Marantz 2240 User manual

peak So? Gy Ae
narexe (=) 2240

Peaaeats Bart: Bak w 4
TABLE OF CONTENTS
SECTION PAGE
Introduction «- ccc ett we tee eee ee ewe ee ee ee ete ee ee eee ee ee 1
Service Notes «s+ ste e terete eet eee cere enaee REPS Cee Te ee eee eee eee 1
PM Fuher e328 tee ek eee bes @apae eee 8S PG eee Cree eee Cae GARG ae as 1
FM Tuner «cscs t etter eres Be od ca ar eidese 20 9G alas eRe Re Wace oie eee ee eee eens 3
Phono and Tone Amplifiers ee a ee er 5
Power Amplifier -- ++: e este cece terete eee eee eee ener ene eee nent e rennet 5
Power Protection Circuit ::: +c tcc tr ttt ete ee eee wwe ee ee ee 6
Speaker Protector Relay Circuit --- +++ src t ret tte ee te eet e eee teen eee teens 6
Suggestions for Trouble Shooting of Power Amplifier--------++sr ctr re rr tree rere 7
Test
Equipment
Required
for
Servicing
«+++:
ters
crete
ret
teeter
e
eee
8
AM Alignment Procedure «+--+ secrete ttt teeter tet e eee eens ees |
FM Alignment Procedure: +++: +++ e terre rt ttre teen eee e eee ene 9
Stereo Separation Alignment «s+ eset ert ttc ere eee e eee eens Se 9
Muting Circuit Alignment -- sss ccc c rete ett e eee e eects 9
Audio Adjustiient: ost ae seta ae eee kami othe oes ek eere ae aaa oN saws 10
Parts List > sveree eid See Selec Seiad aca Mirena aed wa ew oie Sata an ake wo es 26
Specifications «6660/56 os 4s hee eee Ue aoe eee teh eile we eV raw vee ee dee ewe 37
Service Information for European Model... 1... eee eee eee eee eens 38
TABLE
1. Test Equipment Required for Servicing ........ 2... cece eee eee eee eens 8

LIST OF ILLUSTRATIONS
FIGURE PAGE
1. Block Diagram of the HA1156 -+ +++ - cece cece eee cece eee eee t teen enn ees 2
2. Remove the Terminal Cover --- +: este eect tect teen eee e teen e ra nnene nes 6
3.
Dial
Stringing
«<-+
++
eect
teeta
eae
ee
ee
ree
ere
ae
11
4. Front Panel Adjustment and Component Locations «++ -+++++ttrrrrtttr ttre tees 12
5. Main Chassis Component Locations (Top View) «--+ str trt cst s ttt tsetse 12
6. Rear Panel Adjustment and Component Locations «+++ :ssstst srt rst te eres 13
7. Main Chassis Component Locations (Bottom View) -c+ctttt ttt ttrtttrrtttees 13
8. FM Front End Assembly P100 Component Locations «+++ ++++ssttr rrr testes 14
9. AM Tuner Unit Assembly P150 Component Locations <«-+:--:+++sessteet tere ees 14
10. FMIF Amplifier Assembly P200 Component Locations -+-+-+-++trttrrttttt tees 15
11. MPX Stereo Decoding Amplifier Assembly P300 Components Locations -«+:+++e++e: 15
12. Phono Amplifier Assembly P400 Component Locations -++++++seeee terre eee eens 16
13. Power Amplifier Assembly P700 Component Locations ............0cece eee e cues 16
14. Power Supply Assembly P800 Component Locations ...........0cceceeeeeeeuees 17
15. Dolby Level Assembly PCO1 Component Locations ..........0ecceceeeeeeueees 17
16. Dial Lamp Assembly PZ01 Component Locations ..........-.eeeeeeeeeeeeeeees 18
17. Functions Lamp Assembly PYO1 Component Locations ...........0.0ee erences 18
18. Pre-Tone Amplifier Assembly PEO1 Component Locations .............0e00ee eee 18
19. High and Low Filter and Muting Switch Unit Assembly PHO1 Component Locations... 19
20. Monitor Dolby Assembly PTO1 Component Locations .......... 0. ec eee eee eee 19
21. ANT. Muting Assembly PUO1 Component Locations ..............22200eeeeeeee 20
22. Exploded Mechanical Diagram... ee eee ee eee ete t teeter neee 22
23. Schematic Diagram ++ +++ +s eee eee eee tte een ene cence ee ee eens 24
24, Rear Panel Adjustments and Component Locations for European Model .... a eieaindaa te 39
25. Main Chassis Component Locations (Bottom View) for European Model............ 39
26: ‘Voltage Conversion Chart® 4c fc sixes ceed eta ses busted ba ed eee Vea eee es 40
27. Schematic Diagram for European Model ........-- +. eee eee eee e eee enes aa latecoune 42

Pearce ars Bak 4
INTRODUCTION
This service manual was prepared for use by Authorized Warranty Stations and contains
service information for Marantz Model 2240 Stereo-phonic 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 2240 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: (FMiFront Ends 0 ecb ee oa peed ie kaeee en ce teas Mounted on P.W. Board, P100
2iy ANIME THUR ceviseicte at iceltitear boca: Sats eater pice deviated echus ameteseueye Mounted on P.W. Board, P150
Si CRM =P a xvetie S osadwdinns oa0 0 witha Jented asad ie wie Mounted on P.W. Board, P200
Gis MP Xistediccsies astound ohh a hi BoraslaraPera de oid wana o3te. pdcetet Mounted on P.W. Board, P300
5. ANT-ATT. MutingUR......... 0.0.0 cece ee eee Mounted on P.W. Board, PU0Q1
6:. Dolby: Level vs. ciciices una 4 Hike oe See Bvrbine wield Wea WA Mounted on P.W. Board, PCO1
72 “PRONO:AMDP 42%. os aie Boel e eas, olen wae Sie ea ee as Mounted on P.W. Board, P400
83. {Dial Lamp iacteiice deectae hale @ hob we ek Sols erie eee es Mounted on P.W. Board, PZ01
9. Monitor, SW... . cc eee eee eee een Mounted on P.W. Board, PTO1
10. Function Lamp ........0.. 0. cee cece eee ee eee Mounted on P.W. Board, PY01
The. (Pre-TOme: Amps ie c2d os elaare. 8 «i dhe Sn ane ace eter ee SE Mounted on P.W. Board, PEO1
AZ “Filter SBeSW cs 5.55, ane, oie eis eek eae Cece Me, Bia avelalalonet wes Mounted on P.W. Board, PHO1
13: Power AMD e:aecad ee cee bb ae ew eee en eed eee e's Mounted on P.W. Board, P700
14. Power Supply «2.0... cee eee eee cece eee eee eens Mounted on P.W. Board, P800
2. AM TUNER
The AM TUNER postion of the 2240 is composed of one IC circuit (including RF
amplifier, local oscillator, mixer, IF amplifier, and detector) and three transistors. One of them
is a signal strength indication amplifier, while the other two are amplifiers for 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
12)
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
1}. While the local oscillator voltage is injected to the other input of the section (pin 16]
through a capacitor C157. Then both AM signals and oscillating voltage are mixed and
converted into 455 KHz intermediate frequency. The resulting IF signal is applied to the IF
transformer L153 consisting of one ceramic filter and two tuned circuits.
The
output
of
L153
is.led
to
the
IF
amplifier’s
input
(pin
9)
through
a
coupling
capacitor
C162
and
amplified
to
the
sufficient
level
to
drive
the
detector.
The
detected
audio
signa
derived
from
pin 7
is
filtered
and
amplified
and
final
audio
output
is
obtained
from
the
collector
of
H153
and
applied
to
the
TAPE
OUTPUT
jacks
through
the
function
switch.

The
DC
component
of
the
detected
IF
signal
is
used
as
a
AGC
voltage
to
control
emitter
current
of
RF
amplifier
through
the
AGC
amplifier
incorporated
in
the
IC.
A
part
of
the
DC
component
is
also
applied
to
the
signal
strength
indication
amplifier
H154.
The
output
appears
at
the
collector
of
H154
and
is
level
adjusted
by
R178,
indicated
on
the
signal
strength
meter
MO04.
2.1 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
serveral
frequencies
received,
no
failure may
exist
in
the
stages
at
least
preceding
the
detector
circuit.
Next
connect
a
oscilloscope
to
the
test
point
B
or
J161
and
check
for
audio
signals
with
the
tuning
meter
deflected.
If
the
signal
strength
meter
does
not
deflect,
check
the
local
oscillator
circuit.
Normal
oscillating
voltage
at
the
hot
end
of
the
oscillator
tuning capacitor
is
about
1.5
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.
STEREO
LPF-1
76KHz
38KHz
COMPOSITE,
SIGNAL
PHASE
INPUT
DETECTOR
(PD-1)
:
AUDIO 19KHz
AMPLIFIER
STEREO
INDICATOR
LAMP
STEREO
SWITCH
PHASE
DETECTOR
(PD-2)
STEREO
|
19KHz
COMPOSITE
SIGNAL
38KHz SQUARE WAVE
AUDIO OUTPUT
Figure 1. Block Diagram of the HA1156

REBRaR Pa BEBE Z.
3. FM TUNER
The FM Tuner section of Model 2240 is divided into four functional blocks: FM Front End,
IF Amplifier and Detector, Muting Control, and MPX Stereo Decoding Circuit. FM signals
induced by a FM antenna are led to FM antenna coil L101 through 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 double tuned high selective circuits. The FET Mixer convert its input
signal into 10.7 MHz intermediate frequency and amplifies it at the same time. The H103 isa
loca! oscillator and its output is injected into the source of the FET Mixer, the injection voltage
_ is about 700 mV. The 10.7 MHz front end output is led to the next IF amplifier unit through a
coaxial cable.
The IF amplifier unit consists of five stages of IF amplifier and one stage of AGC amplifier.
Three pieces of dua! elements ceramic filters are also used to obtain high selectivity, four stages
of symmetrical diode limiters are also employed for the best limiting characteristics, improved
capture ratio and good AM suppression.
A part of FM Front End output is applied to the AGC amplifier H201 and its rectified
output is fed back to the gate of FET RF amplifier to decrease.the gain with increased signal
strength.
The IF signal sufficiently amplified through every stage of IF amplifier is finally applied to
the detector amplifier. The detected audio output is led to the buffer amplifier H208 and its
buffered output is led to; (a) noise amplifier H310 through resistor R378 and capacitor C333,
(b) QUADRADIAL jack on the rear panel through resistor R379, (c) MPX stereo decoding IC
(H321) through R301 and H301.
3.1 Audio Muting and Stereo Mode Auto-Selecting Circuit
The muting circuit consisting of all solid-state electrical switching has been incorporated in
the Model 2240. Three inputs contro! 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 rectifying a part of IF output signal from the
H205 and H206 is applied to the base of H308 and turns on it, if the 1F output is greater than
predetermined level (muting threshold level). When the H308 is turned on the H309 is turned
off, allowing the emitter-collector resistance increasing and the collector voltage rises about 9V.
The increased collector voltage increases the gate bias voltage and turns on the switching FET
H301, decreasing the source-drain resistance to near zero ohm and allowing the audio signa
applied to the source to flow to the pin 2 of decoding IC 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 H308 thus the H308 keeps its turn-off stage and this makes H309 turn
on, decreasing the collector voltage and turning off H301. Thus no audio signals can pas
through the FET. This is the fundamental principle of the muting operation but for mor
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 lamp
from misoperation due to undesirable noises. The high frequency noises included in th
detected audio signals are separated by a small capacitor C333 and amplified by the nois
amplifier transistor H310 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 H311, decreasing th |
emitter-collector resistance to zero. This means the collector of H309 is short-circuited to th: |
ground, therefore the H301 is turned off and any audio signals having excessive high frequency
noises can not go through the FET’s source-drain path.

The
transistor
H317,
also,
turns
off
when
transistor
H309
or
H311
turns
on,
and
turns
on
the
transistor
H303
connected
to
pin
8
of
the
MPX
stereo
decoding
IC.
Pin
8
is
therefore
grounded
equivalently
to
set
the
IC
in
the
monaural
mode
of
operation.
This
prevent
misoperation
due
to
undesirable
noises
when
the
FM
tuner
is
out
of
tuning.
The
third
input
is
obtained
from
the
FM
discriminator
circuit.
The
DC
output
so
called
“s"
curve
is
applied
to
the
gate
of
H312
through
a
resistor
R273
and
dividing
network
(R361
&
R362).
The
DC
output
is
zero
with
a
station
correctly
tuned
in,
but
wil!
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
H312
makes
the
transistor
H315
turn
on
(this
means
the
collector
of
H309
is
short-circuited
to
the
ground)
...
H301
turn
off,
...
H317
turn
off
...
H303
turn
on
(This
grounds
pin
8
of
the
MPX
stereo
decoding
IC,
therefore
the
decoder
is
set
in
the
monaural
mode
of
operation
and
the
stereo
indicator
lamp
turns
off).
When
the
DC
output
is
increased
to
the
negative
predetermined
level,
the
decreased
source
potential
turns
off
the
H313
which
in
turn
makes
the
H314
turn
on
(this
means
the
collector
of
H309
is
short-circuited
to
the
ground).
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
MONAU
RAL/STEREO
switching
transistors
H303
are
operated
automatically
and
open
the
circuits.
With
the
station
correctly
tuned
in,
the
bias
current
of
the
FET
H312
is
adjusted
so
that
both
transistor
H314
and
H315
are
not
turned
on,
giving
no
effect
on
the
transistor
H308.
3.2 MPX Stereo Decoding Circuit
The
stereo
composite
signal
from
the
buffer
amplifier
undergoes
a
phase
compensation
by
R301
and
C301,
is
applied
through
the
muting
switching
FET
H301
to
the
input
terminal,
pin
2,
of
the
MPX
stereo
decoding
1C
H321
on
a
PLL
(Phase
Locked
Loop)
basis,
and
decoded
into
the
left
and
right
stereo
signals,
which
become
available
at
pins
4
and
5
respectively.
These
decoded
left
and
right
stereo
audio
signals
are
introduced
through
a
low
pass
filter
composed
of
L301
to
L304
and
C311
to
C320
for
elimination.
of
undesirable
residual
switching
signal
and
through
a
de-emphasis
network
consisting
of
R325,
R326,
C321
and
C322,
into
the
npn-pnp
direct
coupled
audio
amplifier,
where
the
signals
are
amplified
to
a
required
level
for
the
output
from
J311
and
J313.
From
these
jacks,
the
audio
signals
are
led
to
the
TAPE
OUTPUT
jacks
through
the
function
switch.
Figure
1
presents
an
internal
block
diagram
showing
the
functions
of
the
PLL
basis
MPX
stereo
decoding
IC
HA1156.
The
input
stereo
composite
signal,
amplified
by
the
audio
amplifier,
is
delivered
to
the
phase
detectors
PD-1
and
PD-2.
A
part
of
the
stereo
composite
signal
is
also
applied
to
the
stereo
decoder
section.
The
VCO
(Voltage
Control
Oscillator)
produces
a
free
run
oscillation
in
the
neighborhood
of
76
KHz
with
the
time
constant
determined
by
a
capacitor
C305
and
resistors
R311
and
R312
set
on
the
outside
of
pin
14.
The
VCO
output
has
its
frequency
divided
into
10
KHz
through
the
two
stages
of
the
frequency
divider
(DIV-1
&
DIV-2),
and
is
reverted
to
the
phase
detector
PD-1,
which
contains
two
input
terminals
designed
to
produce
an
output
in
proportion
to
the
product
of
the
two
input
signals.
The
signal
applied
to
one
of
the
inputs
of
PD-1
is
the
19
KHz
square
wave
formed
through
frequency
division
of
the
76
KHz
VCO
output
signal
by
the
two
stages
of
the
frequency
divider
DIV-1
and
DIV-2,
and
the
19
KHz
pilot
signal
included
in
the
stereo
composite
signal
as
a
reference
signal
is
applied
to
the
other
input.
Therefore,
the
output
of
PD-1
which
has
passed
through
the
low
pass
filter
LPF-1
provides
DC
output
voltage
in
proportion
to
the
phase
variance
between
the
two
inputs.
This
DC
output
voltage
is
amplified
by
the
DC
amplifier,
and
supplied
to
the
76
KHz
VCO
asa
control
voltage.
This
means
that
the
output
frequency
and
phase
of
the
VCO
have
been
phase-locked
to
the
input
pilot
signal.
The
38
KHz
sub-carrier
reproduced
by
PLL
as
stated
above
is
delivered
through
the
stereo
switch
to
the
stereo
decoder
seciton
as
a
switching
signal,
thus
driving
the
decoder
section.
One
of
the

inputs of PD-2 is given the 19 KHz resulting from the frequency division completed by DIV-1
and DIV-3, whereas the other input gets the 19 KHz output contained in the composite signal,
and the output is provided with a DC output in proportion to the amplitude of the pilot signal.
This DC output is furnished through LPF-2 to the trigger amplifier which drives the stereo
indicator lamp and stereo switch. Therefore, insufficient supply of the pilot signal results in
failure to light the stereo indicator and to turn on the stereo switch located in the path of the
38 KHz switching signal, thereby avoiding a wrong stereo operation. H303 attached on the
outside of pin 8 is a switching transistor for automatic monaural-stereo switchover. When the
intensity of an incoming signal from an FM station is weaker than a predetermined level, this
H303 is turned on and pin 8 is grounded, thereby developing a condition for monaural
reception. For a forced monaural operation, switch the MODE switch to “MONO”, and H303
comes into an ‘‘On’’ condition with the positive bias voltage applied to the base, and pin 8 is -
grounded,
thereby
establishing
monaural
operation.
The
transistor
H302
connected,
externally
to
pin
14
is
intended
to
stop
the
76
KHz
oscillation
of
the
VCO
which
interferes
an
AM
signal
during
the
reception
of
an
AM
station.
When
the
function
switch
is
set
to
“AM”
position,
a
positive
bias
is
charged
on
the
base
of
H302,
H302
is
turned
on,
and
pin
14
is
grounded.
Thus,
the oscillation of the VCO is stopped, ending the interference with AM reception.
3.3 Suggestion for Trouble Shooting of FM Tuner
3.3.1 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.
If
the
signal
strength
meter
deflect
at
several
frequencies
received,
the
tuner
circuits
preceding
the
discriminator
circuit
may
have
no
failure.
When
no
reading
is
obtained
in
the
meter,
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
signal
strength
meter
deflects
but
no
sound
is
obtained,
check
audio
circuits,
using
high
sensitive
oscilloscope.
3.3.2 Symptom: No Stereo Separation :
First
check
the
‘“‘MONO”
switch
is
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
19
KHz
VCO
output
signal (J310), using an
oscilloscope
and
a
frequency
counter.
4. PHONO AND TONE AMPLIFIERS
Signals from the PHONO jacks are applied to the phono amplifier mounted on P400. The
amplified and RIAA equalized phono signals and signals from the tuner section, AUX and TAPE
MONITOR IN jacks are applied to the SELECTOR switch.
All signals selected by the SELECTOR switch (S001) are let to the balance and volume
controls through the MONO switch.
Singnals properly attenuated by the volume control are applied to the tone amplifier and
subjected to the tone control networks such as bass, mid, treble control 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
Differential
amplifier
consists
of
the
transistors
H702
and
H703
to
provide
satisfactory
D.C.
stability.
The
transistor
H707
drives
the
inverter
transistors
H714
and
H715
which,
in
turn,
drive
the
power
stage
consisting
of
HOO1
and
HO02.
Transistors
H710
and
H711
are
current
limiter

operating
as
a
power
transistor
protection
circuit.
Excessive
current
flow
in
the
power
output
stage
is
detected
by
the
resistors
R725
and
R726
and
the
resultant
variation
is
applied
to
the
transistors
H710
and
H711
and
make
them
turned
on.
This
decreases
the
base
biasing
current
for
H714
and
H715.
In
this
way
the
current
flow
in
the
power
output
stage
(HOO1
and
HO02)
is
restricted
within
a
safe
predetermined
value.
6.
POWER
SUPPLY
UNIT
The
power
supply
unit
consisting
of
transistors
H801,
H802
and
H803,
which
operates
as
an
automatic
voltage
regulator
provides
+35V
DC
to
all
of
the
audio
amplifiers
except
power
amplifiers,
and
H804
which
operates
as
the
voltage
regulator
provides
+14V
DC
to
the
tuner
section,
and
H805,
H806
and
H807
which
operates
as
the
speaker
protector
to
relay
circuit.
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
C809
and
R813.
This
circuit
also
protects
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
R707,
as
the
base
of
H805
is
connected
to
the
speaker
terminal,
the
transistor
H805
is
turned
on
by
this
offset
voltage
developed
and
this
makes
the
transistor
H806
and
H807
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
H806
and
H807,
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.
:
REMOVE SCREW
REMOVE THIS COVER
Figure
2.
Remove
the
Terminal
Cover

Dea ats Bars Bae 4
8.
SUGGESTIONS
FOR
TROUBLE
SHOOTING
OF
POWER
AMPLIFIER
8.1 Excessive Line Consumption
a. Check for shorted rectifiers HOO7, also check C004 and C005.
b.
Check
for
shorted
transistors
H714
and
H715,
HOO1
and
HOO2,
or
check
HOO5
and
HOO6.
Check
for
open
control
R719.
Check
L004
for
short.
CAUTION:
BECAUSE
THE
DRIVER
AND
OUTPUT
STAGES
ARE
DIRECT
COUPLED
COMPONENTS
MAY
FAIL
AS
A
DIRECT
RESULT
OF
AN
INITIAL
COM-
PONENT
FAILURE.
IF
A
SHORTED
TRANSISTOR
OR
ZENER
DIODE
tS
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
HOO1,
HOO2.
HOO3
and
H004,
bias
diode
HOOS
and
HOO6.
b. Check for open rectifier HOO7, or open L004.
8.3 No DC Balance
a. Check R707 and Zener diodes H701 and H704.