Philips CD304 MK II - Turntable Motor and Speed Checks; Detector Functionality Checks

7-4
Now the laser is burning continuously, FE has been re-
leased and the focus loop has been interrupted at test
point <> (= FE) on servo PCB, circuit diagram C.
Testing of circuit, between test point<1> and focusing coil
(Test points on servo PCB)
— Directly inject a sine-wave signal of 10 Hz, 2V,,, to test
point > by means of an AF generator (Z; < 600 2).
— Check visually whether focusing coil — and thus
objective too — responds.
— Check whether this voltage is 0.6 V,, on test point @.
"— Check whether this voltage is 6 Vp, on test point @>.
— Check whether this voltage is 5 V,, on test point 4.
‘Testing the subchassis (Test points on Pre Amp PCB, in-
jection point on servo PCB)
~~ Place a disc on the turntable,
-— Directly inject to test point » a sine-wave signal be-
tween 25 Hz and 60 Hz at 2 V,, by means of an AF
generator (Z; < 600 9). The exact frequency is player-
dependent. :
~~ Select such a frequency that the monitor diodes of the
light pin give output signals as indicated on test points
©, D ana ®.
— Check test points ®, >, <> and 2.
— Check test point {>.
— Check test point (>.
Is the same as signal on test point but amplitude is
dependent on position of potentiometer R3158.
If all the checks are positive, close focus loop (insert plug
24). Now the focusing circuit should be able to operate.
Reconnect transistor 6230.
It should be noted here that the amplitudes on test points©>
through <> are slightly dependent on the characteristic of
the monitor diodes.
Sub. E. IS TURNTABLE MOTOR RUNNING AND, IF SO,
IS IT RUNNING AT THE CORRECT SPEED?
Test method (Test points on servo PCB)
— Place disc on turntable and bring set in service loop A.
— If focusing point is found, check whether FCO is low on
point >.
If not, check focus circuit sub D.
If so, proceed.
— Now only power on, disconnect plug 25 on the servo
PCB and check MC= point 2 of cable connector 25 or
point & on_the decoder PCB see fiqure F.
If not, check DECODER CIRCUIT
If so, proceed.
— Reconnect plug 25, disconnect plug 15 on the pre-
amplifier PCB and inject a DC signal to the cable
connector of the motor or directly to the turntable
motor.
The turntable motor should be running now.
(A DC voltage of 2,5 V approximately corresponds with
the rpm during scanning of the innermost tracks).
In this condition the player should be brought in servi-
ce loop A (depress Stop button while mains voltage is
switched on).
lf DC < 2.5 V Figure G should be visible on test point
<> (servo PCB).
if DC > 2.5 V Figure H should be visible on test point
>.
CS 5 222 GB
If so, check turntable control circuit (circuit from point <>
to turntable motor).
lf not, check whether MCES is released by means of FCO
at pin 13 of IC6205C.
This can be done by disconnecting plug 25 on the servo
PCB and measure on point 2 of cable connector 25.
If MCES is working now, check circuit around IC 6205C.
— Reconnect plug 25.
— Take player out of service loop A, depress Power-on
button and then Play button and check eye pattern on
point €> (on decoder PCB).
To stabilize the eye pattern, bring light pin above tracks
by hand, or by briefly (5 s) depressing Fast Forward
button.
If eye pattern on point > is not present or unstable,
check RF pre-amplifier (see Annex V).
— If eye pattern is correct, proceed.
— Check whether point €5> (= HFLS) on the servo PCB is
correct in service loop A (see Figure Y). If not, check
HFLS detector circuit (is circuit between point €3>
and ). If so, proceed.
Take player out of service ioop A by depressing the
power button.
— Check locking-in of PLL circuit of decoder
nex II. Checking locking-in of PLL circuit.
If PLL is locking-in, proceed.
— If MCis still not functioning properly, replace the
relevant specific digital IC.
— MC has to be present now.
Sub. F. ARE THE DO AND HFLS DETECTORS
FUNCTIONING?
Test method (Tést points on servo PCB)
— Starting point is:
HFLS = 1 when spot is exactly on track
HFLS = 0 between tracks (e.g. during track jumping)
DO = 0,orDO=1 incase of drop-out
DO = 1, or DO =0 when there is no drop-out.
See An-
Approximative method
(applicable in service loop A)
— Place disc on turntable.
— Bring player in service loop A.
— Check whether DO (test point 6>
high". Normally test point > is , low”; however small
is not continuously
spikes of approximately 100mV are present in case
of scratches on the disc.
— Check HFLS (test point 63> ).