PIONEER CX938 - Service Manual Immediate Download

Model

Service Manual

CD Mechanism Module

Mechanism Unit

CDX-P1250/X1N/UC,ES

CRT2318

CXK4900

CXB3008

CDX-P1250/X1N/EW

CXK4905

CXB3008

CDX-FM1259/X1N/UC

CRT2320

CXK4916

CXB3008

CDX-FM1257/X1N/UC,ES

CXK4915

CXB3008

PIONEER ELECTRONIC CORPORATION

4-1, Meguro 1-Chome, Meguro-ku, Tokyo 153-8654, Japan

PIONEER ELECTRONICS SERVICE INC.

P.O.Box 1760, Long Beach, CA 90801-1760 U.S.A.

PIONEER ELECTRONIC [EUROPE] N.V.

Haven 1087 Keetberglaan 1, 9120 Melsele, Belgium

PIONEER ELECTRONICS ASIACENTRE PTE.LTD. 253 Alexandra Road, #04-01, Singapore 159936

C PIONEER ELECTRONIC CORPORATION 1999

K-ZZU. FEB. 1999 Printed in Japan

ORDER NO.

CRT2357

CD MECHANISM MODULE

CX-938

- This service manual describes the operation of the CD mechanism incorporated in models listed in the

table below.

- When performing repairs use this manual together with the specific manual for model under repair.

CONTENTS

1. CIRCUIT DESCRIPTIONS ...........................................2

2. DISASSEMBLY .........................................................18

3. MECHANISM DESCRIPTIONS.................................23

CX-938

1. CIRCUIT DESCRIPTIONS

The LSI (UPD63710GC) used on this unit comprises five main blocks ; the pre-amp section, servo, signal processor,

DAC and CD text decoder (not used on this model). It also equips with nine automatic adjustment functions.

1.1 PRE-AMP SECTION

This section processes the pickup output signals to

create the signals for the servo, demodulator and

control.

The pickup output signals are I-V converted by the pre-

amp with the built-in photo-detector in the pickup, then

added by the RF amp to obtain RF, FE, TE, TE zero cross

and other signals.

This pre-amp section is built in the servo LSI

UPD63710GC (IC201). The following describes function

of each section.

Since this system has a single power supply (

+5V), the

reference voltage for this LSI and pickup are set to

REFO (2.5V). The REFO is obtained by passing the

REFOUT from the LSI through the buffer amplifier. The

REFO is output from Pin 89 of this LSI. All

measurements are done using this REFO as reference.

Note : During the measurement, do not try to short the

REFO and GND.

1) APC Circuit (Automatic Power Control)

When the laser diode is driven with constant current,

the optical output has large negative temperature

characteristics. Thus, the current must be controlled

from the monitor diode so that the output may be

constant. APC circuit is for it. The LD current is obtained

by measuring the voltage between LD1 and V

+5. The

value of this current is about 35mA.

AGCI

RFO

C-3T

FEO

FE-

TEO

TE-

RF-

EQ1

EQ2

AGCO

RFI

ASY

EFM

PEAK DET.

LPF

BOTTOM DET.

S/H

D/A

A/D

D/A

A/D

TE2

VREG

GND

APN

LDON

EFM

DEFECT

FOK

A3T

MIRR

To the

following stage

of the LSI

Vref

·····Vref(+2.5V)

VREG

GND

AMP_PN

(H:Nch L:Pch)

LDON

(H:LD MOVE L:STOP)

Vref

·····Vref(+2.5V)

R102

R101

Q101

2SB1132

C102

0.1

µF

C103

100

µF/6.3V

PU UNIT

R103

2.2k

C105

0.33

µF

+5V

110k

3pF

150k

100k

16k

Fig.1 : BLOCK DIAGRAM OF BUILT-IN RF AMPLIFIER

Fig.2 : APC CIRCUIT

CX-938

2) RF Amplifier and RFAGC Amplifier

The photo-detector outputs (A

+ C) and (B + D) are

added, amplified and equalized on this LSI and then

output to the RFI terminal as the RF signal. (The eye

pattern can be checked by this signal.)

The RFI voltage low frequency component is :

RFI = (A

+ B + C + D) × 3.2

RFI is used on the FOK generator circuit and RF offset

adjusting circuit.

R215 is an offset resistor for maintaining the bottom

reference voltage of the RFI signal at 1.5 VDC. The D/A

output used for the RF offset adjustment (to be

described later) is entered via this resistor.

After the RFI signal from Pin 77 is externally AC

coupled, entered to Pin 76 again, then amplified on the

RFAGC amplifier to obtain the RFO signal.

The RFAGC adjustment function (to be described later)

built-in the LSI is used for switching feedback gain of

the RFAGC amplifier so that the RFO output may go to

1.5

± 0.3Vpp.

The RFO signal is used for the EFM, DFCT, MIRR and

RFAGC adjustment circuits.

3) FOK Circuit

This circuit generates the signal that is used for

indicating the timing of closing the focus or state of the

focus close currently being played. This signal is output

from Pin 4 as the FOK signal. It goes high when the

focus close and in-play.

The RFOK signal is generated by holding DC level of the

RFI at its peak with the succeeding digital section, then

comparing it at a specific threshold level. Thus, the

RFOK signal goes high even if the pit is absent. It

indicates that the focus close can take place on the disc

mirror surface, too.

This signal is also supplied to the micro computer via

the low pass filter as the FOK signal and used for the

protection and the RF amplifier gain switching.

CN101

10k

FOK

CIRCUIT

A/D

A+C

16k

B+D

10k

16k

10k

R215

12k

C209 3pF

R214

10k

R207

1.8k

C208

27pF

R213

10k

D/A

12k

10k

RFO

AGCI

RFI

C207

0.22

µF

C206

3900pF

FOK

TO EFM

CIRCUIT

Fig.3 : RFAMP, RFAGC AND FOK CIRCUIT

5) Tracking Error Amplifier

The photo-detector outputs E and F are passed through

a differential amplifier and an error amplifier, and then

- F) is output from Pin 93 as the TE signal. The TE

voltage low frequency component is :

= (E - F) ××

= (E - F) × 5.7 (Effective LSI output is 5.0).

Using REFO as the reference, the TE waveform of

approximately 1.3 Vpp is obtained for the TE output.

The final-stage amplifier cutoff frequency is 20 kHz.

6) Tracking Zero Crossing Amplifier

TEC signal (the tracking zero crossing signal) is

obtained by multiplying the TE signal four times. It is

used for locating the zero crossing points of the

tracking error. The zero cross point detection is done for

the following two reasons :

1 To count tracks for carriage moves and track jumps.

2 To detect the direction in which the lens is moving

when the tracking is closed (it is used on the

tracking brake circuit to be described later).

The TEC signal frequency range is 300 Hz to 20 kHz.

TEC voltage

= TE level × 4

Theoretical TEC level is 5.2V. The signal exceeds D-

range of the operational amplifier and thus is clipped.

It, however, can be ignored since this signal is used by

the servo LSI only at the zero crossing point.

CX-938

Fig.5 TRACKING ERROR AMPLIFIER AND TRACKING ZERO CROSSING AMPLIFIER

4) Focus Error Amplifier

The photo-detector outputs (A

+ C) and (B + D) are passed

through a differential amplifier and an error amplifier, and

then (A

+ C - B - D) is output from Pin 91 as the FE signal.

The FE voltage low frequency component is :

= (A + C - B - D) ××

= (A + C - B - D) × 5

Using REFO as the reference, an S-curve of approximately 1.5

Vpp is obtained for the FE output. The final-stage amplifier

cutoff frequency is 11.4 kHz.

20k

CN101

10k

20k

A+C

16k

B+D

48k

16k

10k

D/A

80k

110k

C210 220pF

R208 300k

A/D

FE OFFSET

TO DIG. EQ

48k

38k

CN101

56k

38k

224k

48k

224k

56k

D/A

80k

110k

C211 100pF

A/D

TE OFFSET

TO DIG. EQ

48k

R216

27k

R215

27k

60k

20k

TE2

TEC

R212

C212

6800pF

16k

10k

(80k//300k)

20k

Fig.4 : FOCUS ERROR AMPLIFIER

224k

(56k

+27k)

80k

38k

CX-938

7) DFCT (Defect) Circuit

The DFCT signal is used for detecting defects on the

mirrored disc surface. It allows monitoring from the

HOLD pin (Pin 2). It goes high when defects are found

on the mirrored surface.

The DFCT signal is generated by comparing the RF

amplified signal (which is obtained by bottom holding

the RFO signal) at a specific threshold level by the

succeeding digital section.

Stains or scratches on the disc can constitute the

defects on the mirrored disc surface. Thus, as long as

the DFCT signal remains high in the LSI, the focus and

tracking servo drives are held in the current state so

that a better defect prevention may be ensured.

8) 3TOUT Circuit

The 3TOUT signal is generated by entering disturbance

to the focus servo loop, comparing phase of

fluctuations of the RF signal 3T component against that

of the FE signal at that time, then converting the signal

to DC level. This signal is used for adjusting bias of the

FE signal (to be described later). This signal is not

output from the LSI, thus its monitoring is not available.

9) MIRR (Mirror) Circuit

The MIRR signal shows the on track and off track data,

and is output from Pin 3.

When the laser beam is

On track : MIRR

= "L"

Off track : MIRR

= "H"

This signal is used on the brake circuit (to be described

later) and also as the trigger to turn on track counting

when jumping take place.

The MIRR signal is supplied to the micro computer, too,

for the protection purpose.

A/D

MIRR

CIRCUIT

DFCT

CIRCUIT

BOTTOM DETECT

PEAK DETECT

LPF

S/H

A/D

40k

20k

40k

200k

C205

0.1

µF

C3T

AGCI

RFO

12k

10k

20k

30k

MIRR

HOLD

Fig.6 : DFCT, MIRR AND 3T DETECTION CIRCUIT

Fig.7 : HOLD OUTPUT WAVEFORM

(When surface defects are present)

Fig.8 : MIRR OUTPUT WAVEFORM

(When an access is made)

Surface defects

RFI

HOLD

RFI

MIRR

OFF Track

ON Track