Jvc QLG 90 B Service Manual

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QL-GQOB

JVB linjlllgljjyiumummmumunm
_ V SERV CE MANUAL.

MODEL Q L-G 90 B

Contents

Safety Precautions .. 1 10. Block Diagram ...........................

1 . Features 2 11 . Check of Power Supply P.C. Board

2. Specifications .. 2 12. Adjustment Procedures ...........

3. Controls and Functions . . 1- 3 12-(1) Lead-In Adjustment

4. Servicing Precautions . 1~ 5 12-(2) Offset Adjustment

5. Technical Explanation . 1- 5 1243) Track interval Detection Sensor Sensitivity
5-(1) Programmed Music Scan . . 5 Adjustment ...................................... 1 -1 2
5-(2) Explanation of Microprocessor 1 2-l4l Detect Position (Touch-Down Position)

Pins (M388401MI292K) Adjustment
6. Stylus Replacement ........... . 1 - 13. Connection Diagram .

14. Troubleshooting

6

8

6-(1) Removal ..... 8
8 14-(1) WhenTonearm Actloms norma
8
9
9

6-(2) Attechmen1....
7. Cartridge Replacement .

1 4-(2) When Turntable Operation is Abnormal .. 1 -1 7
14-13) When Nusic Scan Operation is

8. Disessembly .....................
8~(1l Disassembly Procedure. Abnormal ......... 1-21
8421 Removal and Attachment of Platter 15. Standard Circuit Diagram .. 1-22
compartment Door ............. 1-10 16. Power Cord Connections in Different Areas ....... 1 -24
9. Rope Suspension ............... Pans List ............. Separate-volume lmenion
This manual combines two single volumes; Service manual and Parts list. 0. 27 1 7

Mar. 19 84

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QL-GQOB I

Safety Precautions

1. The design of this product contains special hardware,

many circuits and componets 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 per-
formed by qualified personnel only.

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

3. Many electrical and mechanical parts in the product
have Special safetyrelated characteristics. These
characteristics are often not evident from visual inspec-
tion 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 l A ) on the parts list in Service
manual. The use of a substitute replacement which does
not have the same safety characteristics as the recom-
mended replacement part shown in the parts list in Ser-
vice 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
separated from live parts, high temperature parts, mov-
ing parts and/or sharp edges for the prevention of elec-
tric shock and fire hazard.

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

5. Leakage current check

(Safety for electrical shock hazard)
After reassembling the product, always perform an
isolation check on the exposed metal parts of the
Products (antenna terminals. knobs, metal cabinet,
screw heads, headphoneiack, 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 lr.m.s.l.

O 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 Si 10 W resistor paralleled by a 0.15 HF 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
return 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 0.75 V AC
lr.m.s.l. This corresponds to 0.5 mA AC (r.m.s.l.

AC VOLTMETER
lHAVlNG 1000 WV,
OR MORE SENSlTlVlTYl

r0 l
0,15 uF AC-TYPE

r-ih-

W-4
150012 10w

PLACE THIS PROBE
ON EACH EXPOSED

GOOD EARTH GROUND METAL PART

CAUTION Before selecting the Voltage selector swtich" to proper voltage disconnect the power plug.

CHECKING YOUR LINE VOLTAGE (For U.S. Military Market and Other Countries)

Before inserting the power plug, please check this setting to see that it corresponds with the line voltage in
your area. If it doesnt, be sure to adjust the voltage selector switch to the proper setting before operating this
equipment. The voltage selector switch is located bottom board.

11 (N0. 2717)

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4. Servicing Precautions

1. If the tonearm, motor or any other mechanical parts
were detached, disassembled or replaced, always per-
form check and adiustment of lead-in position.

2. Be sure to perform servicing related to motor revolution
only on a level surface.

3. As the rotor of the drive motor is magnetic, special care
must be taken not to contaminate the rotor during ser-
vicing by attracting metallic particles or the like.

4. The power cord is connected to the primary leads of the
power transformer by means of crimp-on terminals. If
this connection has to be removed, re-establish it only
with crimp-on connectors and confirm that secure con-
nection has been established.

5. For check procedures of the logic circuit, refer to
"Check Procedure of Main PCB") on page 1-11.

5. Technical Explanation

. 5-(1) Programmed Music Scan

As opposed to conventional designs, this unit does not use
a sensor incorporated into the cartridge, but employs a
separate sensor which moves in sync with the tonearm, as
shown in the illustration.

1 . Detector circuit

This circuit operates in the same way as described in 0p-
tical Detection in UP Position of the Service Manual for
model OLAE55 (No. 2665 Mar. 1983) published previous-

ly.

2. Music scanning

When the turntable is activated - except in the manual
mode - the tonearm and'sensor scanthe total record area
from the outside to the inside before playback, and the
position of the intervals (MARKER SPACE) between
musical tracks are stored in the microprocessor (by number
of pulses in the rotary encoder). During programmed
playback, these data are used to lower the tonearm at the
beginning of a designated track and lift it at the end of the
track.

1-5 (No. 2717)

6. This unit employs the lubricators and bonds specified
below.Be sure to use only the designated types.

Brand Application
Furoil ® Worm and worm gear teeth con-
GP-501A 1:1 Ratio tact area
Furoil Bearings on both sides of worm
BG-TS-l assembly

lKanto Kasei Col Gustand mesh section
Rack gear mesh section

Roller section at rear of tonearm

V-groove of loading guide

Furoil
(SP-608

White Grease
©

Shaft A, Shaft B

Tonearm

Fig. 1