Jvc AX R741TN 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

Page 2

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 24

AX-R741 TN
AX-R74ZBK

Power Amplifier Adjustment Procedures

90 t

I Idling Current

(1)
(2)
(3)

(5)
(6)

Set the volume control to minimum during this adjustment.

Turn R751 and R752 fully counterclockwise before the power switch on.

Always start from cald,and allow 5 minutes to warm up before adjustmentlf the heatsink is already warm from
previous use the correct adjustment can not be made.

Connect a DC voltmeter to R773 resistors leads for lefl: channel, or w R774 for right channel.

Adjust R751 for lefi. channel, or 752 for right channel, so that the DC voltmeter becomes 7mV ~ 15mV

(N0420266) 1-25