Jvc MXG 880 V Service Manual

Page 2

MX-G950V/MX-G880V
MX-G850V/MX-G750V

-Safety Precautions

1. This design of this product contains special hardware and many circuits and components specially for safety

. Alterations of the design or circuitry of the product should not be made. Any design alterations of the product

. Many electrical and mechanical parts in the products have special safety-related characteristics. These

.The leads in the products are routed and dressed with ties, clamps, tubings, barriers and the like to be

. Leakage currnet check (Electrical shock hazard testing)

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.

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.

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 (AM 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.

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 reassembling.

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 9 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 (HavingiOOO
voltmeter. ohms/volts,

Move the resistor connection to each exposed metal part, 0"0'9 sens"'V"Yl

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 -"_ Place this
measurement.IVoltage measured any must not exceed 0.75 V w, . r , :gézeeigosed
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. chassis. Therefore, pay attention to

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.

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

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

Page 45

MX-G950V/MX-G880V
MX-G850V/MX-G750V

l LA1838 (IC1): FM AM IF amp & detector, FM MPX decoder
1. Block Diagram

30

1

29

2

2. Pin Function

28 27 26 25 24 23 22 21 20

REG

AM FM
MIX HF AMP

SD
COMP

AM
SVMETE

AM/FM
IFVBUFF
TUNING
DRIVE

DECODEH
ANITVBIRDIE

TEREO
5N

SW

vco FF FF n FF PILOT
384KH2 38k 19W IQkLS DET

STEREO
DFIIVE

Pin . Pin
No. Symbol l/O Function No. Symbol |/O Function
1 FM IN I This is an input terminal of FM IF 16 L OUT 0 Left channel signal output.
signal.
2 AM MIX 0 This is an DUI PUI terminal for AM 17 Ft 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 01 AM IF Signal. 19 Ft IN | Input terminal of the Flight 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 Q Mpx Left channel signal output.
becomes ""L.
7 STEREO 0 Stereo indicator output. Stereo "L", 22 MPX IN | 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
for AM
11 FM VSM O Adi-SI FM SD sensitivity. 26 AFC - This is an output terminal of voltage
for FM-AFC.
12 AM VSM O Adlust AM SD sensitivity. 27 AM RF | AM RF signal input.
13 MUTE l/O When the signal of IF REQ of IC121( 28 REG 0 Register value between pin 26 and pin28
LC72131) appear, the signal of FM/AM besides the frequency width of the
IF output. //Muting control input. input signal.
14 FM/m I Change over the FM/AM input 29 AM 080 - This is a terminal of AM Local
"H" :FM, "L" : AM oscillation circuit.
15 MONO/ST 0 Stereo : "H", Mono: "L" 30 OSC BUFFEFI 0 AM Local oscillation Signal output.

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