BBK DV725SI, Руководство по обслуживанию

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After loader reads disc information, A, B, C, D, E and F signal are formed through photoelectric
conversion to MT1389 (DVD only has A, B, C, D signals) and RF signal and output from pin 2~11, 18, 19
of MT1389 respectively, after amplifying processing of pre-amplifier inside MT1389, now signals are
divided into 2 ways inside MT1389: one part, through summation amplifying and subtraction circuit
inside MT1389, produces servo error signal, after digital servo signal circuit processing, forms
corresponding servo control signals, outputs FOO, TRO, DMO and FMSO servo control signal from pin
42, 41, 37 and 38 of MT1389 respectively and then send to servo drive circuit for drive amplifying
through the integration circuit composed by resistor and capacitor and bring along focus coil, trace coil,
main axis electric machine and feed electric machine after drive amplifying. Among these, focus and
trace servo are used to correct objective position accurately; feed servo is used to bring along laser
head to make radial large-scale move which belongs to the preliminary adjustment to laser head position;
and main axis servo is used to control main axis electric machine to make it read signals in means of
constant linear velocity and bring along disc to rotate. After processing of amplification by VGA voltage
control amplifier and equalization frequency compensation inside MT1389, another part of signals are
changed into digital signals through internal A/D converter. When loader is reading CD/VCD signals,
these signals are conducted EFM demodulation inside MT1389, and then outputted to latter stage for AV
decoding after finishing CIRC (Cross-Interleaved Reed-Solomon Code) error correction inside. When
loader is reading DVD signals, these signals are conducted ESM demodulation inside MT1389, and then
sent to latter stage for decoding after finishing RSPC error correction inside. General DVD players have
a disc in/out circuit to control disc tray door in/out acts to reach the purpose of making disc in and out.
For PDVD, we adopt manual disc in/out means and we can judge whether disc in to proper position
through detect switch.
3. Explanation to servo terms
(1) FOO: for disc make differences, and when rotating disc may probably move upwards or
downwards slightly to make the focus of laser emitted by laser head cannot justly fall on data pit of disc,
now focus point of objective lens is required to adjust to make focus aim at data pit exactly. The acts are
mainly to make objective lens move upwards and downwards.
(2) TRO: data information is saved in disc in form of tracks. When disc is rotating, disc deviation will
produce, now laser head is required to adjust. In this process, objective lens makes forward and
backward movement with small moving range.
(3) FMO: similar to acts of trace, the acts of feed are larger than those of trace. Feed conducts a
large scale movement firstly, and then trace moves slightly in this range. Feed moves for a while, and
does not move for another while; but trace moves all the time. Feed is rough adjustment and trace is fine.
And acts are obvious when power on and selecting track.
(4) DMO: it is the top that holds up disc. Its rotation speed decides that of disc. Its rotation is
generated by an individual DC electric machine, in which rotation speed of DVD is twice over that of CD.
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