.
The H304 is the 38KHz tuned amplifier and supplies its output to the switching matrix circuit
consisting of four diodes. While the composite signals are applied to the center tap of switching
transformer 1/2 L302. The right and left stereo signals decoded by the switching circuit are led to
the crosstalk cancelling amplifier which utilizes complementary configuration with NPN and PNP

transistors through de-emphasis network consisting of C315 and R335, and C316 and R336.
L305 is a low-pass filter networks having very sharp cut off characteristics and eliminates
undesirable residual switching signals. Transistors H313 and H314 are buffer amplifiers and their
outputs are led to the function switch.
3.2 Suggestion for Trouble Shooting of FM Tuner
3.2.1 Symptom: No FM Reception
First turn on the power switch and try to tune FM stations. Rotate the fly-wheel tuning knob
slowly and observe the FM signal strength meter and FM center tuning meter. If the center tuning
meter deflect at several frequencies received, the tuner circuits preceding the discriminator circuit
may have no failure. If the signal strength meter deflect but no deflection is obtained on the
center meter, there may be some defects around the detecting circuit consisting H501, L501,
H503, H504, etc. When no reading is obtained in both meters, 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 both meters deflect but no sound is obtained,
check audio circuits, using high sensitive oscilloscope.
3.2.2 Symptom: No Stereo Separation
First check the ‘‘“MONO”’ switches are 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 19KHz pilot signal and 38KHz
switching signal, using an oscilloscope.
4. Phono and Tone Amplifiers
Program source signals from the PHONO jacks on the rear panel are supplied to the input
circuit of the Phono Amplifier through the selector switch and the output of the Phono
Amplifier is applied to another section of the selector switch. This amplifier provides a gain of
40dB.
All signals selected by the function switch (SO02-3F, 4F) are led to the balance and volume
controls through the MONO(L,R) and Hi-Blend switches.
Signals properly attenuated by the volume control are applied to the tone amplifier and
subjected to the tone control networks such as bass, mid, treble contro! and high and low cut
filters. .
Thus controlled audio signals are then led to the PRE OUT jacks on the rear panel.
5. Power Amplifier
The signal from the tone amplifier is applied to the differential amplifier (base of H751)
through the coupling capacitor C751. The differential amplifier provides very high input
impedance and its collector output (H752) is applied to the base of H753 which in turn applies
its Output to the next stage; to the H756 through the network R766, C762 and R771, and to the
H757 through the network R776, C763 and R772. The outputs of H756 and H757 are applied to
the H758 and H757 respectively. HOO1 and HOO2 are power transistors used in complementary
symmetry configulation and mounted on the heat sink.
To maintain overall amplifier stability and linearity, degenerative feed back is utilized
throughout the amplifier. This feed back is also necessary to reduce distortion to within specified
limit. The RC network R775 and C756 condition the feed back signal for the audio signals. R759
and C755 are also a feed back loop provided to obtain a stable zero DC off set voltage at the
speaker output terminals. The R762 is a trimming resistor to adjust the DC offset voltage.
Dynamic bias is applied to the base of driver transistors H758 and H757. This dynamic bias
circuit is comprised of H761, H760 and R763. This provides a variable base bias for driver

transistors that automatically maintains the proper base voltage with temperature change. The
temperature sensitive biasing components of the dynamic circuit are thermally coupled through
a heatsink to the power amplifier transistors.
6. Power Protection Circuit
Protection circuit for the amplifier is provided by sensing resistor networks and two switching
transistors. When the output transistors are over-driven, the current increase through the power
Output transistor causes an increased current flow through R789 (or R788) and the potential
across
the
R789
will
be
increased.
This
increased
voltage
potential
is
applied
to
the
base
of
H755
through the resistor R783 and turns on the H755. Since the collector of H755 is directly
connected to the base of H757, this means that the base of H757 is by-passed to the ground
through emitter-collector path of H755. Thus the input signal to the H757 is restricted to the
value
which
maintains
the
operation
of
power
transistor
with
in
the
safety
area.
A
resistor
network R777 and R781 also works as a sensing network. When the center voltage (collector
voltage of power transistors) is excessively increased to a positive value by certain troubles, the
voltage applied to the base of H755 makes the H755 turn on, making bypass circuit, and protects
the
power
transistor.
For
the
other
half
cycle
of
driving
signal,
the
same
operating
principle
is
applied provided.
7. Speaker Protector Relay circuit
The
speaker
protection
circuit
consisting
of
H808,
H809,
H810,
etc
protects
the
speaker
systems
against
any
loud
“‘pop”
sound
developed.
This
circuit
is
so
designed
that
no
sound
is
heard
for
the
first
three
or
five
seconds
after
the
power
switch
is
turned
on
by
the
time
constant
circuit
consisting
of
C807
and
R816.
This
circuit
also
portects
the
speaker
systems
against
some
troubles
due
to DC
off
balance between
the speaker
system
terminals
by
instantly
operating
the
relay
and cut off
the
speaker
systems
from
the circuit.
When
DC
off
balance
voltage
(positive)
is
developed
between
speaker terminals
by
possible
defects
such
as broken
power transistor,
short:
circuits,
or
broken
potentio
meter
R762,
as
the
base of
H808
is
connected
to
the speaker
terminal,
the
transistor
H808
is
turned
on
by this offset
voltage
developed
and
this
makes the
_
transistor
H809 and H810
turns
off,
thus
cutting
off
the
relay and
disconnecting
the
speaker from
the
output
circuit.
When
negative
offset
voltage
is
developed,
this
voltage
directly turns
off
the
H809
and H810, thus
speaker
is
cut off
from
the
circuit and
protected.
The circuit also protects the speaker systems from the possible damage when the amplifier is
over-driven by very low frequencies such as 7 or lower cycles.
8. Suggestions for Trouble Shooting of Power Amplifier
8.1 Excessive line consumption
a. Check for shorted rectifiers HOO5; also check COO7 and C008.
b. Check for shorted transistors H758 and H759, HOO1 and HOO2, or check H760. Check for
open control R763, and bias diode H761. Check L004 for short.
CAUTION: BECAUSE THE DRIVER AND OUTPUT STAGES ARE DIRECT COUPLED COM.
PONENTS MAY FAIL AS A DIRECT RESULT OF AN INITIAL COMPONENT
FAILURE. IF A SHORTED TRANSISTOR OR ZENER DIODE IS FOUND, OR
CONTROL OR BIAS DIODE, BE SURE TO CHECK THE REMAINING DRIVER
AND OUTPUT COMPONENTS FOR SHORT OR OPEN CIRCUIT BEFORE RE.
ENERGIZING THE AMPLIFIER.
8.2 No Line Consumption or Zero Bias
a. Check line cord, fuse, transistors H760, HOO1, HOO2, HOO3 and H004, bias diode H761.
b. Check for open rectifier HOO5, or open L004.

8.3 No DC Balance
a. Check R762 and Zener diodes H762 and H763.
9. Voltage Conversion
This model is equipped with a universal power transformer to permit operation at 100, 120, 220
and 240 V AC 50 to 60Hz.
To convert the Model 2270 to the required voltage perform the following steps:
(1) Remove the top cover.
(2) Remove the Transformer Wire Connection Terminal Cover, loosen two Cover mounting
screws on the rear panel, see Fig. 1
(3) Change the jumper wires as illustrated in Fig. 2 for the required AC voltage and replace the
fuse as instructed.
CAUTION: DISCONNECT POWER SUPPLY CORD FROM AC OUTLET BEFORE CONVERT-
ING VOLTAGE.
REMOVE SCREW
REMOVE THIS COVER
Figure 1 Remove the Terminal Cover

For
|OO
V
Operation
For
200V
Operation
(Use
5A
Fuse
)
(Use
3A
Fuse
)
BROWN
GREEN
WHITE
REO
BLUE
YELLOW
BROWN
GREEN
WHITE
REO
BLUE
YELLOW
For
120
V
Operation
For
220V
Operation
(Use
4A
Fuse
)
(Use
3A
Fuse
)
BROWN
GREEN
WHITE
RED
SLUE
YELLOW
BROWN
GREEN
WHITE
RED
8LUE
YELLOW
For 240V Operation
(Use 3A Fuse
BROWN GREEN WHITE REO BLUE YELLOW
Figure 2 Voltage Conversion Chart

10. Test Equipment Required for Servicing
Table 1 lists the test equipment required for servicing the Model 2270 Receiver.
Manufacturer and Model No.
AM Signal Generator Signal source for AM _ align-
ment
Test Loop Used with AM Signal generator
FM Signal Generator Less than 0.3% distortion Signal source for FM _ align-
ment
Stereo Modulator Less than 0.3% distortion Stereo separation alignment
and trouble shooting
Audio Oscillator Weston Mode! CVO-100P, less
than 0,02% residual distortion
is required.
High sensitivity with DC hori-
zontal and vertical amplifiers.
With AC, DC, RF range
Sinewave and squarewave sig-
nal source.
Waveform analysis and trouble
shooting, and ASO alignment.
Voltage measurements.
Trouble Shooting
AC Wattmeter Simpson, Model 390 Monitors primary power to
Amplifier.
AC Ammeter Commercial Grade (1-10A) Monitors amplifier output ur-
der short circuit condition.
Line Voltmeter Commercial! Grade (0-150VAC)} Monitors potential of primary
power to amplifier.
Variable Autotransformer | Powerstat, Model 116B
(0-140VAC, 10 amps.)
Shorting Plug
Adjusts level of primary power
to amplifier.
Use phono plug with 600 ohm
across center pin and shell.
Shorts amplifier input to elim:
nate noise pickup.
Output Load Commercial Grade
(8 ohms, 0.5%, 100W)
Output Load
(4 ohms, 0.5%, 100W)
Provides 8-ohm load for ampli
fier output termination.
Commercial Grade Provides 4-ohm load for ampl-
fier output termination.