LG TCH-300 Service manual

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MAIN SECTION

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TOP VIEW

Drawing No. : 6870S-32KAA

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MAIN SECTION

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BOTTOM VIEW

Drawing No. : 6870S-32KAA

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FRONT SECTION

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TOP VIEW

Drawing No. : 6870S-32LAA

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BOTTOM VIEW

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TCH-300

ADJUSTMENTS

This set has been aligned at the factory and normally will not require further adjustment. As a result, it is not recommended that any attempt is made to modificate any circuit. If any parts are replaced or if anyone tampers

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with the adjustment, realignment may be necessary.

TEST & ADJUSTMENT POINT

.

L

t ,

I

T201 O ,"

\ 0

l_

0 0

J

IC201

I

IFM]

VR201

6

El

/

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Figure 1. Main PC. Board (Side A)

r

ORE

TP601 5

FEI FE0 00

TEI TEO

TPGM O"

0

REF

OS0

OGND

1

Figure 2. Main P.C. Board (Side B)

TCH-300 1

TUNER ADJUSTMENT

1. FM ADJUSTMENT

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Power Supply

- 01

STEREO SG

FM SSG

AUDIO OSC

1-n

FM Dummy ANT.

Figure 3. FM Adjustment Connection Diagram

(1) The impedance of FM antenna terminal is 7X&.

Therefore, connect coaxial cable (3C-2V etc.) between FM SG and antenna terminal when wiring.

\

Open indication OdB type Load or close OdB

indication type 54dB

(2) There are two kind in indication of FM SG output attenuator.

1) Attenuator with marking of 75Q open...open indication type.

2) Attenuator with marking of 75Q load or close . . . load or close indication type.

(3) FM SG output level in this FM adjustment are described as open indication type. The left table shows

relations among FM SG attenuator indication (dB), available power ratio (dBf) and antenna terminal voltage (dB/uV) in each indication type.

NOTE:

1. BAND Switch

2. BALANCE

3. TREB/BASS

4. Connect as shown in figure 3.

- 5. Refer to figure 1 & 2 for Adjustment Points.

FM SSG Available Antenna

Attenuator

Indication Ratio Voltage

60dB

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....~.

Power Terminal

52dBf 6 dB/pV

652dBf 66dB/uV

11.2dBf 12dB/uV

65.2dBf 66dB/uV

PRE OUT

11

-II

VTVM SCOPE

I II

/

.

FM Center Center

STEP SUBJECT

1 Discriminator 98MHz 60dB

No Dev. FM SSG

FM SEEK 98MHz, 22dBpV

2

STOP

225kHz Dev

FEED SIGNAL

FROM TO

ANTJack Between IC2Ol Pin 0 &

ANT Jack Between Point SD & point

MEASURE OUTPUT ADJUSTMENT ADJUST FOR REMARK

T201

Pin 0, DC Volt Meter.

VR201 DC1.6V+O.O5V

GND, DC Volt Meter

DC OV +lOmV

-8-

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CDP ADJUSTMENT

1. METER AND JIG FOR ADJUSTMENT

l-l. Oscilloscope

1-2. Test disc

TCH-300

1-3. Jitter meter

(Sony type 4: YEDS-43)

1-4. Low frequency oscillator

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1-7. Focus & tracking gain adjustment jig

A. F OSC

04

0 0 0 F

CH I - 2 SWI-2 1 I

oe

0 0 F

SWI-1 0

0

1-5. Digital frequency counter

T

w

22K

56K

1 OOK

0.0047(M)

12K

\ I

0

J

1-6. 10: 1 Oscilloscope probe

1: 1 Oscilloscope probe

TP602

TEI FEI

REF

GND

TEO

CH - 1

F

NOTE : This jig is not serviceable part.

22K

-9-

10K

0

FE0

s

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TCH-300

2. Before adjusting, preset adjustment potentiometers VR601, VR602, VR603 and VR604 center.

3. E-F BALANCE ADJUSTMENT

(1) Connect the oscilloscope to TP602 (TEO and REF). (2) Load test disc (YEDS-43). (3) Adjust VR602 so that amplitude above and below the zero DC line becomes equal (amplitude A=B).

Oscilloscope

k REF

4. FOCUS

(1) (2) (3) (4)

OFFSET ADJUSTMENT

Connect the jitter meter to TP601 (HF, REF), set the input selection switch of jitter meter to “1 x ” position. Load test disc. Put unit play mode. Adjust VR601 so that the jitter meter reading is minimum.

Jitter Meter

NOTE: Jitter meter must have a “1 x

input selection switch.

A=B

A

OV DC Mode

B

“

-IO-

TCH-300

5. FOCUS GAIN ADJUSTMENT

(1) Connect from gain adjustment jig to wire on the main P.C. Board pin to pin. (2) Connect audio frequency oscillator to A.F. OSC terminal and GND on the gain adjustment jig.

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Set the audio frequency oscillator output to 750Hz, ~VRMS.

Low Frequency Oscillator (A.F. OSC)

@@O A.F. OSC

L

GND

(3) Connect oscilloscope to CHI, CH2 and GND on the main P.C. Board. (XV mode)

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Oscilloscope

I-O GND

Insert test disc and put unit play mode on track.

(4)

Set switch SW1 on the gain adjustment jig to position

(5)

Adjust VR603 so that the waveform on the oscilloscope looks as shown below.

(6)

Good adjustment

(Optimum focus gain)

Bad adjustment

(Low focus gain)

“F”.

CHI : 20mV/div. AC MODE CH2 : 2V/div. AC MODE

Bad adjustment

(High focus gain)

-ll-

( TCH-300

6. TRACKING GAIN ADJUSTMENT

Connect from gain adjustment jig to wire on the main P.C. Board pin to pin.

(1)

Connect audio frequency oscillator to A.F. OSC terminal and GND on the gain adjustment jig.

(2)

Set the audio frequency oscillator output to 750Hz, ~VRMS.

Low Frequency Oscillator (A.F. OSC)

Connect oscil

Insert test disc and put unit into play mode on track.

(4)

Set switch SW1 on the gain adjustment jig to position

(5)

Adjust VI3604 so that the waveform on the oscilloscope looks as shown below.

(6)

I oscope to CHI, CH2 and GND on the main P.C. Board (XV mode)

CHI : 20mV/div. AC MODE

Oscilloscope

CH2 : 2V/div. AC MODE

“T”.

(Optimum tracking gain)

(Low tracking gain)

-12-

Bad adjustment

(High tracking gain)