Sharp DV-500D, Technical Manual

Page: 25 / 117

25
DVD-Series
4-3 Automatic Adjustment
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Automatic adjustment is executed every time the disc changes. (7 to 8 seconds later)
Why? Because
_
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reflection rates, etc. differ on different discs
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it absorbs laser power, PD, an optical system changes with the passage of time, etc.
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of the need to decrease adjustment at the time of production
The Following Adjustments are Actually Executed
1. Offset Adjustment
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While the light doesn’t return the laser condition, the laser and adjusts the TES and FES to
a standard voltage.
(It revises the electric offset on error formation circuits)
2. Focus Bias Adjustment
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If there are differences in the reception of the PD as shown, even if the focus on the disc is
at optimum condition, error signals do not become “0”.
Therefore, bias is added to the FES signal, then the RF amplitude signal reaches its
maximum, or zitta seeks the best bias voltage to achieve a revised bias voltage.
Big output Small output
+
–
Error does not become "0"
3. Tracking Balance Adjustment
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Similarly, in tracking, error “0” level revisions are made.
When rotating the disc in the Focus Servo “ON”, Tracking Servo “OFF” and Thread Servo
“OFF” modes, TES shows up due to the polarized core of the disc. Revise it to make the
voltage of the half of the p-p value to be error “0”.
0V
Sign
FES
+
–