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
+12V
C5V1
TO A142
�:
A26
1
1
36785
A12
Check
The laser simulator PCS nr.
4 (4822 395 30244)
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
13
and insert it in the socket on the simulator
PCS.
Connect the plug with
4
wires to socket A13. Take out plug
A14
and insert the plug with
1
wire in socket A14.
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 mea
sure the voltage between V and -V on the simula
tor 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.
R3140
counterclockwise (min. R):
U +v -v
=
750
mV
±150
mV.
Set resistor
3140
in the 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).
11
Motor-control check (Hall)
3
1984-10-10
1.
Desolder the wire from point
C152
on the preamplifier
printed panel on the C.D.M.
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.
Switch the set on.
4.
Apply a
negative
voltage to the wire desoldered.
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.
5.
The oscilloscope should display sinusoid 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 amplitude of these
2
signals is
allowed to be
1 :2.
6.
The amplitude depends on the applied voltage.
The V-inlV-out pp ratio should lie between
1:2
and
1 :3
.
7.
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
4, 5
and
6
are not correct, the fault should most
probably be found in the electronics.
If points
4,5
and
6
are correct and the voltage to be applied
at point
7
is e.g.
-4.5
V to obtain a motor speed of
60
rpm,
there will most probably be something wrong mecha
nically. E.g. the bearing friction is too high.
v
v
35181 A 20
Fig. A
CS
98 649
