DEX-P99RS/UC
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8.2 CHECKING THE GRATING AFTER CHANGING THE PICKUP UNIT
CD CORE UNIT
Note :
The grating angle of the PU unit cannot be adjusted after the PU unit is changed. The PU unit in the CD mechanism
module is adjusted on the production line to match the CD mechanism module and is thus the best adjusted PU
unit for the CD mechanism module. Changing the PU unit is thus best considered as a last resort. However, if the
PU unit must be changed, the grating should be checked using the procedure below.
Purpose :
To check that the grating is within an acceptable range when the PU unit is changed.
Symptoms of Mal-adjustment :
If the grating is off by a large amount symptoms such as being unable to close tracking, being unable to perform
track search operations, or taking a long time for track searching.
Method :
Measuring Equipment
Measuring Points
Oscilloscope, Two L.P.F.
E, F, REFO1
Disc
TCD-782
Mode
TEST MODE
1. In test mode, load the disc and switch the 3 V regulator on.
2. Using the -> and <- buttons, move the PU unit to the innermost track.
3. Press key 3 to close focus, the display should read "91". Press key 2 to implement the tracking balance
adjustment the display should now read "81". Press key 3. The display will change, returning to "81" on the
4. As shown in the diagram above, monitor the LPF outputs using the oscilloscope and check that the phase
difference is within 75 degrees. Refer to the photographs supplied to determine the phase angle.
5. If the phase difference is determined to be greater than 75 degrees try changing the PU unit to see if there is any
mechanism should be judged to be at fault.
Note
Because of eccentricity in the disc and a slight misalignment of the clamping center the grating waveform may be
seen to "wobble" ( the phase difference changes as the disc rotates). The angle specified above indicates the
average angle.
Hint
Reloading the disc changes the clamp position and may decrease the "wobble".
100 kohm
390 pF
100 kohm
390 pF
E
VREF
F
VREF
Xch
Ych
L.P.F.
L.P.F.
Oscilloscope
F
E
REFO1
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