PHILIPS MCM590
Instrukcja Serwisowa

Service Hints
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.
3818 47n 47R

10-3

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.

Laser power control
2876 U >250mV ->Laser damaged !

1R 47u

3820 2878 +5V 100n 4R7 3822

+5V_HF 470n 3821 2877

2841

3817

3819

47R

100n

The value should read 0mV±10mV.
4,6V 3 0,17V

3,9V 3,3V 7879 BC807-40 47R

10K 7811-A 8 LM358D 3823 1 1K 3V 4

CD Board side A view

2 2879 2880

LASER DIODE

2V 2869

0,17V 1n 33p

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.
B VREF A C D F E
Signal Processor

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

3

4

5

CD Drive Sanyo DA12T3
VREF VCC E
E B C D F A

If one of the offsets is higher than ±10mV the signal processor has to be replaced.

1800

16 VrefCD10 15 14 13 12 11 10 9 8
E D A B C F

If none of the measured offsets is higher than ±10mV replace the part with the higher value.

+5V_HF E D A B C F

D A B C F GND

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