Jvc RX 774 PGD Service Manual

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RX-774PBKlRX-774PGDIRX-774VBK 3

-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 (Al) 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.

. 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 areturn path to the chassis, to a known good earth ground. Any leakage
current must not exceed 0.5mA AC (r.m.s.)

. 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 9

mannetf Connect a 1,500 10W resistor paralleled Ac VOLTMETER

by a 0.15 F AC-type capacitor between an exposed EB (Having 1000

metal part and a known good eanh ground. Oth/VOHSY ..
Measure the AC voltage across the resistor with the ° "0? sensmvrty)
AC voltmeter.

Move the resistor connection to eachexposed metal (1151: AC TYPE

part, particularly any exposed metal part having a ---1|~-- place this
return path to the chassis, and meausre the AC probe on
voltage across the resistor. Now, reverse the plug in 1 0 0M1 0W ' each exposed
the AC outlet and repeat each measurement. voltage 5 9 mm?" Dam

measured Any must not exceed 0.75 V AC (r.m.s.). Good earth ground

- 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.

A CAUTION Burrs formed during molding may be left over on some parts of the chassis. Therefore,
pay attention to such burrs in the case of preforming repair of this system.

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FIX-774P/RX-774V

I LA1837(IC102): FM AM IF AMP&detector, FM MPX Decorder
1. Block Diagram

30 29

28

27 26 25 24 23 22 21 20

DECQDER

SD
COMP

S-CLRVE {EVE/m;

TUNING

PM
DET

ANIT

V00

SMKHZ

FF FF u
ask lax/E

FF PILOT
IQk/LS DET

1 2
3. Pin Function
Pin -
No. Symbol I/O Function 5': Symbol I/C Function
1 FM IN I This is an input terminal of FM |F 16 L OUT 0 Left channel signal output.
signal.
2 AM MIX 0 This is an out put terminal for AM 17 R OUT 0 Flight channel signal output.
mixer.
3 FM IF I Bypass of FM IF 13 L IN I Input terminal at the Left channel post
AMP.
4 AM IF I Input of AM IF Signal, 19 R IN I 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 IF IN I Mpx input terminal
Mono: 'H
B 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 oi AM ceramic filter. 25 AM AGC I This is an AGC voltage input terminal
for AM
11 FM VSM 0 film FM SD SEHSRIVIW- 26 AFC - This is an output terminal of voltage
Ior FM-AFC.
12 AM VSM 0 Adjust AM SD sensitivity. 27 AM RF I AM RF signal input.
13 MUTE IIO When the signal of IF REQ oi IC121( 23 REG 0 Register value between pin 26 and pin28
LC72131) appear. the Signal OI FM/AM desides the Irequency width of the
IF output. //Muting control input. input signal,
14 FM/AM | Change overlhe FM/AM input 29 AM 080 - This is a terminal ot AM Local
"H" :FM. 'L' :AM oscillation circuit.
15 MONO/ST 0 Stereo , Mono: L' 30 080 BUFFEF 0 AM Local oscillation Signal output.

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