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
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MEASURING
METHOD
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1.
TAPE
SPEED
DEVIATION
1.0...
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6
+
WOW
AND
FLUTTER
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3,
FREQUENCY
RESPONSE
....-
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6
4
RICNAL
TO
NOISE
RATIO
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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
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B
-
TRANSPORT MECHANISM
...-.-0-
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10
if
FORWARD
PLAYBACK
RECORDING
MODE
......
Pe
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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
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Sore
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14
1.
REEL
TABLE
HEIGHT
ADJUSTMENT
..
0.0...
0s
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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
.......
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ttn
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athchv
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fet
desc
Goad:
Saal
oS
taass
teh
16
1.
HEAD
HEIGHT
ADJUSTMENT
.......
0.0002
te
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reese
BAG
Parity
arg
ites
anette
16
2,
HEAD
AZIMUTH
ALIGNMENT
ADJUSTMENT
....
26-02
-
seer
ees
17
AMPLIFIER
ADJUSTMENTS
1.0.0.0
00
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teeter
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18°
1.
PLAYBACK
OUTPUT
LEVEL
ADJUSTMENT
......000
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ree
18
3.
VU
METER
SENSITIVITY
ADJUSTMENT
.....
St
dnokudiend
upesoe
ata
peated
18
3.
HIGH
RANGE
VARIATION
CHECK
2.0.0.0
2.
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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
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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