Pioneer CX-692 Panduan Servis - Halaman 6

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Halaman Cetak

CX-692

1.5 SERVO SYSTEMS

1.5.1 FOCUSING SERVO SYSTEM

The main equalizer for the focusing servo system is

being provided inside the servo DSP (IC401:TC9461F).

Fig. 7 shows the block diagram of the focusing servo

system.

With the focusing servo system, it is necessary to move

the leans into inside the focusing range to make focus

closing.

For this purpose, the lens is moved up and

down by the focus search voltage of the chopping wave

to find out the focusing point.

movement is in progress, the SPDL motor is being

kicked to maintain its speed to the preset speed.

The servo DSP works to monitor the FEI signals and the

SBAD signals (upper envelope of the RF) to issue

commands to execute automatic focus closing

movement at the optimum point.

executed when the following conditions are being

satisfied:

1) When the lens moves from "Near" -> "Far" as against

the disc

2) When the FEI signal level exceeds the prescribed

STANDBY level

3) When the FE becomes "0" (FE = "0", at the reference

voltage of 2.1V)

RF AMP

IC103

TA1254AF

FEO

Also, while this

Focus closing is

IC105

NJM3404AM

VR21

F ACT.

DRIVER

IC304

BA6797FM

When the SBAD stays beyond the SBREF level

continuously for 32mS after focus closing, the servo LSI

recognizes the focus closed state to raise the FOK port

of the microcomputer to the "H" level.

While if the SBAD stays below the SBREF level

continuously for 12mS after focus closing, the servo LSI

recognizes that the focus is lost to activate the resetting

process.

Meanwhile,

the

aforementioned SBREF level and STANDBY level

coincide the offset levels for respective signals (FEI and

SBAD) for the POWER ON state and for the LD OFF

(CONT = "L") state.

Fig. 8 shows the series of movements relevant to focus

searching and focus closing.

While a 2-layer disc of DVD is being handled, since the

reflectance is low, the focusing error signals will not

exceed the STANDBY level and focus closing is not

workable.

In such case, the FE level will be raised

through the OEIC and F-GAIN to start movement to

make the closing motion once again.

movement is not valid under the test mode, it is so

designed that the gain settings for 2-layer DVD discs

can be worked out manually.

F.JUMP

SERVO DSP

CIRCUIT

IC401

TC9461F

FEI

FOO

IC402

NJM2904M

VR21

reference

voltages

for

Since this

VR21

Fig. 7

the