Marantz 1090 - 1. INTRODUCTION; 2. PRE-AMPLIFIER; 3. MAIN AMPLIFIER; 4. TROUBLESHOOTING ANALYSIS

1. INTRODUCTION
This service manual was prepared for use by Authorized
Warranty Stations and contains service information for
the Marantz Model 1090 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 shouid 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 input jacks (TUNER, AUX, TAPE 1
& TAPE 2) are applied to the selector switch.
Signals from the PHONO 71 and PHONO 2 jacks are
applied to the other section of the selector switch, then
to the phono-amplifier and equalized for proper frequen-
3. MAIN AMPLIFIER
The main amplifier consists of differential pre-amplifiers
Q701 and Q703, class ‘A’ driver Q707, Q709 and direct-
coupled drivers Q717 and Q719.
Q713 and O715 act as current limiters.
cy response. The gain of the phono-amplifier (Q401,
Q403 and Q405) is 40dB.
The outputs of the phono-amplifier are fed to the selector
switch. The selector switch selects one of signals from
PHONO 1, PHONO 2, TUNER, AUX, TAPE 1, TAPE 2
jacks and feeds it to the TAPE MONITOR switch and
TAPE OUT jacks. The selected signal is then applied to
the MODE switch, to the balance and volume controls,
and finally to the pre-amplifier consisting of QEO1,QE03,
QE05 and QE07.
The frequency response is controlled by the Bass, Middle
and Treble controls and the resultant output is passed
to the PRE OUT jacks through the High-cut filter net-
works. These networks are switched in and out of the
circuit by the filter switches.
4. TROUBLESHOOTING ANALYSIS
1. Excessive line consumption
a. Check for shorted 0801, through 0804.
b. Check for shorted transistor HOO1, through HO04.
c. Check for open HOO5, HOO6, R733, R734.
2. No line consumption or zero bias voltage
a. Check line cord, fuse, check for shorted H005,
HO06, R733, R734.
b. Check for open rectifiers Q801, Q802 or open
L001.
3. High hum and noise level
a. Check filter capacitors C809, C810, C803, C807.
4. Parasitic oscillation
a. Check C707, C708, C709, C710, C727, C728.
5. POWER AMPLIFIER ADJUSTMENT
ADJUSTMENT OF IDLING CURRENT
Connect a vacuum voltmeter to between emitters Q721
and 0723. Adjust R771 until 12 mA is reached, Likewise,
adjust Q724, Q722 and R722.