Philips MCM279, Service Manual

5

EYE-PATTERN SIGNAL – JITTER MEASUREMENT

Measure the signal on the input of the Signal processor
using an 

analog

oscilloscope. Please find the exact

measuring point in your Service Manual.

See below examples of the signal. Amplitude should read at
least 700mVpp using SBC444A.

good

bad

If the oscilloscope shows a signal like the ‘bad’ one, and/or
the amplitude decreases within 1 minute - the CD drive has
to be replaced.

6

CD DRIVE – LASER CURRENT MEASUREMENT

The laser current can be measured as a voltage drop on a
resistor. The resistor is marked in every Service Manual.
The value depends on the type of CD drive.

typical value

most probably defect

VAMxxxx

: 150-230mV

≥

350mV

MCDxx

: 170-230mV

≥

300mV

DA1x

: 210-250mV

≥

350mV

DA2x

: 175-200mV

≥

250mV

Use SBC444A (CD-DA) for measurement.

7

CD DRIVE – OFFSET MEASUREMENT

The photodiodes of the CD-drive may have an offset. These
offsets have to be compensated by the signal processor.
High offsets can lead to poor playability of some CDs
(skipping tracks).

To measure the offset values, start the 

Service Test

Program

- section “Focus Test” without a CD.

The offsets can be measured with a DC Millivoltmeter
directly on the connector (see drawing below). Pin
numbering varies from drive to drive.

The values from diode A-D should read 0±10mV.
Diodes E and F are less critical.

If one of the offsets is higher than ±10mV the CD drive has
to be replaced. Otherwise replace the Signal Processor.

Sanyo DA12T3

CD Drive

A

A

F

C

B

E

C

D

E

VCC

B

VREF

F

D

9

10

11

12

13

14

15

16

1800

+5V_HF

VrefCD10

A

D

E

B

C

F

GND

8

E

D

A

B

C

F

Laser power control

100n

2878

470n

2876

3821

1R

1K

3823

2880

33p

+5V

BC807-40

7879

3817

47R

3820

4R7

47R

3819

1n

2879

2877

47u

1

8

4

7811-A

LM358D

3

2

10K

3822

47R

3818

2841

100n

47n

2869

+5V_HF

LASER DIODE

U >250mV

->Laser damaged !

4,6V

3V

3,3V

3,9V

2V

0,17V

0,17V

Sanyo

DA12T3

HF-Amplifier

D3

D2

D1

Drive detection

680R

3905

3903

3K3

BC847B

7877

47n

2818

1K5

3902

5

7

4

2

1

6

3

64

8

9

10

11

470R

3893

+3.3V

2K2

3908

10K

3923

BC847B

7878

BC847B

7876

4n7

2813

3896

100R

220u

2885

2881

560p

47n

2887

560R

3901

2883

470n

2817

4u7

3n3

2814

3898

220R

3895

27K

470n

2884

+3.3V

3909

820R

3907

100R

3920

33K

3897

2882

82p

3K3

3904

2K7

3899

3906

470R

+5V_HF

HFIN

VrefCD10

100p

2815

2816

22n

LD

ON

to 3826,3827

VREF GE

VDDA1

VRIN

VSSA1

ISLICE

LD

ON

D1

D2

D3

D4

HFIN

HFREF

IREF

CD_DA: 0V / CD_RW: 3V

Σ

 (A-D)

800mVpp

TB = 0.5

µ

s/div

EYE-PATTERN

1,8V

1,2V

2,4V

2,6V

0,65V

CD PLAYABILITY

 CHECK

1-4