Philips FW-M589, Service Manual

Page: 71 / 91

10-3
4. MEASURE THE LASER CURRENT
CD DRIVE – LASER CURRENT MEASUREMENT
The laser current can be measured as a voltage drop on
resistor 3820. Typical value 170 - 190mV for CD-DA
respectively 200 - 220mV for CD-RW.
5. MEASURE THE OFFSETS OF THE CD-DRIVE
CD DRIVE – OFFSET MEASUREMENT
Each photodiode of the CD-drive may have an offset.
This offset has to be compensated by the signal
processor. A high offset of the CD-drive leads to poor
playability of some CDs (skipping tracks).
Start the Service Test Program - section „Focus Test“
without a CD. Focus sensitivity = CD-RW.
Use a DC Millivoltmeter for measurement. The offsets
can be measured direct on the connector. See drawing
below.
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.
6. MEASURE THE OFFSETS OF THE CD10
SIGNAL PROCESSOR – OFFSET MEASUREMENT
Each ADC input of the CD10 may have an offset too.
Also this offset leads (together with the offsets of the CD
Drive) to poor playability of some CDs (skipping tracks).
Start the Service Test Program - section „Focus Test“
using a CD-RW disc.
Use a DC Millivoltmeter for measurement. The offsets
can be measured on capacitors near the signal
processor. See drawing below.
The value should read 0mV±10mV.
If one of the offsets is higher than ±10mV the signal
processor has to be replaced.
If none of the measured offsets is higher than ±10mV -
replace the part with the higher value.
3 4 5
CD Board side A view
Signal Processor
E F D C A B
V
REF
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
Service Hints