Jvc A X900B Service Manual

Page 1

JVB

Contents

Safety Precautions ..
Service Precautions.

1. Specifications.
2. Serivicing Method For AWG # 20 Wires
With Clamping Terminals
3. Names and Functions of Controls
4. Descriptions of Technology
I Gm volume control circui
I Gm volume control used in t IS unit N
l Gm selection circuit ...........................

ubéth

Addag

5. Removal Procedures ...............
5-(1) Tone P.C. Board section
5-(2) Gm selector knob replacement..
5-(3) Power transistor section

6. Adjustment Procedures .......

7. A-X9OOB Schematic Diagram

8. Wiring Diagram

9. Block Diagram..

Parts List ........... Separate-volume Insertion

This manual combines two single volumes; Service manual and Parts list.

No. 2740
Marr 1984

Page 2

H'AaUU D

Safety Precautions

1. The design of this product contains special hardware,
_ many circuits and components specially for safety pur-
poses.

For continued protection, no changes should be made

to the original design unless authorized in writing by

the manufacturer. Replacement parts must be identical

to those used in the original circuits. Service should be
performed by qualified personnel only.

2. Alterations of the design or circuitry of the product
should not be made. Any design alterations or addi-
tions will void the manufacturer's warranty and will
further relieve the manufacturer of responsibility for
personal injury or property damage resulting therefrom.

3. Many electrical and mechanical parts in the product
have special safety-related characteristics. These char-
acteristics are often not evident from visual inspection
nor can the protection afforded by them necessarily be
obtained by using replacement components rated for
higher'voltage, wattage, etc. Replacement parts which
have these special safety characteristics areI identified
in the parts list of Service manual. Electrical compo-
nents having such features are identified by shading on
the schematics and by( A ) on the parts list in Service
manual. The use of a substitute replacement which
does not have the same safety characteristics as the re«
commended replacement part shown in the parts list in
Service manual may create shock, fire, or other hazards.

4. The leads in the products are routed and dressed with
ties, clamps, tubings, barriers and/or the like to be sep-
arated from live parts, high temperature parts, moving
parts and/or sharp edges for the prevention of electric
shock and fire hazard.

When service is required, the original lead routing and
dress should be observed, and they should be con-
firmed to be returned to normal, after reassembling.

Service Precautions

1. Before repairing, be sure to discharge the large electro-
lytic capacitors across a resistor of about 100 ohms/1
watt.

I When disassembling

1. When replacing a power transistor or IC, be sure to
apply silicone grease to the section of a new transistor
or IC which is in close contact with the heatsink, then
mount it.

2. Copper screws (red) are used for improved sound qual-
ity.

Be sure to use specified screws.

3. When removing or stretching wires on the P. C. Board,
be sure to restore them to their original routing as far as
possible.

4. When connecting a remote switch, insert it from above
as shown in Fig. 2. In this case, press it in sufficiently
in order to prevent it from floating during operaiton.

14 (No. 2740)

5. Leakage current check

(Safety for electrical shock hazard)

After reassembling the product, always perform an iso-

lation check on the exposed metal parts of the Products

(antenna terminals, knobs, metal cabinet, screw heads,

headphone jack, control shafts, etc.) to be sure the pro-

duct is safe to operate without danger of electrical
shock.

Do not use a line isolation transformer during this

check.

0 Plug the AC line cord directly into the AC outlet. Us-
ing a "Leakage Current Tester", measure the leakage
current from each exposed metal part of the cabinet,

particularly any exposed metal part having a return

path to the chassis, to a known good earth ground.
Any leakage current must 'not exceed 0.5 mA AC
(r.m.s.).

0 Alternate check method.

Plug the AC line cord directly into the AC outlet. Use
an AC voltmeter having 1,000 ohms per volt or more
sensitivity in the following manner. Connect a
1500 ohms 10W resistor paralleled by a 0.15 uF
AC-type capacitor between an exposed metal part
and a known good earth ground.

Measure the AC voltage across the resistor with the
AC voltmeter.

Move the resistor connection to each exposed metal
part, particularly any exposed metal part having a re-
turn path to the chassis, and measure the AC voltage
across the resistor. Now, reverse the plug in the AC
outlet and repeat each measurement. Any voltage
measured must not exceed 0.75V AC (r.m.s.).

This corresponds to 0.5 mA AC (r.m.s.).

AC VOLTMETEFI
E (HAVING IOOOQ/V,
OR MORE SENSITIVITY)

O C

. 0.1 5pF AC-TYPE
_.) )-

PLACE THIS PROBE
> ON EACH EXPOSED
METAL PART

'Wv
1 500!) 1 OW

GOODEARTH GROUND

Fig. 1

l:

Metal section

Fig. 2

Note: Set the switch to OFF, then mount or demount it
holding the metal section shown above.

Page 5

AASUUD

3. Names and Functions of Controls

0 POWER switch
Press In to turn the power at the unit ON. The POWER
indicator placed just above the switch will light. Press
again to turn OFF.

0 PHONES jack
Plug the headphones into the jack for private listening.
Note: Plugging in the headphones does not switch off
the speaker sound. To listen only through the
headphones, set the SPEAKERS switch to OFF.

0 REC SELECTOR
TUNER: Set to this position to listen to another
' program source while recording a broad-
- cast program.

OFF: . Set to this position when not recording or

dubbing.

SOURCE: Set to this position to record from source
connected to the PHONO, TUNER, DAD,
or AUX terminals.

S>1 >2/3: Set to this position when dubbing from
the tape deck connected to the TAPE-1
terminals to the tape deck connected to
the TAPE-2 or -3 terminals, or when re-
cording from the source selected by a
source selector button to the tape deck
connected to the TAPE-1 terminals.

2» 1: Set to this position when dubbing from
the tape deck connected to the TAPE»2
terminals to the tape deck connected to
the TAPE-1 terminals.

3> 1: Set to this position when dubbing from
the tape deck connected to the TAPE-3
terminals to the tape deck connected to
the TAPE-1 terminals.

0 TAPE SELECTOR
2. Set to this position to listen to the tape deck con-
nected to the TAPE- 2 terminals
1: Set to this position to listen to the tape deck con-
nected to the TAPE-1 terminals.
3: Set to this position to listen to the tape deck con-
nected to the TAPE-3 terminals.

0 TAPE MONITOR switch

Press in to listen to a tape deck. The indicator located

just above the switch will light. In this case, select the

required tape deck with the TAPE SELECTOR.

Notes: O When the indicator is lit, it is not possible to
listen to records or radio broadcasts. For
this purpose, press this switch again to
switch off the indicator.

0 When monitoring the recording on the
3-head tape deck (when recording while
checking the recording condition upon play-
back of recorded sounds), press in this
switch to light the indicator.

Fig.(

0 SPEAKERS switch
OFF: Set to this position to switch off the speaks
sound for listening through the headphones.
1: Set to this position to listen to the speakers cor
nected to SPEAKERS terminals 1.
2: Set to this position to listen to the speakers cor
nected to SPEAKERS terminals 2.
1 + 2:Set to this position to listen :to both speaker sys
tems simultaneously.
Note: Use the speakers with impedance of 8 ohms c
more (16 ohms if the 1 + 2 position is used) a
the rated speaker impedance of this amplifier i
8 ohms (16 ohms when the 1 + 2 position i
used). Speakers with an impedance down to
ohms (8 ohms when the 1 + 2 position is user
may be used, in Which case the temperature ris
of cabinet may not satisfy BS 415 or [EC 65.
Be sure to provide good ventilation, especial-
when speakers with an impedance of 4 ohms (
ohms when the 1 + 2 position is used) are used.

0 BASS control
Turn to the right to boost bass response and to the le
to decrease bass response.

0 TREBLE control
Turn to the right to boost treble response and to the le
to decrease treble response.

0 SUBSONIC switch
ON (L): Press in (A) to eliminate the ultra~lov
frequency noise when you fell it is annoying
OFF (1): Normally, set to this position.

® TONE switch
ON: Press in to ON when adjusting the tone with tl
BASS and TREBLE controls. The indicators loce
ed just above these controls will light.
OFF: Press again to OFF to hear the standard sow
(with flat response).

(No. 274-0) 1

Page 18

PARTS LIST

Contents

1. Main Parts Locations ......................... .. 22

2. Exploded View and Part Numbers Lis 2-3

3. Printed Circuit Board Ass'y and Parts List 2-6
3-(1) ENH-006 Equalizer P.C. Board Ass'y . 2-6

2-10
2-14
2-18
248
2-19
2-20

3-(2) ENH-OO7 Gm Volume Driver P.C. Board Ass'y
3-(3) ENH-008 Power Amplifier P.C. Board Ass'y
3-(4) TPS-255 AC Outlet P.C. Board Ass'y ........
3~(5) TPS-287 VoItage Selector P.C. Board Ass'y
4. Packing Materials and Part Numbers
5. Accessories List ................................

A-ABUU IS

(NO. 2740)

2-1

Page 35

. . mu-..

4. Packing Materials and Parts. Numbers

b
No. Part Number Part Name Q'ty Description Area
1 PK-AXSOOE Packing Case 1 E300382-341
2 NZ-AXSOO Packing Pad 1 E24600-005 (Front)
NZ-AXQOO Packing Pad 1 E24600<006 (Back)
3 E34033-012 Envelope 1 J, C, U P, E, A. G
E34033-01 2 B Envelope 1 BS
4 E35497-01 3 Caution Sheet (1 10V) 1 U, P
E35497-014 Caution Sheet (1 20V) 1 U, P
E354S7-01 5 Caution Sheet (220V) 1 E, G, P, U
E35497-016 Caution Sheet (240V) 1 A, BS, U. P
5302237-004 Sheet Assy 1
E35246-001 Serial Label 2 J, C, U, P, A, BS
E35246-004 Serial Label 2 E
E35246-006 Serial Label 2 G

The Marks for Designated Areas

J... . U. S. A.
Canada
Europe

. West Germany

2-19 (No. 2740)

U. K
Australia

. . Other Countries

. U. S. Military Market

I
5".