Service Hints - Philips MCM595/21 Service Manual

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 res-
pectively 200 - 220mV for CD-RW.
Laser power control
(example for DA2x drive)
U >250mV
->Laser damaged !
3820
+5V
+5V_HF
4R7
4,6V
3,9V 7811-A
3
8
LM358D
3,3V 3823 1
3V
7879
1K
2
BC807-40
2V
4
LASER DIODE
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 proces-
sor. 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.
CD Drive
Sanyo DA12T3
1800
16
VREF
VrefCD10
VCC 15
+5V_HF
E 14 E
E
E
13 D
D
D
B
A 12 A
A A
C
D
11 B
B
B
F
10 C
C
C
9 F
F
F
GND 8
If one of the offsets is higher than ±10mV the CD drive
has to be replaced.
10-2
0,17V
0,17V
WARNING
CHARGED CAPACITORS ON THE SERVO BOARD MAY DAMAGE THE CD DRIVE ELECTRONICS WHEN
CONNECTING A NEW CDM MECHANISM. THAT´S WHY, BESIDES THE SAFETY MEASURES LIKE
• SWITCH OFF POWER SUPPLY
• ESD PROTECTION
ADDITIONAL ACTIONS MUST BE TAKEN BY THE REPAIR TECHNICIAN.
The CD drive forms a compact building block with the CD Board.
The following steps have to be done when replacing the CD mechanism:
1. Desolder disc and slide motor
2. Loosen 2x screw
1. Disconnect flexfoil from old CD drive
2. Put a paperclip over contacts of flexfoil to short-circuit the contacts (fig.1)
3. Remove old CD drive
4. Mount new CD drive to CD board
5. Solder disc and slide motor after fixing the drive to the board
5. Move slide outside
6. Remove paperclip from flexfoil
7. Connect flexfoil to new CD drive
8. Remove ESD-protection (solder joint) from laserunit (see picture below)
Attention: The laser diode of this CD drive is protected against ESD by a solder joint which shortcircuits the
laserdiode to ground.
For proper functionality of the CD drive this solder joint must be removed after connection the drive to
the set.
10-2
fig.1