Marantz 4070 - Power Supply and Troubleshooting; Power Supply Unit Functionality; Trouble Analysis Guide

Excessive
current
flow
in
the
power
stage
are
detected
by
the
resistors
H747
and
H749
and
the
resultant
variations
are
applied
to
the
transistors
H707
and
H709
and
make
them
turned
on.
This
decreases
the
base
biasing
current
for
H711
and
H713.
In
this
way
the
current
flow
in
the
power
stage
(HOO1
and
HO03)
is
restricted
within
a
safe
value.
9. POWER SUPPLY UNIT
The
power
supply
unit
consisting
of
transistors
H811
and
H812,
which
operates
as
an
automatic
voltage
regulator,
provides
+35V
DC
to
all
of
the
amplifiers
except
main
amplifiers.
10. TROUBLE ANALYSIS
1. Excessive line consumption
2. No line consumption or zero bias
3. Excessive hum and noise
4, Parasitic oscillation
5. Improper clipping
105 TO 125VAC
50/60 Hz
SLO-BLO
VARIAC
AC WATTMETER
0 TO 150 WATTS
ot
ie
WATTMETER
Check for shorted H0O7, C001, COO2.
Check for shorted transistor HOO1 through
HO04.
Check L001 for short.
Check line cord, fuse, shorted HOO5, HOO6G,
H718, H719.
Check for open rectifiers HOO7, or open
LO01.
Check
filter
capacitors
C001,
C002,
H811,
H812.
Check for defective C711, C712, C713,
C714, C721, C722, C732, C733.
Check for proper adjustment R715 and
R716.
Check for shorted transistor H711 through
H714.
AC OUTLETS
AC VOLTMETER
0 TO 150VAC
Figure
1.
AC
Power
Control
Box
Simplified
Schematic
ry