Sansui BA 90 Service Manual

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OPERATING INSTRUCTIONS
& SERVICE MANUAL

SOLID-STATE BASIC AMPLIFIER

SAHSIJI BA-9fl

.
5mm
SANSUI ELECTRIC COMPANY LIMITED

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Welcome to the group of proud owners of the SANSUI
BA-90, a solid state stereophonic basic amplifier from
the manufacturer of some of the worlds finest audio
components. Both in appearance and performance, the
BA-90 is professional throughout. Not a single detail
has been overlooked in designing and manufacturing
the BA-90 for optimum performance. It has been
subjected to not only numerous electrical and mechan-
ical measurements, but repeated listening tests as well.
The end result is an advanced basic amplifier with a
music power output of 90 watts, ideal for use in an
electronic crossover system for the truest high fidelity
sound reproduction ever.

It is now up to you to read the instructions contained
in this booklet to fully enjoy all the advanced perform-
ance capabilities built into the BA-90.

CONTENTS

OPERATING INSTRUCTIONS

SWITCHES AND CONTROLS .................. 3, 4
CONNECTIONS .................................. 5, 6
ELECTRONIC CROSSOVER SYSTEM ........ 7,8
HINTS ON USE .............................. 9, 10, 11
SPECIFICATIONS/CHARACTERISTICS ........ 12
SERVICE MANUAL

SCHEMATIC DIAGRAM ...................... 13, 14
TROUBLESHOOTING CHART ............ 15, 16
ALIGNMENT .................................. 17, 18
PRINTED CIRCUIT SHEETS AND

PARTS LIST ................ 19, 20, 21, 22, 23, 24

OTHER PARTS AND THEIR
POSITION ON CHASSIS .................. 25, 26

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their grounding wires to the GN D terminal.
This will usually reduce hum to a great extent.
CAUTION: Be sure that the power cord is
removed from the wall AC outlet when making
grounding connections.

comm PLATE
Bumtn unmimzoumi.

Heat Radiation

Transistors being relatively sensitive to heat,
the BA-QO is designed so that any heat radiated
will effectively escape through its bonnet.
Therefore, placing something on top of the
amplifier, encasing it in a tight cabinet or
operating it in direct sunlight may lead to a
breakdown. If any of these situations cannot
be avoided, take special care to increase the
amplifiers heat dissipation capability.

Should the Protector Operate...
While your BA-90s expensive silicon power
transistors are sufficiently protected in circuit
design, a protector circuit is also incorporated
to protect them under all operating conditions.
This circuit utilizes an SCR (silicon controlled
rectifier). Should the output circuit be short-
circuited for some reason or should excessively
large inputs flow in from the input circuit and
an overcurrent flood the power transistors, this
circuit is activated to protect the all-important
power transistors. N 0 sound will then be heard
from both or one of the speakers. There is
also the possibility that the protector operates
because of a momentary overcurrent.

Should the protector circuit operate, turn off
power immediately. Wait about 5 seconds and
turn on power again. If the amplifier should
still fail to operate normally, it is more likely
that the circuit has been activated because of
a short-circuit in the output circuit. So check
the speaker cords, speaker terminals and other
parts of the output circuit for a short-circuit.

Should the Speaker Polarities

Differ. . .

Should the right and left speakers be connect-
ed out of phase with each other (i.e., should
they differ in polarity connections), reproduced
sound will be weak in the center, with bass
response particularly weakened. This condi-
tion will be very conspicuous when you play a
monophonic record on a stereo phonograph,
listen to an FM MONO broadcast or any music
program on any broadcast band. To correct
the wrong polarity connections, simply set
either PHASE switch in its REVERSE posi-
tion. Once the polarities are thus matched, the
two speakers will sound as if there were only
one speaker in the center producing sound.

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