ELECTRICAL MEASUREMENTS AND ADJUSTMENTS
Laser power supply
Since the light pin is very sensitive to static charges, care
should be taken that during measurements and adjust
ments of the laser power supply the potentia Is of aids and
yourself equal the potential of the CD mechanism.
+12V
+t2V
C5V,
TO A'72
--
-
TO A'6
2
A26
1
34 530 A'2
Check
The laser simulator PCS nr. 3 (4822395 30229) should be
used here.
Take the flex PCS out of socket A 11 and connect the
switch simulator PCS with the socket.
Remove plug A 16 and insert it in the socket on the
simulator PCS.
Connect the plug with 4 wires to socket A16. Take out
plug A17 and insert the plug with 1 wire in socket A17.
Set the switch on the simulator PCS in the OFF position
and the mains switch in the ON position.
Turn trimming resistor 3140 clockwise (max. R) and
measure the voltage between points +V and -V on the
simulator PCS.
The voltage should be
�
15 mV.
Check
of
laser supply control:
Set the switch on the simulator PCS in the ON position
and measure the voltages between points +v and -v on
the simulator PCS.
Resistor 3140 clockwise (max. R):
U
+v -v
=
225 mV
±
45 mV.
Resistor 3140 counterclockwise (min. R):
U
+v -v
=
750 mV
±
150 mV.
Set resistor 3140 in mid-position.
This is a preliminary adjustment. After the simulator PCS
has been removed the laser current must be adjusted.
(see service manual CD player).
Adjusting the focus bandwidth
(see service manual CD player).
Checking the AGC and offset circuit
(see service manual CD player).
Motor-control check (Hall)
Remove connector A09 from the motor PCS on the
CDM.
2 Connect channel A of a dual-beam oscilloscope to the
emitter of transistors 6082,6083 and channel S to the
emitter of transistors 6084, 6085.
Position of oscilloscope: 2 V/div - 10 ms/div.
3 Connect pin 1 of connector A09 on the motor PCS to
the ground of the set.
4 Switch the set on.
5 Apply a
negative
voltage to pin 2 of connector A09.
The voltage may
not
be applied until
after
the circuit
has been connected to power supply voltage. Start
from 0 V and slowly proceed to -5 V. Now the motor
should run.
When the motor runs the voltage can be brought to
approx -2.5 V. The motor should continue to run
then.
6 The oscilloscope should display sinus(
signals now
(see Fig. A).
After approx 2 s they should lie symmetrically round
the O-axis and be shifted 90° relative to each other.
The maximum ratio of the amplitudes of these 2
signals is allowed to be 1 :2.
7 The amplitude depends on the applierJ voltage.
The V-inN-out pp ratio should lie between 1:2 and.1 :3.
8 Determine at which V-in the motor runs at 600 rpm.
At 600 rpm the frequency of V-out is 30
Hz.
At this speed V-in should lie between -1.5 V and 3.7 V.
Conclusion:
When all these conditions are present motor and PCS
may be considered in order.
If points 5, 6 and 7 are not correct, the fault should most
probably be found in the electronics.
If points 5, 6 and 7 are correct and the voltage to be
applied at point 8 is e.g. -4.5 V to obtain a motor speed of
600 rpm, there will most probably be something wrong
mechanically. E.g. the bearing friction is too high.
v
v
35 181 A 20
Fig. A
