Marantz PM350 - Amplifier Core Functions and Troubleshooting; Introduction to the Marantz PM350 Service Manual; Pre-Amplifier Signal Path and RIAA Equalization; Main Amplifier Circuit and Low Filter

MODEL PM 350 STEREOPHONIC AMPLIFIER
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1. INTRODUCTION
This service manual was prepared for use by Authorized
Warranty Stations and contains service information for
the Marantz Model PM350 Stereo Console Amplifier.
Servicing information and voltage data included in this
manual are intended for use by knowledgeable and expe-
rienced personnel only. All instructions should be read
carefully. No attempt should be made to proceed without:
a good understanding of circuitry operation.
The parts list furnishes complete ordering information.
Most replacement parts should be ordered from the
Marantz Company. However, a simple description is
included for parts which can be obtained locally.
2. PRE-AMPLIFIER
Signals from the TUNER and AUX terminals are taken
to the SELECTOR SWITCH (SS02).
Signals from the PHONO terminals pass through the phono
amplifier (0401) where they are amplified by 35.5dB and
at the same time undergo RIAA equalization, before going
‘to the SELECTOR SWITCH (SS02).
After being selected by the SELECTOR SWITCH, the
incoming signals are taken to the TAPE MONITOR
SWITCH and TAPE OUT terminals.
Signals which enter from the TAPE IN terminals are
taken to the TAPE MONITOR SWITCH.
Signals which are selected by the TAPE MONITOR
SWITCH are taken to the BALANCE and VOLUME poten-
tiometers, and then enter the pre-amplifier (QEO1). The
pre-amplifier has a gain of 18 dB. The signals from the
pre-amplifier enter TONE AMP (QE0Q2) and the frequency
response is controlled by the BASS, MID and TREBLE
controls, ;
After passing through the pre-amplifier, the signals enter
the main amplifier.
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3. MAIN AMPLIFIER
The main amplifier contains an 6 dB/OCT type high pass
filter network which can be switched in and out of circuit
by means of the LOW FILTER switch.
4. TROUBLESHOOTING ANALYSIS
1. Excessive line consumption
a. Check for shorted Q801.
b. Check for shorted transistor Q729 through 0732.
c. Check for open O709, 0710, R725, R726.
2. No line consumption or zero bias voltage
a. Check line cord, fuse, check for shorted Q709,
Q710, R725, R726
b. Check for open rectifiers 0801 or open L001.
3. High hum and noise level
a. Check filter capacitors C801, C802, C807, C808.
b. Check transistors Q807, Q808.
5. POWER AMPLIFIER ADJUSTEMENT
ADJUSTMENT OF IDLING CURRENT
Connect
a
DC
voltmeter
to
between
emitters
Q729
and
Q731.
Adjust
R725
until
11mV
is
reached.
Likewise,
adjust
O730,
Q732
and
R726.
6. POWER LED METER ADJUSTMENT
Connect the speaker terminal output to the rated output
voltage (15.5 V, 1 kHz), and then so adjust by R X07
(LCH)
that
the
POWER
LED
METER
30W
LED
lights
up.
Adjust in the same manner by RX08 (RCH).