C.E.C. 780CD Service Manual page 13

ADJUSTMENT PROCEDURES continueg)
REQUIRED EQUIPMENTS
DC Voltmeter
Dualtrace Oscilloscope
Frequency Counter
Signal Generator
Plastic Screwdriver
Diffraction Grating Adjustment Jig
Test Disc (SONY: YEDS4, SANYO: MODERN WAVETZ)
CHECKING FOCUS ERROR SIGNAL
Checking the focus error signal of the pick-up allows for an
evaluation of the pick-up. Be sure this is carried out before
repair.
1. Turn on the power and set the unit to the STOP mode.
2. Connect an oscilloscope between jumper C001 (FE) and
GND. (Set the time axis to 0.5 seconds/division.)
3. Connect ROO3 (FOF) to GND.
4, Press the OPEN/CLOSE button and place the test disc
YEDS4 on the table load. Press the OPEN/CLOSE button
again.
5. The waveform shown below is displayed six times on the
oscilloscope when the table load closes. Check that the
p-p voltage is about 8V and that the top and bottom of
the waveform are symmetrical.
Repeated six times
(When recorded on a memory scope)
*p-p voltage of 8V
' *+ and — voltage roughly same
6. The waveform appears again if the OPEN/CLOSE button
is pressed again. This allows for confirmation to be made.
The pick-up is faulty if confirmation cannot be made.
SETTING OF INITIAL POSITION OF VOLUME
1. The variable resistors are set to the following initial
positions.
PO0O1 (FOCUS GAN) ...........:cceeeee eee ee Mechanical center
POOS (E-F BALANCE)...............000ee es Mechanical center
P004 (TRACKING GAIN) ...........2. eee Mechanical center
POOS: (VPLD) ies ccd cen ecesseecieeawececeees Mechanical center
POO6 (KICK GAIN) 2.0... cece ee ae eee ee eee Mechanical center
POOT (PLD: eivcavd ested a isteteladccwteaed Mechanical center
VOLTAGE PLL ADJUSTMENT
3. Adjust POO5 so that the DC voltmeter indicates 3.95V.
FREE RUN FREQUENCY ADJUSTMENT
1. Turn on the power and set the unit to the STOP mode.
2. Connect the frequency counter between jumper CK and
GND (use probes 10 : 1).
3. Adjust POO7 so that the frequency counter indicates
4.3218MHz.
FOCUS OFFSET CONFIRMATION
1. Turn on the power and set the unit to the STOP mode.
2. Connect a DC voltmeter and oscilloscope between jumper
FC and GND.
3. Short jumper FOF and GND.
4. Confirm that the indication on the DC voltmeter is -0.7 ~
-1.5V..
TRACKING OFFSET CONFIRMATION
1. Turn on the power and set the unit to the STOP mode.
2. Connect a DC voltmeter and oscilloscope between jumper
TC and GND.
3. Short jumper TOF and GND.
4. Confirm that the indication on the DC voltmeter is
-5OmvV ~ -—250mvV.
NOTE:
This adjustment should be made again after the
adjustment of Tracking Gain and E-F balance.