Akai PS 200 C Service Manual

Page 2

PS-I 20M PS-EDOM

STEREO PRE-AMPLI FIER
and
STEREO POWER AMPLIFIERS

PS-ZOOC
PS-I2OM
MODEL PS'ZOOM

SECTION 1 SERVICE MANUAL .................... 3
SECTION 2 PARTS LIST ......... .. 57
SECTION 3 SCHEMATIC DIAGRAM

4,-1'

Page 3

III.

VI.

VII.

SECTION I

SERVICE MANUAL

TABLE OF CONTENTS

TECHNICAL DATA . .
1. MODEL PS-ZOOC. .
2 MODEL PS-IZDM . .
3. MODEL PS-ZOOM . . .....
DISMANTLING 0F UNIT .......
I, MODEL PSvZOOC ..........
2. MODEL IFS-120M (and PS-lOOM) . .
CONTROLS ..................
1. MODEL PS-IOOC .............
2 MODEL PS-IZOM (and PS-LOOM) . .
PRINCIPAL PARTS LOCATION . .
1. MODEL PS-ZOOC ...........
2. MODEL PS-IZOM , .

3. MODEL Ts-200M . 12
CIRCUIT OPERATION , 13
1. MODEL Es-200C. . . 13
1' MODEL PS-120M(md PS-ZOOM) 15
LEVEL DIAGRAM 2]

1. MODEL PS-ZOOC . . .
1 MODEL PSAIZOM (and PS-ZOOM)
AMPLIFIER ADJUSTMENT . . I
1. MODEL PS-ZOOC .
2. MODEL PS-IZOM .
3. MODEL PS-ZOOM .

. CLASSIFICATION OF VARIOUS P.C BOARDS
L PC BOARD TITLES AND IDENTIFICATION NUMBERS, I 28
2. MODEL PS-ZOOC COMPOSITION OF VARIOUS P.C BOARDS . . . . 30
3, MODEL PS-lZOM COMPOSITION OF VARIOUS P.C BOARDS . . , . 36
4. MODEL PS-ZDOM COMPOSITION OF VARIOUS P.C BOARDS ....... 43

Fur buic adjlmmcnu. meaning mathofls. and awn-ling principlfi. In!!! to GENERAL TECHNICAL
MANUAL.

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Page 11

6)

rt

Mute Circuit (Refer to Fig. [4)

When the power of the arnplifier is turned on or off,
pop and distortion noise generate to damage the
speakers or produce unpleasant sound. The mute
circuit of Fig. 14 prevents these.

When the power is ON. point A is supplied with a
diode rectified negative pulse current and charges C44
through R101. While C44 is being charged, TR34
base is supplied with the potential from w and
turns 0N. 0n the otherhand, TR35 base potential
decreases to turn OFF. At this condition since TRSS
collector current does not flow to R95. TR36 base
potential becomes higher than the emitter potential
and TR36 is turned 0N. When TR36 is turned 0N.
collector current flows through R100 and R95 and
the PROTECTION INDICATOR DI illuminates.
When C44 is finished being charged. TR34 base
becomes negative potential and TR34 turns off.
Then the base current of TRJS turns on TR35 after
charging the time constant circuit. Relay RLl is
driven by the TRJS collector current and the main
amplifier output is connected to the speaker output.
In this conditions. TR35 emitter potential becomes
higher than the base potential so that TR36 turns
OFF and the Protection Indicator Dl lights off.

When the power is OFF, point A is not supplied with
the pulse current.

The C44 charge, therefore, discharges through R99
and raises the base potential of TR34 to turn ON
'IR34. TlUS base potential then decreases to turn off
TRJS and the relay RLl also turns off. When the
TR35 collector current stops flowing, TR36 base
potential becomes higher than the emitter potential
and turns ON to light the PROTECTION INDICA«
TOR Dl. However. since the potential of +V¢c
gradually decreases. TR36 base potential decreases to

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Fig. 14

turn OFF and the PROTECTION INDICATOR 01
also turns off.

7) Center (node) Point Voltage Detection Circuit
(Refer to Fig. 14)
When there is DC potential at the power amplifier's
speaker output terminal, the DC will flow to the
speaker in the case of OCI. circuitry and damage the
speakers. For this reason. when there is a DC
potential, a circuit is necessary to detect the potential
to turn off the mute circuit relay Ru and cut off the
speaker from the power amplifier output. This circuit
is called a center (node) point voltage detection
circuit and is shown in Fig. 14.
Ordinarily the center (node) point is 0V and TR32
and 33 are OFF. C41 is a non-pole condenser and is
grounded that there is no effect from the AC signal.
But when there is a positive DC potential at the
center point, that potential positively charges C4] on
the side opposite to the ground. Consequently, TR32
is base biased and is turned 0N. TRBl base becomes
ground potential and TR31 turns 0N. When TRJl
turns ON, TR34 base potential is increased. TR34
turns ON. and TRIS base potential decreases. When
TR35 is turned OFF, relay KL] turns OFF and the
power amplifier output is disconnected from the
speakers.
Next. it there is a negative DC potential at thecenrer
point, that potential negatively charges C41 on the
opposite side to the ground and TR33 emitter
potential becomes lower man the base potential to
turn 0N TR33. Accordingly, TRJl base becomes
ground potential and relay RLl turns off as men-
tioned earlier and the power amplifier is cut off from
the speaker.

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Fig. 15 Meter Amplifier and LED Drive Circurt

VR con mi m

8) Meter Amplifier and LED Drive Circuit

(Refer to Fig. 15.16)

The signal from the speaker output enters the
input of Meter Amplifier [Cl and comes out of
terminals 2 and a as output, The peak meter used in
these models requires approximately 40 mA of
electric current. Since the output current from 101
is not enough, the output from [Cl is current
amplified by the TR4 emitter follower circuit to drive
the meter. Also because of the large current, constant
voltage circuit, fill and TRZ, supplies the current.
TR3 equalizes TR4 V3: and TR3 V5: and equalizes
V changes due to base current changes for good

Fig. [6 LBl4DS Block Diagram

linearity to the meter input.

D4 assists in obtaining good linearity of the meter
itself. When the signal voltage increases to a certain
point, D4 provides continuity to increase the meter
drive cmrent and compensates the linearity.

lC LBl4US is used for the LED drive. Fig. [6 shows
the block diagram. The signal entering terminal 3 is
amplified and is passed to each comparator. A
resistance divided constant voltage For each level is
supplied to one side of the comparators. The IC
compares each input signal with this constant voltage
and detects it to drive the LED of each level.