Jvc RX 7520 VBK Service Manual

Page 2

RX-7520VBK

-Safety Precautions

1. This 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 (Q) 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 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, 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 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 1,500 Q 10W resistor paralleled by a 0.1511 F AC-type capacitor

between an exposed metal part and a known good earth ground. AC VOLTMETER
Measure the AC voltage across the resistor with the AC a (Having1000
voltmeter. ohms/volts,

Move the resistor connection to each exposed metal part, mm sens't'v'm

particularly any exposed metal part having a return path to
the chassis, and meausre the AC voltage across the resistor.

0.1511 F AC TYPE

Now, reverse the plug in the AC outlet and repeat each " P'agehis
pro eon

measurement.IVoltage measured any must not exceed 0.75 V W\, . each exposed

AC (r.m.s.). This corresponds to 0.5 mA AC (r.m.s.). 15009 10W metal part.

Good earth ground

Warning A CAUTION

1.This equipment has been designed and manufactured to meet international safety standards. Burrs formed during molding may
2. it is the legal responsibility of the repairer to ensure that these safety standards are maintained. be left over on some parts of the
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. such burrs in the case of

5. If mains voltage selector is provided, check setting for local voltage. preforming repair of this system.

chassis. Therefore, pay attention to

In regard with component parts appearing on the silkscreen printed side (parts side) of the PWB diagrams, the
parts that are printed over with black such as the resistor (u), diode (h) and ICP (.) or identified by the "A"
mark nearby are critical for safety.

(This regulation does not correspond to J and C version.)

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Page 18

RX-7520VBK

I LA1838 (IC102) : FM AM IF amp. & Detector, FM MPX decoder
1. Block Diagram

30

29 28 27 26 25 24 23 22 21 20 19 18 17

DECODER
ANITVBIRDIE

STEREO
5N
SW

1

2

2. Pin Function

AM/FM
IFVBUFF
TUNING
DRIVE

VCD

BBAKHZ

FF FF ,, FF
38k

PILOT

19W? le/LS DET

Pin P'
No. Symbol I/O Function NI: Symbol l/O Function
1 FM IN I This is an input terminal of FM IF 16 L OUT 0 Lelt channel signal output.
signal.
2 AM MIX 0 This is an out put terminal Ior AM 17 R OUT 0 Right channel signal output.
mixer.
3 FM IF I Bypass of FM IF 18 L IN I Input terminal of the Left channel post
AMP.
4 AM IF I Input of AM IF Signal. 19 R IN | Input terminal of the Right channel
post AMP.
5 GND - This is the device ground terminal. 20 R0 0 Mpx Right channel signal output.
6 TUNED 0 When the set is tunning,this terminal 21 LO 0 Mpx Left channel signal output.
becomes 'L".
7 STEREO 0 Stereo indicator output. Stereo "L' 22 MPX W I Mpx input terminal
Mono: "H"
8 VCC - This is the power supply terminal. 23 FM OUT 0 FM detection output.
9 FM DET - FM detect transformer. 24 AM DET 0 AM detection output.
10 AM SD - This is a terminal of AM ceramic filter. 25 AM AGC | This is an AGC voltage input terminal
Ior AM
11 FM VSM O Adiust FM SD sensitivity. 26 AFC - This is an output terminal of voltage
for FM-AFC.
12 AM VSM 0 Adjust AM SD sensitivity. 27 AM RF I AM RF signal input.
13 MUTE l/O When the signal of IF REQ of IC121( 23 REG 0 Register value between pin 26 and pin28
LC72131) appear, the signal 0f F'WAM besides the frequency width of the
IF output. //Muting control input. input signal.
14 Fin/W I Change overthe FM/AM inPUt- 29 AM 080 - This is a terminal oIAM Local
"H" :FM, "L" : AM oscillation circuit.
15 MONO/ST 0 Stereo : "H", Mono: "L" 30 080 BUFFER 0 AM Local oscillation Signal output.

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