Pioneer DEH-P76DH, Service Manual

Page: 57 / 82

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DEH-P86DHR,P76DH
6.4 CHECKING THE GRATING
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Checking the Grating After Changing the Pickup Unit
• Note :
Unlike previous CD mechanism modules 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 mecha-
nism 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.
• 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 track searching taking a long time, may appear.
• Method :
• Measuring Equipment
• Oscilloscope, Two L.P.F.
• Measuring Points • E, F, REFOUT
• Disc • ABEX TCD-784
• Mode • TEST MODE
• Checking Procedure
1. In test mode, load the disc and switch the 5V regulator on.
2. Using the TR+ and TR- 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 adjust-
ment the display should now read "81". Press key 3 4 times. The display will change, returning to "81" on the
fourth press.
4. As shown in the diagram above, monitor the LPF outputs using the oscilloscope and check that the phase differ-
ence is within 75° . Refer to the photographs supplied to determine the phase angle.
5. If the phase difference is determined to be greater than 75° try changing the PU unit to see if there is any
improvement. If, after trying this a number of times, the grating angle does not become less than 75° then the
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 aver-
age angle.
• Hint
Reloading the disc changes the clamp position and may decrease the "wobble".
100k
Ω
390pF
100k
Ω
390pF
E
REFOUT
F
REFOUT
Xch Ych
Oscilloscope
L.P.F.
L.P.F.
CONTROL UNIT