Marantz 4230 - Main Amplifier; BTL Connection; Power Supply Unit; Audio Trouble Analysis

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13. MAIN AMPLIFIER
Transistor
H702
is
the
pre-driver
coupled
to
the
transistor
H704
through
capacitor
C712.
The
transistor
H704
drives
the
inverter
transistors
H710
and
H712
which,
in
turn,
drive
the
power
stage
consisting
of
HOO1
and
HOO3.
Transistors
H706
and
H708
are
current
limiter
Operating
as
a
power
transistor
protection
circuit.
Excessive
current
flow
in
the
power
output
stage
is
detected
by
the
resistors
R759
and
R761
and
the
resultant
variation
is
applied
to
the
transistors
H706
and
H708
and
make
them
turned
on.
This
decreases
the
base
biasing
current
for
H710
and
H712.
In
this
way
the
current
flow
in
the
power
output
stage
(HOO1
and
HOO3)
is
restricted
within
a
safe
predetermined
value.
14. BTL (Balanced Transformerless) CONNECTION
This
power
amplifier
is
designed
to
operate
in
either
2-channel
or
4-channel
modes,
depending
on
the
setting
of
the
POWER
MODE
switch
that
incorporates
phase-conversion
and
power
switch
for
BTL
connection.
With
this
switch
placed
in
the
12Wx4
position,
this
unit
Operates
as
a
12W
4
channel
amplifier.
With
the
switch
placed
in
the
35Wx2
position,
the
unit
Operate
as
a
35W
2
channel
amplifier,
in
this
case,
the
power
output
is
obtained
only
from
FRONT
SPK
terminals.
The
transistor
H701
convert
the
phase
of
1
channel
amplifier
and
3
channel
amplifier.
15. 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
amplifiers
except
main
amplifiers
and
+14V
DC
to
the
tuner
section.
16. AUDIO TROUBLE ANALYSIS
1,
Excessive
line
consumption
a.
Check
for
shorted
rectifiers
HOO7.
b.
Check
for
shorted
transistors
HOO1
through
HO04.
Check O01 for short.
2.
No
line
consumption
or
zero
bias.
a.
Check
line
cord,
fuse,
shorted
HOOS
and
HOO6,
H718
&
H719.
b.
Check
for
open
rectifiers
HOO7,
or
open
L001.
3.
Excessive
hum
and
noise
level
a.
Check
filter
capacitors
C003,
C707,
&
C708.
b.
Check
for
shorted
transistor
H801
and
H802.
4.
Parastic
oscillation
a.
Check
for
defective
capacitors,
C710,
C71
1,
C714,
C715,
C728
&
C729.
5.
Improper
clipping
a.
Check
for
proper
adjustment
of
R727
&
R728.