Marantz 4270 - Marantz 4270 Power Amplifier; Marantz 4270 Audio Trouble Analysis

the permission of Dolbyized FM broadcasting, set the switch to 25uS position. This automatically
change the time constant to 75uS while the DOLBY switch is placed in other than DOLBY
FM positions (namely normal FM broadcast position), thus, the de-emphasis time constant for
each normal and Dolbyized FM reception will be correctly set.
13. POWER AMPLIFIER
Differential amplifier consists of the transistors H701 and H703 to provide satisfactory D.C.
stability.
The transistor H705 drives the inverter transistors H711 and H713 which, in turn, drive the
power stage consisting of HOO1 and HOO2. Transistors H707. H709 and H720 are current limiter
operating as a power transistor protection circuit.
Excessive current flow in the power output stage is detected by the resistors R742 and R744
and the resultant variation is 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 output stage (HOO1 and HOOZ2) is restricted within a safe predetermined value.
14. BTL (Balanced Transformer-Less) CONNECTION
This power amplifier is designed to operate in either 2-channel or 4-channel modes, depending
on the setting of the AMPLIFIER MODE switch that incorporates phase-conversion and power
switch for BTL connection.
With this switch placed in the 25Wx4 position, this unit operates as a 25W 4channel amplifier.
With the switch placed in the 70Wx2 position, the unit operate as a 7OW 2 channel amplifier,
in which case, the power output is obtained only from FRONT SPK terminals.
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
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.
16. AUDIO TROUBLE ANALYSIS
1. Excessive line consumption a. Check for shorted rectifiers H812 through
H815.
b. Check for shorted transistors HOO1 through
HOoOo8.
c. Check L007 for short.
2. No line consumption or zero bias a. Check line cord, fuse, shorted HOO9 through
HO10.
b. Check for open rectifiers H812 through H815,
or open L007.
a. Check filter capacitors C006, C007 & C705.
b. Check for shorted transistor H801.
4, Parastic oscillation a. Check for defective capacitors, C707, C708,
C719, C720, C721 & C722.
5. Improper clipping a. Check for defective resistor, R762 & R763.
3. Excessive hum and noise level