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LA76931

64Pin LA76931 for Color Television Receiver / SERVICE MANUAL

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Technical Note of LA76931

The BUS Control Functions of LA76931 (Tentative)

Register Name

T Disable

Bits General Description

1 bits Disable the Test SW & enable Audio / Video Mute SW

This is a Test Mode Switch, which is used in IC production (in case of using IC tester for measuring).

*If the bit of BUS is set as ‘0’, it becomes Test Mode. Then the test functions below will take active.

• Vertical Test

• Drive Test

• Contrast Test

Also, audio / video is muted forcedly.

*Usually, this bit is set as ‘1’ when the television is operating normally.

AFC Gain & gate

1 Select horizontal first loop gain & H-sync gating on/off

This function is used for keeping the stability of H sync. signal when there is no input signal or when a special

VCR signal (VCR AGC Micro-vision) is input.

0

= Automatic mode

There is a gate signal for 1st AFC gain control and sync signal to protect them from variety special signals and

guarantee the stability of horizontal output in all our products before. The level of the gain control can only be

set as HIGH, MIDDLE & LOW.

When “no input signal” (conditions are: no V sync and ‘H LOCK’ is unlocked) is detected, “LOW” mode will

be set to keep the horizontal deflection stable so that the H & V position of OSD will not be interrupted.

In addition, the improved operation of gain control and gating control in this IC contribute to stabilize

horizontal output of VCR signal in automatic mode.

1

= Enforce High Gain Mode (Gain = High, Gate = Non gate)

This mode is prior to pull-in operation, that’s why the stability is comparative weak. This mode is used when

tuning or some unexpected conditions.

H Freq.

6 Align ES Sample horizontal frequency

(MP is adjusted in the wafer line.)

Adjustment has done for mass production products. Although it’s no need any adjustment at TV production

line, set the register as “111111”. (But it needs adjustment at engineering sample stage).

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