Clock Circuits - Hitachi DV-P250U Service Manual

Pulling the plug from the wall socket eliminates a short circuit and plugging in again restores the normal
state. When A-8V or A-20V output is short circuited, fuse F2 will open to protect circuit. When AC4.2V
output is short circuited, fuse F3 will open to protect the circuit. When this and A5V are short circuited,
fuse resistance R26 and R27 will open to protect the circuit.
For over current protection for A5V, destruction of zener diode by short will stop the output. The circuit is
protected in this way.
By pulling off plug from wall socket, eliminating short circuit, replace destroyed parts, and plug in again,
the normal state will be restored in its secondary commutate.

CLOCK CIRCUITS

27MHz X'TAL (X2203)
Block diagram for 27 MHz clock circuit is shown in Fig. 5-8-1.
When power is supplied to 27 MHz X'TAL, it generates 27MHz clock and input it to A/V decoder (IC1201),
video encoder (IC2202).
1. A/V DECODER
The A/V decoder is used as CLOCK VCK (input at pins 177 and 178) of video interface signal and output
digital video stream synchronized to VCK from 8bit video data bus VDATA[7:0] (output at pins 142, 143,
145, 148, 150, 152, 154, 155 )
2. VIDEO ENCODER
At video encoder it is used as system clock CLK (input at pin 48) and output horizontal synchronous
HSYNC (output at pin 14 ) and vertical synchronous VSYNC (output at pin 15) to A/V decoder.
3. Audio DA Converter
The audio external frequency clock signal DA-XCK is used as system clock. DA-XCK is supplied from A/V
decoder (output at pin 129 ), through IC1505 ( input at pin 1 and output at pin 4 ), then pass to Audio DAC
(input at IC1501~IC1504 pin 5).
IC1201: The DA-XCK is used to generates Audio bit clock DA-BCK (output at pin 167) and LR clock DA-
LRCK (output at pin 166).
DA-XCK
DA-BCK
DA-LRCK
* The Audio Interface Unit inside A/V decoder corresponds to sampling frequencies (fs) 44.1kHz (CD-DA,
Video-CD), 48kHz, 96kHz (DVD).
The frequency of DA-BCK is defined by Formula 1:
f DA-BCK = Audio data bit length * 2 * fs ...................................................................................................1
At A/V decoder, interior DA-XCK is divided into 8 equal parts and output as DA-BCK
(Formula 2)
f DA-BCK = f DA-XCK /8 ...........................................................................................................................2
Therefore, DA-XCX frequency takes the value 384fs according to formulas 1 and 2. Audio data bit length is
fixed 24bit. (Formula 3)
f DA-XCX = Audio data bit length * 2 * fs * 8 = 24 * 2 * fs * 8=384 fs.........................................................3
According to Formulas 2 and 3, A/V decoder drives DA-BCK
with frequency 48 times of sampling frequency. (Formula 4)
f DA-BCK =384fs/8 = 48fs..........................................................................................................................4
Chapter 1
Is interior clock used for generating DA-BCK and DA-LRCK. DA-XCK takes frequency 384
times the sampling frequency.
Is Audio bit clock obtained by dividing DA-XCK in 8 equal parts. It takes frequency 48 times
that of sampling.
Is clock that identifies channel (Lch or Rch) against all Audio sampling.
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