Marantz PM400 - 1. Introduction; 2. Pre-Amplifier; 3. Main Amplifier; Troubleshooting Analysis

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1. INTRODUCTION
This service manual was prepared for use by Authorized
Warranty Stations and contains service information for
the Marantz PM250/PM400 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 terminalis are taken
to the SELECTOR SWITCH (SV01).
Signals from the PHONO terminals pass through the
phono amplifier (Q401, Q403) where they are amplified
by 36 dB and at the same time undergo RIAA equaliza-
tion, before going to the SELECTOR SWITCH (SVO1).
(In the case of the PM400, signals coming in from the
PHONO
1
and
PHONO
2
terminals
are
selected
by
means
fo the SELECTOR SWITCH and then taken the PHONO
amplifier).
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 MONO SWITCH BALANCE
and VOLUME potentiometers, and then enter the pre-
amplifier (QEOQ1 and QEO3). The preamplifier has a gain
of 22 dB. The signals from the preamplifier enter TONE
AMP (QFO1 and QFO3) and the frequency- response is
controlled by the BASS, MID and TREBLE controls.
After passing through the TONE preamplifier, the signals
enter the main amplifier.
TROUBLESHOOTING ANALYSIS
1. Excessive line consumption
a. Check for shorted Q806 through Q809.
b. Check for shorted transistor Q715, through Q718.
c. Check for open Q709, 0710, R717, R718.
2. No line consumption or zero bias voltage
a. Check line cord, fuse, theck for shorted 0709,
Q710, Q717, 0718.
b. Check for open rectifiers Q806 through O809
or open LO0O1.
3. High hum and noise level
a. Check filter capacitors C808, C809, C801, C803,
Q801.
4. POWER AMPLIFIER ADJUSTMENT
ADJUSTMENT OF IDLING CURRENT
Connect a DC voltmeter to between emitters Q715
and Q717. Adjust R717 until 11 mV is reached, Likewise,
adjust 0716, 0718 and R718.
5. POWER METER ADJUSTMENT
Connect the speaker terminal output to the rated output
voltage (15.5 V, 1 kHz), and then so adjust by RX07
(LCH) that the POWER METER registers 25W PM250/
35W PM400. Adjust in the same manner by RX08 (RCH).
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