Philips CD304 MK II - Page 35

Method
Self-check of the servo uP
— Disconnect points 2, 3 and 17 of the display pP.
~ Interconnect pins 6, 14, 18 and 21 of the socket of
the servo pP.
— lf the uP functions properly, pin 22 should go from
"0" to 1” within 1 second after switch-of on the
mains voltage.
Self-check of the display uP
Take the servo uP out of its socket and ensure that
points 2, 3 and 17 of the display pP are connected.
. — Interconnect pins 6, 14, 18 and 21 of the display pP.
~ If the pP is functioning properly, pin 22 should go
from ’’1"' to 0” within 1 second after switch-on of
the mains voltage.
Periferal check
Place disc on turntable and switch off mains voltage.
Initiating service loop A
See to it that the tray print is mounted or that, when the
tray is closed, the tray-end switch (SK2) on that print is
closed.
Keep the keys CANCEL, PREVIOUS and STOP depres-
sed during switch-on of the mains voltage. Release the
keys after approx. 2 seconds.
Now the set is in SERVICE LOOP A.
In this situation the laser and the focus control are
operative and the turntable motor is running. The light
pen remains situated against the innermost stop (i.e.
the light pen remains situated under the lead-in tracks).
The radial servo system is switched off.
In this service loop the display can be checked as
follows: :
— The display will indicate 01.02, then 02.04, next 03.06
and so on up to 20.40.
20.40 is followed again by 00.00, 01.02, etc.
The indicators SCAN, PAUSE, REPEAT and DISC
ERROR will light up and will remain switched on.
At indication 01.02, bar 1 of the track bar is driven as
well. At 02.04, bar 2 is driven, etc.
— If now the CANCEL key is depressed, the TRACK
indicator will light up after 2 clock strokes of the
display and the DISC ERROR indicators will go off.
The set remains in service loop A.
Initiating service loop B
The set can be brought from service loop A into service
loop B by depressing the STORE key.
The display shows that the set is in service loop B by
means of TIME ABS, REL and TOT.
Now the radial servo system has been switched on
independently of the P-bit and the sub-code.
After approx. 1 min. music will be audible.
This time depends on the length of the lead-in track.
When the light pen is brought under the music track by
hand, music is audible immediately.
The display remains in the service loop.
From service loop B the player can be brought in the
PLAY mode by depressing the START/REPLAY key. If
the START/REPLAY key is operated when the display
shows a musical number that is not present on the disc,
the set will stop.
f. Eye pattern
Check on the oscilloscope whether the H.F.-signal —
called eye pattern.
Set for this purpose the time basis of the oscilloscope to
0,5 ws and check test point & (on the decoder PCB).
CS 5 220 GB
This picture is fairly stable if PLL circuit is in lock and
turntable loop is controlling correctly.
A vibrating or unstable eye pattern can be caused by a
poor turntable motor, or by bringing the set in service
loop A.
DETAILED TROUBLESHOOTING METHOD
A number of quick and efficient checks immediately give a
definite answer on poorly functioning sections of the
player.
To check the servo systems two service loops have been
built in uP 6201.
Before calling in service loop A or service loop B, it should
be checked (position power on) whether the bus (clock,
data; pin 3 and 2 of uP 6201 resp.) is free. In other words,
checking whether these lines do not have a short circuit to
ground or supply voltage (level low or ,,high”). In such a
case the buttons cannot be operated.
For troubleshooting the step-by-step method below is
followed.
First step (with disc on turntable)
Bring the player in service loop A.
If one of the conditions for service loop A is not met,
the questions below should be answered positively
in the sequence given.
Mostly this means that when one question has been
answered positively, all the preceding circuits, to
which the questions refer, are functioning well.
Example: if the eye pattern is present, we may conclude that
the laser is working, the laser is in focus and that the
turntable motor is running.
Note:
In some situations, certain faults in the radial servo circuit
affect the focus servo circuit (e.g. if supply voltage +1 of
1C6214 in the radial circuit fails, the focus coil starts
oscillating).
To determine if this situation exists, connect point on
the servo PCB to ground.
In this way, the influence of the radial servo circuit on the
focus servo circuit can be eliminated.
A. Is the laser giving light?
(Test method: see sub A).
B. Is the angle disc-light pin within the tolerance, i.e. 90°
+0,5°?
(Test method: see description mentioned in chapter
"Mechanical measurements and adjustments” of the
C.D.M. manual).
C. Is the laser giving sufficient light?
(Test method: see sub C).
D. Does the objective come in focus?
(Test method: see sub D).
E. Is the turntable motor running and, if so, is it running at
the correct speed?
(Test method: see sub E).
If the answers to questions A through E are positive, it
should be possible to bring the player in service loop A.
Second step (with disc on turntable)
Bring the player in service loop B.
This means that the eye pattern on point & (on the de-
coder PCB has to be stable, while MCES on point > onthe
servo PCB has to be more stable too).