Goldstar MC-993A, Adjustment Instructions Manual

- 1 -

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Safety Precautions

1.  It is safe to adjust after using insulating transformer between

the power supply line and chassis input to prevent the risk of
electric shock and protect the instrument.

2.  Never disconnect leads while the TV receiver is on.
3.  Don't short any portion of circuits while power is on.
4.  The adjustment must be done by the correct appliances. 
5.  Unless otherwise noted, set the line voltage to 230Vac

!

10%,

50Hz.

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Test Equipment required

1.  RF signal generator (with pattern generator)
2.  DC Power Supply
3.  Multimeter (volt meter)
4. Oscilloscope
5. Color analyzer

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PIF (Picture Intermediate Frequency) Adjustment

1)  Connect the measuring equipment to the Main Board as

shown in Fig.1.

2) Set RF frequency and output level of RF SIGNAL

GENERATOR as shown Table 1.

3)  Turn off S1 and S3 and on S2.
4)  Adjust L107 so that the DC voltage may be 2.5

!

0.1Vdc.

(Table 1)

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SECAM-L' Adjustment

NOTE : This adjustment should be performed after PIF

adjustment.

1)  Turn on S1 and S3 and off S2.
2)  Adjust VR102 so that the DC voltage may be indicated

2.5

!

0.1Vdc.

O

RF AGC (Automatic Gain Control) Adjustment

The RF AGC control (VR101) was aligned at the time of
manufacture for optimum performance over a wide range
conditions. Readjustment of VR101 should not be necessary
unless unusual local conditions exist, such as ; 

1) Channel interference in a CATV system.
2) Picture bending and/or color beats, which are unusually due

to excessive RF signal input when the receiver is too close
to a transmitting tower or when the receiver is connected to
an antenna distribution system where the RF signal has
been amplified. In this case, the input signal should be
attenuated (with pad or filter) to a satisfactory level.

3) Picture noise caused by "broadcast noise" or weak signal.

If the broadcast is "clean" and the RF signal is at least 1mV

(60dBu), the picture will be noise free in any area.

Adjusting the VR101(RF AGC) control to one end of rotation
will usually cause a relatively poor signal to noise ratio;

Adjusting to the other end of rotation will usually cause a
degradation of over load capabilities resulting in color beats or
adjacent channel interference. For best results, adjust the
VR101 control while performing on all over local channels, or
the voltage at TP2 will be 2.3

!

0.1Vdc in RF level 65

!

1dBuV.

IC101

TDA4474

TP1

JP7 IC05

IC102

5V

JP3

S1

S3

S2

JP5

Q106

4.7k

Ω

100

Ω

100

Ω

24

7

11

15

VR102

1

0.01pF

Signal-
Generator

(B/G,D/K,I,L)

(SECAM-L')

JP1

L107

16

VR102

38.9MHz
34.25MHz

5V

Power-
Supply

V

Multimeter or Oscilloscope

JP2

JP4

Test Point 

: TP1

Adjust : 

L107

Test Point 

: TP1

Adjust : 

VR102

Frequency 

38.9MHz

34.25MHz

System

B/G,D/K/I,SECAM-L

SECAM-L'

Modulation

OFF

OFF

Output level

10mVp-p

10mVp-p

Adjust

L107

VR102

Main Board(Component side view)

Fig. 1 : Connection Diagram of Equipment for PIF Adjustment

ADJUSTMENT INSTRUCTIONS

Test Point 

: J209 or Observing Display

Adjust

: VR101