Jvc AXZ 911 BG Service Manual

Page 1

AXZQIIBK

SERVICE MANUAL

MODEL I40. AX'2911 BK

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Contents
Page
Safety Precautions .......................................................... 1-2 Adjustment Procedures ............................................... 1-33
Instruction Book .................. . 1-3 Schematic Diagrams . Insertion
Description of Technology 1-16 Block Diagram ........... . Insertion
Description of Major |Cs........t. 1-21 Connection Diagram . Insertion
Internal Block Diagrams of ICs 1-27 Trouble shooting ....... Insertion
Removal Procedures ..................................................... 1-32 Parts List ................................ Separate Volume Insertion
No. 20058

May1988

Page 2

AX-ZSl 1 BK

c Safety Precautions

1.

The design of this product contains special hardware and many circuits and components specially for safety
purposes. For continued protection, no changesshould 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.

. Alternations 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 manufacturer's warranty and will further
relieve the manufacturer of responsibility for personal injury or property damage resulting therefrom.

. Many electrical and mechanical parts in the product 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 replacement which does not have the same
safety characteristics as the recommended replacement part shown in the Parts List of Service Manual may
create shock, fire, or other hazards.

. 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.

Leakage current check (Electric 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, control 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 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 1,500 .0 10 W resistor paralleled by a 0.15 F AC-type
capacitor between an exposed metal part and
a known good earth ground.

Measure the AC voltage across the resistor with E (Argngj'gggERhm / u
the AC voltmeter. or marge "5:in V°
Move the resistor connection to each exposed

O 0
metal part, particularly any exposed metal part -I
having a return path to the chassis, and measure '15 M: AC FE
the AC voltage across the resistor. Now, reverse

o

Place this probe

the plug in the AC outlet and repeat each on each exposed
measurement. Any voltage measured must not 9 0 metal part
exceed 0.75 V AC (r.m.s)t This corresponds to Good earth ground

0.5 mA AC Ir.m.s).

-Warning

@PWNT

This equipment has been designed and manufactured to meet international safety standards.
It is legal responsibility of the repairer to ensure that these safety standards are maintained.
Repairs must be made in accordance with the relevant safety standards.

It is essential that safety critical components are replaced by approved parts.

If mains voltage selector is provided, check setting for local voltage.

1-2

(No. 20058)

Page 18

7 AX-291 1 BK

(3) Programmable Power Supply

(Variable Voltage Power Supply)

To improve the power efficiency of the output stage,
the power voltage should be varied according to the
input signal. But, if switching were to be done using
a thyristor, etc., the charging current of the power
supply would fluctuate due to commutation current,
and this could cause noise. For the "Digital Pure-A"
circuit, a constant current switching circuit has been
developed using newly developed low-saturation
bipolar transistors, so that the voltage drift is kept at
a fixed level. As a result, the switching operation of
the power supply can be completed in about 120
msec. With this, switching noise is greatly reduced
and effects picked up from the AC line are minimized.
(Refer to Figs 5 and 6.) Fig. 5 Voltage Switching Circuit

+
High Voltage

[-._

Ic, VCE
Control

_. Driver ._.1

Low Voltage

Voltage Switching Signal

Switching Circuit using Thyristor Voltage witching Circuit used

in "Digital Pure-A

Current

_ ._._..
Time Time

Fig. 6 Comparison between Voltage Switching Circuits

1-18 (No~ 20058)

Page 32

AX-291 1 BK

Removal Procedures

I Removing the'Top Cover

1. Remove the eight screws from the top plate to
remove the top cover.

2, Remove the eight screws from the left and right side
panels, and remove the two screws from the rear.

I Removing the Bottom Plate

1. Remove the screws holding the four feet and remove
them.

2. Remove all 30 screws holding the bottom plate to
remove the bottom plate.

I Removing the Front Panel

1. Remove the top cover. (Refer to the previous
procedure.)

2. Pull off the volume knob.

3. Remove the two plastic rivets ® holding the lamp
housing for the Digital Pure-A" indicator.

4. Take out the two lamps for the "D/A CONVERTER
DIRECT indicator and the three lamps for the "sam-
pling frequency" indicators.

5. Remove the six screws holding the front panel (three
screws on the top and bottom) and gently take off the
front panel.

I Removing the Side Brackets

When disassembling this unit, first remove the side

brackets or front panel as shown in Fig. 3, to make

subsequent disassembling of each section smooth.

1. Remove the front panel. (Refer to the previous
procedure.)

2. Remove the three screws ((8) or ((2)) holding the right
or left side bracket.

3. Remove the three screws holding the side bracket to
the bottom. (At this time,the feet should be removed.)

4. Remove the screws holding the jacks and terminals
to the rear panel.

5. Take out the wires and connectors as required.

1-32 (No, 20058)

Lamp Housing

Digital Input Board Analog lnnut Board

Side Bracket (Left) Side Bracklt (Right)

Front Panel

Fig. 3