Jvc AX R742BK Service Manual

Page 1

AX-R741TN
AXvR7AZBK

JVB
SERVICE MANUAL

AX-R741TN
AX-R74ZBK

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00 0

v

. Contents

Page Page
.. 1- 2 Block Diagram .................................................. 1-26

Safety Precautions .. .
. 1- 3

Instruction Book

Description of Major ICs . . 1-18 Schematic Diagrams Insertion
Internal Block Diagram of Other le . . 1-22 Printed Circuit Boards . Insertion
internal Wiring of FL Display . 123 Connection Diagram . ......................... Insertion
Disassembly Procedures ......... . 124 Parts List ................ . Separate-volume Insertion
Power Amplifier Adjustment Procedures . .. 1-25
No. 20266

June 1991

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AX-R74l TN
AX-R74ZBK

-Safety Precautions

1.The design of this product contains special hardware and many circuits and components
specially for safety purposes. 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. Services should be performed by
qualified personnel only.

2. Alterations of the design or circuitry of the product should not be made. Any design
alterations of the product should not be made. Any design alterations or additions will
void the manufacturers warranty and will further relieve the manufacture of responsibility
for personal injury or property damage resulting therefrom.

3. Many electrical and mechanical parts in the products have special safety-related
characteristics. These characteristics 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 are identified in the Parts List of Service Manual. Electrical components
having such features are identified by shading on the schematics and by (A) on the Parts
List in the Service Manual. The use of a substitute repalcement which does not have the
same safety characteristics as the recommended replacement parts shown in the Parts List of
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
the like to be separated 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 it should be confirmed that they
have been returned to normal, after re-assembling.

5. Leakage currnet check (Electrical shock hazard testing)
After re-assembling the product, always perform an isolation check on the exposed metal
parts of the product (antenna terminals, knobs, metal cabinet, screw heads, headphone jack,
contorl shafts, etc.) to be sure the product 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. Using a "Leakage Current Tester",
measure the leakage current from each exposed metal parts 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 0.5mA 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 1,5000 10 W
resistor paralleled by a 0.15 ,uF AC-type capacitor between an exposed metal part and a
known good earth ground. Ac VOLTMETER

Measure the AC volta e across the resistor 4

with the AC voltmeter. g E Saniéi'fisiigmfl .

Move the resistor connection to each exposed o C 0'm0'esenSIt'V'tyJ

metal part, particularly any exposed metal part

having a return path to the chassis, and 0.15/1F ACTYPE

meausre the AC voltage across the resistor. -||-

Now, reverse the plug in the AC outlet and 369 5
probe on

repeat each measurement. Any voltage M 4am, exposed

measured must not exceed 0.75VAC (r.m.s.). 150°910W metal part-

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

-Warning

1. This equipment has been designed and manufactured to meet international safety standards.

2. It is the legal responsibility of the repairer to ensure that these safety standards are
maintained.

3. Repairs must be made in accordance with the relevant safety standards.
4. It is essential that safety critical components are replaced by approved parts.
5. If mains voltage selector is provided, check setting for local voltage.

1-2 (No. 20266)

Page 15

AX-R741TN
AX-R74ZBK

Tr ubleshooting

Problem

Ponlble Cause

Solutions

No sound and no illumlnatlon.

The AC plug is not connected properly.

Plug the AC plug in properly.

No sound from speakers.

The speaker cords are not connected
properly.

Check and connect properly.

The speaker switch is set to off.

Turn on the speaker switch.
(The indicator will light up.)

Sound from one speaker only.

The speaker cords are not connected
properly.

Check and connect properly.

The BALANCE control is set to one extreme.

Adjust BALANCE control properly.

Loud hum during record playing.

Turntable not connected properly.

Check the turntable manual. Ground the turnt-
able it required.

Interference from other electrical appliances.

Try moving the power cord or plugging into
a diflerent outtet.

Howling during record playing.

Turntable too close to a speaker.

Move speakers away from the turntable.

OVERALL CHARACTERISTICS
Output power
120 watts per channel into 4 ohms at 1 kHz (DIN).

80 watts per channel into 8 ohms at 1 kHz (DIN).

75 watts perchannei, min. RMS, both channels driven, into 8 ohms from
20 Hz to 20 kHz, with no more than 0.007% total harmonic distortion.

80 watts per channel, min. HMS. both channels driven. into 8 ohms at
1 kHz With no more than 0.003% total harmonic distortion. (measured
by JVC Audio Analyzer System)

Total harmonic distortion . 0.007% (20 Hz 7 20 kHz. 8 ohms) at
75 watts

:0.007%(60HZ : 7kHz = 4: 1.
8 ohms) at 75 watts

: 5 Hz - 50 kHz (IHF, 0.05%, 8 ohms
both channels driven)

:5 HZ - 80 kHz +0. -3dB (8 ohms)

Intermodulation distortioiri
Power band width

Frequency response

S.E.A. graphic equalizer
Center frequencies : 63 Hz. 160 Hz. 400 Hz, 1 kHz, 2.5 kHz.
63 kHz. 16 kHz

:+12dB :1 dB. -12dB ti dB

: +6 dB (at 100 Hz) +4 dB (at 10 kHz)

Control range
Loudness controls

(Volume control at

~30 dB position)

EGUALIZEH
PHONO overload capacity (PHONO to REC OUT)
PHONO (MM) ; 100 mV (004% THD)
PHONO (MC) : 8 mV (004% THD)
PHONO RIAA deViation
PHONO (MM) 1 :03 dB (20 Hz 7 20 kHz)
PHONO (MC) : :05 dB (20 Hz - 20 kHz)

Recording output
Output level/Impedance

TAPE 1/DAT REC . 200 mV/1.6 kotims

Damping factor : 120 (1 kHz. 3 ohms) GENERAL

Input terminals Dimensions : 435 (W) x 147 (H) x 348 (D) mm
Input sensitivity/impedance (1 kHz) (17-3/16" x 543/16" x 13-3/4")
PHONO (MM) : 2.5 mV/47 kohms Weight : VOA kg (23 lbs.)
233%3/gmfifll ' 200 Wmo ohms Design and specifications subject to change without notice.
TAPE DAT : 200 mV/47 kohrns

Signal-tonoise ratio
PHOND (MM) : 85 dB ('66 IHF)
PHONO (MC) : es dB ('66 IHF)
CD/AUX/TUNER/
TAPE l/DAT : 100 dB (66 lHF)
PHONO (MM) : 74 dB (DIN)
CDIAUXITUNER/
TAPE 1/DAT : 75 dB (DIN)

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