Akai GXF 91 Service Manual

Page 2

STEREO CASSETTE DECK

WELGX-F91

THIS MANUAL IS APPLICABLE TO BOTH SILVER

SECTION 1
SECTION 2
SECTION 3
SECTION 4

AND PEARL SHADOW PANEL MODELS

CIRCUIT OPERATION DESCRIPTION . . . . 3
SERVICE MANUAL .................... 23
PARTS LIST .......................... 57
SCHEMATIC DIAGRAM ................ 76

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3. DESCRIPTION OF THE TUNING MI-COM lN/OUT PORTS (MB8841-649M)

T
ln . .
No. Port Description

1 E XTAL E Xtal Xtal oscillator terminal.

2 XTAL Xtal Xtal oscillator terminal

3 RESET RESET Mi-Com Reset input terminal Reset when L

4 IRQ TEST ENABLE The STOP MODE signal is supplied from the MECH-CON. Normally
is at H" except that this is set to L 3 seconds after the power is
turned on or when the STOP mode is established.

Accepts Auto Tuning only when set to L.
Is at H during the auto tuning, which, however, will be stopped if
L input is encountered.

5 SO

6 SI .

7 SC/TO Not in use.

8 TC

9 PD Mech-ConI The mesh. control outputs I, II and III allow 6 different modes (0)

10 P, Mech-Con II through (5) as shown in the table below Without the tuning opera-
11 P2 Mech-Con III tion, the MECH-CON outputs I, II and III are all 0, establishing
the (0) mode (tuning OFF).

During TEST", any one of the modes (1) through (S)is established.
When the test is complete, the mode (5), or (REC/PAUSE), is
established, and then the mode (0), or (Tuning OFF), after the lapse
of 50 msec.
MODE T)? (1) (2) (3) (4) RECl)
unrng ,
OFF SFOP FF RWD REC/PB PAUSE
Mesh-Con I 0 1 0 1 0 l
Mech-Con II 0 0 l 1 0 0
Mech-Con III 0 0 0 0 I l
12 P3 TEST MUTE Is at H during TEST", causing the PB output to be muted. Also,
during TEST, the H output places the external memory (1C4) in
a non-selective state (CSl )
Mutes the TEST signal output with a mode other than the TEST
mode.
13 00 INDICATOR I Are indicator outputs that provide dynamic indicator display in
14 O, INDICATOR II response to strobe signals from Pins ® ~ ® (04 ~ 07 ).
15 O2 INDICATOR III The L outputs cause the indicators to come on.
16 03 L/R SWITCH Causes switching between Lch and Rch for the PB signal to the level
CONTROL level detection circuit,
17 O4 STROBEI Causes a 4 bit signal to be output through strobe oscillation with
18 0S STROBE II coordinated timing. This signal permits dynamic display of each key
19 06 STROBE 111 input and indicator output.
20 07 STROBE IV 5...
Ims
on
i
m: Flmsq l
i l l 1 DUIV CYCLE 115
[-1 a: :2 1mm
0.25m: 025m: 0.25m: 0.25"};

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100000

OHIO! (I

0C2

a i - its

REF REC PB

REC PB REC PB

4-5. Level Tuning (Refer to Fig. 1-11)

1) A 1 kHz signal is recorded and played back with
the data (011101) obtained in the coarse level
adjustment and the difference from the original
REF value (100000) is determined, which is then
added to the first recording level data The result
is then used as the second recording level data

2) The same test is further repeated twice (Le, a
total of three tests are to be conducted.)

3) If after three tests the data obtained is outside
the specified range, two additional tests need to be
conducted.

4) [f the data is still out of the specified range after
the fifth recording/playback, an error is assumed.

5) If Dolby ON" is detected, Alevel is reduced to
1/2, and Navel/2 is used as the amount oflevel
correction (a)

4-6. Equalizer Tuning

1) The proper level must be set through recording
and playback with 7 kHz (middle range), and
14 kHz (high range, with normal tape) or 15 kHz
(high range, with CrO2 or metal tape)

2nd 4 ' 3rd 1

Fig. 1.11

2) The REF value used is 100000.
3) In addition, the information in 4-5 Level Tuning
also applies here.

4-7. Mute Circuit (During Tuning)

(Refer to Fig. 1-12)

When the test key is depressed, the Mi-Com enters the
test mode with its pin ® set to H. This activates
TR11 and TR12 on the meter drive PCB, which in
turns on TR4S and TR47 (on the Pre Amp PCB) via
D17 and D18, thereby causing the gates of TR44 and
TR46 to be at negative voltage. As a result, both
TAPE and SOURCE are shut off Thus, the test signal
is muted and therefore not made available at the
LlNE OUT during the test

0n the other hand, when pin ® of Mi-Com goes to
H", TRl of the Pre Amp is activated, causing the
Rec input (Line/DIN) to go to ground. In addition,
TRZ is turned on, deactivating TR3l As a result, the
test signal from TEST OSC is supplied to the Rec
Line Amp via R91

15