Philips MCM279, Руководство по обслуживанию

Страница: 5 / 30

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