Akai GX-225D User manual

:
PART SUSTEY

MODEL GX-225D
MODEL GX-221
STEREO TAPE DECK
° MODEL GX-225D
. ALSO APPLICABLE TO MODEL GX-221 STEREO TAPE
. RECORDER AND GX-221D STEREO TAPE DECK
SECTION 1 SERVICEMANUAL ........-.6-¢2 20 eee 3
SECTION 2 PARTSLIST ........... ia aesesets. 4s fs 6 ase
SECTION 3. SCHEMATIC DIAGRAM ........-.--.+.---60

_ *
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SECTION 1
SERVICE MANUAL
TABLE OF CONTENTS
SPECIFICATIONS
2.000
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MEASURING
METHOD
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1.
TAPE
SPEED
DEVIATION
1.0...
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+
WOW
AND
FLUTTER
..
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6
3,
FREQUENCY
RESPONSE
....-
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6
4
RICNAL
TO
NOISE
RATIO
\-soidw
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OR
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6
5.
TOTAL
HARMONIC
DISTORTION
FACTOR
....-0..00
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7
6.
CROSS
TALK
(Cross
talk
between
the
channels)
.
06-66
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ERASE
RATIO“
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289
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7
8.
POWER
OUTPUT
.....
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VCE
ERAGE
SD
2
7
DISMANTLING
OF
UNIT
.......000
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B
-
TRANSPORT MECHANISM
...-.-0-
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10
if
FORWARD
PLAYBACK
RECORDING
MODE
......
Pe
er
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it
.
FAST
FORWARD/REWIND
MODE
......-
20sec
eee
ere
ee
teeters
11
:
BLOCK
DIAGRAM
OF
VOLTAGE
SUPPLY
CIRCUIT
TO
MOTOR
AT
EACH
MODE
....
!1
4.
SYSTEM
CONTROL
CIRCUIT
OPERATION
,..
0.2000
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13
MECHANISM
ADJUSTMENTS
........-0
0-0-0
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Sid
Sore
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14
1.
REEL
TABLE
HEIGHT
ADJUSTMENT
..
0.0...
0s
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eee
eee
eee
ets
14
2,
PINCH
WHEEL
PRESSURE
MEASURING
METHOD
Aiki
ated
rks
he
eine
bee
14
3.
BRAKE
TENSION
ADJUSTMENT
..
2.0.0
eee
ee
eter
eres
15
4,
SUPPLY
VOLTAGE
AND
TENSION
AT
VARIOUS
OPERATING
MODES
......----
15
HEAD
ADJUSTMENTS
.......
sos
se
ttn
od
athchv
a
du
Ns
fet
desc
Goad:
Saal
oS
taass
teh
16
1.
HEAD
HEIGHT
ADJUSTMENT
.......
0.0002
te
eee
reese
BAG
Parity
arg
ites
anette
16
2,
HEAD
AZIMUTH
ALIGNMENT
ADJUSTMENT
....
26-02
-
seer
ees
17
AMPLIFIER
ADJUSTMENTS
1.0.0.0
00
cece
ee
teeter
eee
eee
18°
1.
PLAYBACK
OUTPUT
LEVEL
ADJUSTMENT
......000
00
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rece
ree
18
3.
VU
METER
SENSITIVITY
ADJUSTMENT
.....
St
dnokudiend
upesoe
ata
peated
18
3.
HIGH
RANGE
VARIATION
CHECK
2.0.0.0
2.
cee
eee
et
eet
nneee
18
4.
RECORDING
LEVEL
ADJUSTMENT
..........
Bacio
Gaerne
ein
Aiae
&
Bitte
Bushs
21
5.
RECORDING
BIAS
FREQUENCY
MEASURING
METHOD
.........--
2022s
2
6.
RECORDING
BIAS
VOLTAGE
ADJUSTMENT
(Frequency
Response
Adjustment)
.-....-
21
_
AUTOMATIC
NOISE
REDUCTION
AMPLIFIER
ADJUSTMENTS
(GX-225D)
......-+++22
i
AN
RAMP:
ADTUSTMENT
6a.
as-eGice
XS
So
hae
ae
Sed
a
SES
Si
are
Ee
Be
22
‘>.
A.N.R.
OPERATION
AND
CHARACTERISTICS
...-...---00-035
Bie
phan
Readers
23
COMPOSITE
VIEWS
OF
COMPONENTS
.....
2-22-02
e
ete
rece
rts
tte
24

i. SPECIFICATIONS
An asterisk next to a figure indicates the minimum guaranteed performance.
TRACK SYSTEM
REEL CAPACITY
TAPE SPEED
WOW AND FLUTTER
FREQUENCY RESPONSE
AKAIS.R.T. Tape
Regular Tape
SIGNAL TO NOISE RATIO
' HUM AND NOISE
DISTORTION FACTOR
TONE CONTROLS Treble
Bass
CROSS TALK
ERASE RATIO
BIAS FREQUENCY
BIAS LEAK
HIGH FREQUENCY DEVIATION
Between Channels
Between FWD/REV
REC./P.B. LEVEL |
INPUTS Mic Input
Line Input
. Din Input.
_ OUTPUTS Line Output
Din Output
Speaker Output
HEAD PHONE OUTPUT
REVERSING TIME
FAST FORWARD AND REWIND TIME
MOTORS Main Motor
" Reel Motor
Erase Head
4 track 2 channel stereo/monaural system
Up to 7” reel
7-1/2 ips(19 cm/sec.) +0.7%(*+0.8%)
3-3/4 ips(9.5 cm/sec.) £0.7%(*£0.8%)
1-7/8 ips(4.75 cm/sec.) +0.7%(*4£0.8%)
Less than 0.089%{*0.12%) R.M.S, at 7-1/2 ips
_ Less than 0.12% *0,25%) R.M.S. at 3-3/4 ips
Less than 0,20%(*0.4%) R.M.S, at 1-7/8 ips
30 to 25,000 Hz +3 dB at 7-1/2 ips
30 to 20,000 Hz +3 dB at 3-3/4 ips
30 to 10,000 Hz £3 dB at 1-7/8 ips
30 to 23,060 Hz(*36 to 22,000 Hz} +3 dB at 7-1/2 ips
30 to 19,000 Hz(*38 to 18,000 Hz) +3 dB at 3-3/4 ips
30 to 9,000 Hz(*40 to 9,000 Hz) +3 dB at 1-7/8 ips
Better than 50 dB(S3 dB with N.R. process)
* Better than 48 dB at 7-1/2 ips
* Better than 47 dB at 3-3/4 ips
* Better than 45 dB at 1-7/8 ips
* Better than 44 dB at Reverse Mode
§ mV Tone Control and Main Volume: Min.
(Model GX-221 only)
Less than 1.5%{*3%) at 1,000 Hz “0” VU Recording
12 +2 dB(Max.) and —14 +2 dB(Min.) at 10 kHz
12 +2 dB(Max.) and -10 +2 dB{Min.} at 100 Hz
(Model GX-221 only)
Better than 65 dB(*58 4B) monaural
Better than 50 dB(*43 dB) stereo
Better than 70 dB
100 kHz 2 5%
Less than —20 VU
Within 2 dB, using an 8,006 Hz 3-3/4 ips recorded tape at 7-1/2 ips
Within 3 dB, using an 8,000 Hz 3-3/4 ips recorded tape at 7-1/2 ips
441.5 dB
0.2 m¥{*0.4 mV) Impedance: 10 kQ
50 mV(*60 m¥) Impedance: 150 kQ
2 mV(low) and 50 mV{*60 mV} (high)
1,228V (4+ 1dB)} Impedance: 20kQ
0.4V
30 W total music power at 89 (GX-221 only)
20 W continuous power at 82 {GX-221 only)
30 to 40 mV at 82
2 to 6 sec.
85/65 sec., using a 1,200 ft. tape at 50/60 Hz
3 speed hysteresis synchronous motor
Type: HC-16X = oh
Revolutions: 3,000/1,500/750 r.p.m.(50 Hz)
3,600/1,800/900 r.p.m.(60 Hz)
Two 6-pole eddy current outer rotor motors
Type: 24X0-MR
Revolutions: 930 r.p.m. (50 Hz)
1,120 r.p.m. (60 Hz)
Type: E4-250
Gap: 0.6 mm
Impedance; 1952 + 10% at 100 kHz.
D.C. Resistance: 3.52
ions

Recording Head
Playback Head
TRANSISTORS
Type: R4-200
Gap: 44 + 15%
Impedance: 1,8702 at 100 kHz
D.C. Resistance: 82
Type: P4-200
Gap: 1,75y 15%
Impedance: 3 4 1k at 1 kHz
D.C. Resistance: 5002
LD3141.,.2
28C372(Y} ...1
28C871(F)..,12
28C945(Q)(R)...6
28C968(3}(4) -..3
28C458LG(C)...6
STKOLS ... 2(GX-221 only)
28C971(2)(3) RED... 2
28C1211(C}(D) , .. 1
2SD223(G)(Y)..- 1
2SCTLICE)...4
DIODES
(N.R. Amp.) (N.R. Amp.)
IN34A...7 5B2...1(GX-221 only)
10D1...3 WZ-240.,.1
lop4...1
WG-599 ... 4(N.R. Amp.}
POWER SUPPLY
100 to 240 V A.C. 50/60 Hz
POWER CONSUMPTION
INSULATION RESISTANCE
90W Models GX-225D, GX-221D
135W Model GX-221
Mare than 50 M@
INSULATION DURABILITY
DIMENSIONS
WEIGHT
500V D.C. for more than 1 min. duration,
430(W) x 425(H) x 230(D) mm (17.2" x 17” x 9.2")
20.5 kg(45.1 Ibs.) Models GX-225D, GX-221D
22.5 kg(49.5 Ibs.) Model GX-221
NOTE: Specifications subject to change without notice.

ll. MEASURING METHOD
1, TAPE SPEED DEVIATION
Frequency
counter
input
GX-225D
Line output
Fig. 1
As shown in Fig. 1, connect a Frequency Counter to
the Line output. Playback a 1,000 Hz pre-recorded
test tape. Take a frequency counter reading at the
beginning, middle, and end of tape winding during
playback. The maximum value of these respective
readings will represent tape speed deviation.
2. WOW AND FLUTTER
GX-225D Wow and Flutter
Line output Meter input
Fig. 2
Method A
As shown in Fig. 2, connect the Line output to the
Input of a Wow and Flutter Meter. Playback a
3,000 Hz pre-recorded test tape and take a wow and
flutter meter reading at the beginning, middle, and
end of tape winding. The maximum yalue of these
respective readings will represent the wow and flutter.
Method B
Supply a 3,000 Hz sine wave signal from an Audio
Frequency Oscillator and make a recording on a
blank tape at the beginning, middle, and end of tape
winding. Rewind and playback the resultant signal.
Measure wow and flutter with a Wow and Flutter
Meter. (The wow and flutter value of Method B will
be close to twice that of Method A.)
3, FREQUENCY RESPONSE
GX-225D
Line
Frequency input ane
Oscillator
ae 8
output
High Sensitivity
V.T.V.M,
Fig, 3.
For
measuring
frequency
response,
connect
instru-
ments
as
shown
in
Fig.
3
and
proceed
as
follows:
1) Supply a 1,000 Hz sine wave to the Line input
from an Audio Frequency Oscillator through’ an
Attenuator.
2)
Set
recorder
to
recording
mode
and
turn
recording
level
contro!
volume
and
line
output
level
control
volume
to
maximum,
Adjust
attenuator
to
obtain
a+4
dB
V.T.V.M.
reading.
3)
Under
conditions
described
in
2)
above,
re-adjust
attenuator
so
that
the
Line
Output
is
—16
dB,
and
record
30
to
22,000Hz
at
7-1/2
ips
spot
fre-
quencies.
4)
Rewind
the
tape
and
playback
from
the
beginning.
Take
V.T.V.M.
spot
frequency
readings
and
plot
values
on
a
graph.
.
NOTE:
When
measuring
frequency
response,
new
tape
should
be
used.
4, SIGNAL TO NOISE RATIO
GX-225D High Sensitivity
Line output VIVM,
Fig. 4
As
shown
in
Fig.4,
connect
a
High
Sensitivity
V.T.VM.
to
the
Line
output.
Playback
a
250
Hz
“Q”
VU
pre-recorded
test
tape
and
mieasure
the
output.
Then
remove
the
tape
and
measure
the
noise
level
under
the
same
condition,
Convert
each
of
the
measured
values
into
decibels.

- §, TOTAL HARMONIC DISTORTION
GX-225D
Line
input —Line
output
Audio
Frequency
Oscillator
Distortion
Meter
Fig. 5
Connect the measuring instruments as shown in Fig. 5
and record a 1,000 Hz sine wave signal at “0” VU.
Playback the resultant signal and measure the overall
distortion factor. Measure the noise level of the tape
recorder without the tape. Connect the audio fre-
quency oscillator directly to the distortion meter for
measurement of the distortion factor of the oscil-
lator. The required distortion factor can be obtained
from the results of the above measurement by the
following formula:
do =d—di —d2
where, do = Required distortion factor
d = Overall distortion factor
di = Noise level
d2 = Distortion factor of the oscillator
NOTE: When measuring the distortion factor, new
’ tape should be used.
6. CROSS TALK |
(Cross talk between the channels}
(TAPE)
REV
oy Se ees
GS TAPE DIRECTION
Fig. 6
As shown in Fig. 6, first record a 1,000 Hz sine wave
signal on Track No. 3 at +3 VU level. Next, record
under a non-input condition. Then, playback the tape
on Tracks No. 3 and 4 (reversed condition of tape)
through the B.P.F, (band pass filter sensitivity ...
1:1) and obtain a ratio. between the two from the
following formula: ,
Eo
E2—-E1
where, C = Desired cross talk ratio (dB)
Bo = 1,000 Hz signal output level [i
’ Be = 1,000 Hz cross talk level
Ei =Non-input signal recorded level Bax
'C = 20 log
(dB)
7. ERASE RATIO
As shown in Fig.4, connect a High Sensitivity
V.T.V.M. to the Line ouput. Playback a virgin tape
and take a V.T.V.M. reading of the output level.
Next, record a 1,000 Hz sine wave signal at +3 VU,
‘then playback this recorded signal and take a
V.T.V.M., reading of the output level. Next, using this
pre-recorded tape, record under a non-input condi-
tion and take a reading of the noise level output of
the erased signal and obtain a ratio between the two
from the following formula:
Eo
Er = 20 log (dB)
E2-E1
where, Er = Desired erase ratio (dB)
Eo = 1,000 Hz signal output level
Ez = Non-input signal recorded level
Ex = Virgin tape noise output level
8. POWER OUTPUT (GX-221 only)
High
Sensitivity
output V.T.VM.
Fig. 8
As shown in Fig. 7, connect an 89 dummy load
resistor to the speaker output and connect this
terminal to a High Sensitivity V.T.V.M. Playback a
250Hz “0” VU pre-recorded test tape and take a
V.T.V.M. reading of the output level. The resultant
output can be obtained from the above measurement
by using the following formula:
al -2
P= Ww)
where, P = Desired power output (watts)
E = Measured voltage (R.M.S.)
R= 8&Q

Il. DISMANTLING OF UNIT
In case of trouble, etc. necessitating disassembly, please
disassemble in the order shown in photographs. Reas-
semble in reverse order. SIDE PLATE
h
REAR PLATE

MECH. BLOCK
&
MECHANISM ADJUSTMENT
LOWER FRAME
cena -
P.B. AMP. P.C. BOARD
REC. AMP. P.C. BOARD
CARD HOLDER 7
SCREWS

IV. TRANSPORT MECHANISM
Fig. 10 F.FWD/RWD MODE
10

I
1.
FORWARD
PLAYBACK
RECORDING
2.
FAST
FORWARD/REWIND
MODE
MODE
(Refer
to
Fig.
9)
(Refer
to
Fig.
10)
Setting
Recording/Playback
lever
(A)
to
playback
1)
Setting
Fast
Forward/Rewind
lever
(B)
to
Fast
position
causes
brake
lever
(E’)
to
move
in
the
Forward
or
Rewind
position
causes
brake
lever
direction
of
the
arrow
and
release
the
brake
of
both
(E')
to
move
in
the
direction
of
the
arrow,
and
torque
motors,
and
at
the
same
time,
operation
micro
release
the
brake
of
both
torque
motors,
and
at
switch
(SW-006)
is
turned
ON
by
lever
(G),
and
the
the
same
time,
operation
micro
switch
(SW-006)
is
torque
motors
begin
to
rotate
in
the
direction
of
the
-
turned
ON
by
lever
(G)
and
the
torque
motors
arrows.
Also-the
capstan
contacts
the
pinch
roller
and
begin
to
rotate
in
the
direction
of
the
arrows.
the
tape
is
transported
at
constant
speed.
2)
For
fast
forward
or
rewind,
the
mechanical
opera-
tion
is
the
same,
but
the
voltage
supply
is
different
at
each
mode.
(Refer
to
Chart
2)
3.
BLOCK
DIAGRAM
OF
VOLTAGE
SUPPLY
CIRCUIT
TO
MOTOR
AT
EACH
MODE
TAPE SPEED SW.
A.C.
100VE
7-w-3-,
—
1-%
AC, HOV ©
MAIN] MOTOR
I—o_¢ 0
Swolda —
50Hz2—~—-GOHz
P
—sHe—
NORMAL
CLOSED
CONTACT
S0Hz———60Hz
;
—t-
NORMAL
OPEN
CONTACT
Fig. 11 NORMAL PLAYBACK MODE
A.C, COM. O
50Hz—---GOHz
TAPE SPEED SW.
A.C, LOOV ©
AS. OV o
REVS swolda
S0H2——- GOHZ
ie NORMAL CLOSED CONTACT
S0Hz——~—-60Hz
—il—
NORMAL
OPEN
CONTACT
Fig.12 REVERSE PLAYBACK MODE
A.C, COM. ©
11

50Hz—=-60Hz
TAPE SPEED SW,
Ac, 100V0 7-3-3}, =e 1-%
AC TOV ©
MAIN; MOTOR
O26 ©
swoida
50Hz—-~ 6OHz
REVS
4.C. COM, O —ai— NORMAL CLOSED CONTACT
50Hz——60Hz 1 NORMAL OPEN CONTACT
Fig. 13. F.FWD MODE
‘BOH2—-GOHz
TAPE SPEEO SW.
| Y,
7-3-3, — 1-%
Swoica
' BOHz——-60Hz
REVS
A.C, COM, © —sit<— NORMAL CLOSED CONTACT
50Hz———-60Hz —k— NORMAL OPEN CONTACT
Fig.14 RWD MODE
12
oe

€020)
AT/NG
GROUNDS
| Mode
ransis- . |
tor |TRO201/ TRO202
TRO203/FRO401
TR204 |
|
| Normal | orp | oN | OFF OFF | OFF
B. 1
Ree | on | orF | on | on | oN
Chart 1
4, SYSTEM CONTROL CIRCUIT OPERATION
1) Tension Relay Operation
The tension relay functions to switch the supply
voltage only when the main motor is first started
or at reverse time when the starting torque changes
until stability is obtained. The tension relay also
prevents strong tension from being applied to the
tape when tape direction is changed by supplying
uniform voltage to both torque motors.
2) Mute Relay Operation
Because tape travel is show when the machine is
first switched to or from Forward and Reverse, the
mute relay mutes the line output signal until
proper main motor revolutions are reached.
3) System Controi Operation
In Schematic 1, at Forward Playback time,
because transistor TRO202 base bias is high when
compared with transistor TRO201, TRO202 is held
at ON condition. Consequently, the collector
_ voltage of TRO202 is low, and transistor TRO203
is OFF, Also because the condenser C0202 is
charged by the collector voltage of transistor
TRO201, the base bias of transistor TRO401 as
well as TR204 is low and is held at OFF condition.
When the Reverse Button is depressed, or the
sensing tape passes the reverse sensing pole, the
base of transistor TRO202 is grounded, the collec-
tor voltage of TRO202 increases and TRO203 is
turned ON, and because Rev. Relay RLO201
_ operates, main motor reverse revolutions begin.
REVRSE
PLUNGER SOLENOID
B.S,
9p.c, 24V
TR204 MUTE RELAY
RL206
Schematic 1
Also because of the TRO202 collector voltage
increase, the charge cument which has passed
diode
DO204
as
well
as
resistors
RO401
and
R218
and also the internal impedance of transistors
TRO401 and TR204 flows to condenser C0205,
and while this current is flowing, TRO401 and
TR204 is mdfintained at ON condition, and
Tension Relay RLO401 as well as Mute Relay
RL201 operates. :
When the main motor begins reverse revolutions
and proper tape speed is reached, the charge of
condenser C0205 will be stopped, TRO401 and
TR204 base bias will disappear and these two
transistors are turned off, the tension relay as well
as the Mute Relay is turned off, and proper reverse
mode operation begins. During reverse playback
when the FWD Button is depressed or the sensing
tape passes the FWD sensing pole, the base of
transistor TRO201 is grounded, TRO201 is turned
off and the collector voltage increases.
Accordingly, transistor TRO202 base bias becomes
high, TRO202 is turned ON and the collector
voltage decreases, At this time, TRO203 is turned
OFF, and Rev, Relay RLO201 is also turned OFF.
Thus, main motor revolutions are switched to
normal playback direction, Also because of the
TRO201 collector voltage increase, as at reverse
time, charge current flows to condenser C0202,
and transistor TRO401 and TR204 are turned ON.
Consequently, Tension Relay RLO401 as well as
Mute Relay RL201 operates. The main motor
begins forward revolutions and when proper tape
speed is reached, condenser C0202 charge will be
stopped, the Tension Relay as well as Mute Relay
is turned OFF, and proper forward mode opera-
tion begins.
At Stop or Recording mode, voltage is supplied to
TRO202 base, and because Reverse Button and
sensing tape is irrelevant, main motor revolutions
are always in forward playback direction.
i
13

V. MECHANISM ADJUSTMENTS
Nie
HHL
om
a
Els
tit
/
REEL TABLE HEIGHT
REEL TABLE
ADJUSTMENT SCREWS
~ Fig, 15
1, REEL FABLE HEIGHT ADJUSTMENT
As shown in Fig. 15, loosen reel table height adjust-
ment screws, and adjust reel table height by moving
table in direction of arrow and positioning so that ne
tape winds in the center of the reel.
2, PINCH WHEEL PRESSURE
MEASURING METHOD
Measure pinch wheel pressure with a tension gauge as
shown in Fig. 16. Read the value on the tension gauge
as soon as the pinch wheel separates from the tape _—
and tape travel stops. Ideal pinch wheel pressure is Fig. 17
1.8 kg.
14

3. BRAKE TENSION ADJUSTMENT
1) As shown in Fig. 17, use a 60 mm diameter tape
wound on a 5” reel and measure the brake tension
with a tension gauge. Ideal brake tension is from
300 to 370 grams.
2) Brake tension adjustment can be made as follows:
(Refer to Fig. 18)
a) Change position of suspended spring (a).
b) Loosen screws (b) and (c) and adjust the
vertical position of spring suspension metal (d).
c) Loosen screws (e) and (f) and adjust the
horizontal position of brake band suspension
metal (g).
d) Only the left side is shown in Fig. 18, but the
right side must be adjusted in the same way.
NOTE: In making brake tension adjustment, at all
modes except stop mode, confirm that the
brake band completely separates from the
cloth tape on the brake drum. (Refer to
Fig. 18)
Fig. 18
4. SUPPLY VOLTAGE AND TENSION AT
VARIOUS OPERATING MODES
orque Motor |
Left Side Right Side
Mode
30 V (34 V) 60 V (68 V)
| Normal P.B. 608 200 g
60 V (68 V) 30 V (34 V)
Reverse P.B. 200 g 60g
5.8V(6V) | 94.2 V (103 Vv)
roe
Sg
460.to
480
g
94.2 V (103 V) 5.8V(6V)
ROP 460 to 480 g 15¢g
Tension Relay at) 45 V(51 V) 45V (51 V)
Operating Time 100g 100g
The voltage shown in parentheses are at 60 Hz.
Chart 2
15

VI. HEAD ADJUSTMENTS
RECORDING PLAYBACK
HEAD HEAD
—s
ee aE = |
Fig. 19
1. HEAD HEIGHT ADJUSTMENT 3) Playback Head
1) Erase Head a) At Forward Playback mode, adjust playback
head height by turning screws (F) (G) and (H)
shown in Fig. 19 to left and right until the
upper edge of the tape is the same height as the
upper edge of the left channel playback head
At Playback mode, loosen screws (A) shown in
Fig. 19 and adjust head height so that the upper
edge of the tape is about 0.1 mm lower than the
upper edge of the left channel erase head core.
2)
Recording
Head
core.
At
Playback
mode
adjust
recording
head
height
by
b)
At
Reverse
Playback
mode,
adjust
playback
turning
screws
(B) (C)
and
(D)
shown
in
Fig.
19
to
head
height
by
turning
screw
(E)
shown
in
Fig. 19 to left and right until the lower edge of
the tape is the same height as the lower edge of
the right channel playback head core.
left and right until the upper edge of the tape is
the same height as the upper edge of the. left
channel recording head core.
16

rer
2. HEAD AZIMUTH ALIGNMENT
ADJUSTMENT
1) Playback Head
a) Connect a high sensitivity V.T.V.M. to the line
output terminals.
b) Set both the Tape Speed Switch and Equalizer
Switch to 7-1/2ips (19 cm/sec), depress
STEREO Track Selector, and set the Monitor
Switch to TAPE position.
c) In case of model GX-225D, set Noise Reduc-
tion Switch to OFF position.
d) Playback an 8,000 Hz 3-3/4 ips recorded Am-
pex Alignment test tape.
e) At Forward Playback mode, turn Azimuth
Alignment Screw (F) shown in Fig. 19 to
obtain maximum line output level on both
channels.
f) After the adjustment in Item e) above has been
completed, loosen screws (I) shown in Fig. 19
and move the head gap side of the playback
head to left and right. When tension is applied
to the supply reel side and the line output level
of both channels do not fluctuate, (maximum
allowable fluctuation within +0.5/—O dB) fix
screws (I) to maintain this condition.
g) At reverse playback mode, make the same
adjustment as outlined above until the line
output level of both channels do not fluctuate.
2) Recording Head
a) Connect an audio frequency oscillator to the
line input terminals, and connect a high sensiti-
vity V.T.V.M. to the line output terminals and
load a blank tape.
b) Set both the Tape Speed Switch and Equalizer
switch to 7-1/2ips (19cm/sec.), depress
STEREO Track Selector, and set the monitor
switch to TAPE position.
c) Record a 16,000 Hz audio frequency at —10 dB
recording level.
d) At recording mode, turn Azimuth Alignment
Adjustment Screw (D) shown in Fig. 19 to left
and right until the line output level of both
channels is maximum and does not fluctuate.
e) After completing adjustment in Item d) above,
adjust gap side of recording head by bending
installation angle (J) shown in Fig. 19 to left
and right until the line output level of both
channels do not fluctuate (maximum allowable
fluctuation within +0.5/—0 dB) when tension is
applied to the supply reel side.
3.To obtain best results, repeat adjustments
outlined in paragraphs 1 and 2 above 2 or
3 times.
New blank tape should be used when making
these adjustments.
17

Vil.
AMPLIFIER ADJUSTMENTS
RIGHT CH. VU METER SENSITIVITY ADJ. VR202b SKB
RIGHT CH. P.B.LEVEL ADJ. VR20ib 20KB
RIGHT CH, REC. LEVEL ADJ. VR30Ilb 20KB
LEFT CH. VU METER SENSITIVITY ADJ. VR202 5KB8
LEFT CH. PB. LEVEL ADJ. VR20I 20KB
LEFT CH. REC, LEVEL ADJ. VR30! 20KB
LEFT CH. REC. BIAS VOLTAGE ADJ. TCSOS 7OP
RIGHT CH, REC. BIAS VOLTAGE ADJ. TCS5O06 70P
® : PLAYBACK AMP, RC, BOARD MS-5022
@® ; RECORDING AMP. P.C. BOARD MS-5023
© ; OSCILLATOR P.Cc. BOARD MS-5025
GX-225D High
Line Sensitivity
V.T.V.M.
output
Fig. 21
_—
. PLAYBACK OUTPUT LEVEL ADJUSTMENT
1) Connect a high sensitivity V.T.V.M. to the line
output terminals.
2) Set both the Tape Speed Switch and Equalizer
Switch to 7-1/2 ips (19 cm/sec.), depress STEREO
Track Selector and set the Monitor Switch to
TAPE position.
3) In case of model GX-225D, set Noise Reduction
Switch to OFF position.
4) Playback a 250 Hz ‘‘0” VU pre-recorded test tape.
5) Adjust P.B. Amp. P.C. Board playback level
adjustment semi-fixed resistors VR201 20 kB
(Left Channel) and VR20lb 20kB (Right
Channel) shown in Fig. 20 to obtain a High
Sensitivity V.T.V.M. indication of 4 dB (1.228 V)
Fig. 20
2. VU METER SENSITIVITY ADJUSTMENT
After the playback output level adjustment has
been completed, adjust P.B. Amp. P.C. Board VU
meter sensitivity adjustment semi-fixed resistors
VR202 5kB (Left Channel) and VR202b 5 kB
(Right Channel) shown in Fig. 20 to obtain a VU
meter indication of “0” VU on both channels.
3. HIGH FREQUENCY DEVIATION CHECK
1) Between Channels
When an 8,000Hz 3-3/4 ips Ampex Alignment
test tape is played back, check to confirm that the
difference in high range output level between the
left and right channel is within 2 dB.
2) Between FWD and REV Playback
Playback and Alignment test tape and check to
confirm that the difference in high range level
output between FWD and Reverse playback mode
is within 3 dB.
3) If Items 1) and 2) above are not within specifica-
tions, repeat Head Azimuth Alignment adjust-
ment. '
18

PB. LEVEL ADJ. P.B. LEVEL AD.
VR201 20KB VR20ib 20KB
VU METER SENSITIVITY ADJ. VU METER SENSITIVITY ADJ.
VR202 5KB VR202b 5KB
LEFT CHANNEL RIGHT CHANNEL
Fig.22 P.B. AMP. P.C. BOARD (Face Side)
Ears [po LW
iex-22t_ | X | O | x JO |
Se CO
lx-2e50 | X [Oo [oO | x |
Fig. 23 P.B. AMP. P.C. BOARD MS-5022 (Reverse Side) ;
TR20I, 202--- 28ca7! ©
TR203 vrs 2s0945 © ®
Audio
GX-225D
|
Left
High
Frequency
Line
Line
Sensitivity
Osci
input
output
5.
V.T.V.M.
scillator
Right
Fig.
24
19

LEFT CH. REC, LEVEL ADJ. RIGHT CH. REC. LEVEL ADJ.
VR30!1 20KB VR30ilb 20KB
Fig. 25 REC. AMP. P.C. BOARD (Face Side)
TR301, 302,303,304
“2SC871 ©
TR305--- 2SC96B@EQ)
Fig. 26 . REC. AMP. P.C. BOARD MS-5023 (Reverse Side)
FROM OSCILLATOR
REC. HEAD
FREQUENCY AUDIO
FREQUENCY
ere ©O OSCILLATOR
OSCILLOSCOPE Fig. 27
‘f,
20