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PVM-20M7MDE
SECTION3
CIRCUIT DESCRIPTION
3-1. A (1/4) Board (page 1)
This monitor can receive the video signal of both
fH::
15.625kHz
and fa= 31.25kHz. The input video signal (PAL and others) of
fu
=
15.625kHz
is
DOUBLE SCAN-converted
at the B board
which is the signal offu
=:
31.25kHz, and displayed on CRT screen.
The
signal offH
=
15.625kHz is abbreviated as.15.K,
the
DOUB LB
SCAN-converted
1iK
signal as
.EE
(Flicker Free) and the input
signal having
fH
=
31.25kHz from the beginning as llK in this
section of circuit description,
Page 1 shows the signal processing circuit of ,UK, and the
respective sync separator circuit of
ill
and
llK..
IC 10
(CXD2024AQ) is a digital comb
filter
operating on the 4 fscclock
which is also used in the chroma decoder of IC13 (M51279FP).
If the signal at TP20 (VCXO) is not output at the frequency of 4
fsc, no output comes out from
ICIO
pin@(Y.
OUT). CPl
is the
PAL
UN
separator. ICl 1 (MM1231XFF) switch 5 is the switch
selecting either the LINE NB signal or the ROB/COMP A/B
signal, and sends the pin@ output to the sync separator circuit
IC6 (MMl 11 l~FF). The !Cl I outputl.5.K is amplified and sent
totheBboard.
3-2. A (2/4) Board (page
2)
Page 2 shows the signal processing circuit for
.3.1.K
and EE, IC 1005
(MM1231XFF) SW. 6
is
the selector switch which selects either
the EE output signal from the B board or the
J.lK
output signal
from the
Q
board (input/output terminal board).
If
the RGB mode
is selected, the selected signal is sent to IC1015 (MM1231XFF)
SW.7 directly. The component signal (including video and YIC)
is sent to
the
chroma volume control circuit, aperture circuit and
tothematrixcircuiL
IC1022 and IC1023 (CXA1521M) constitute the chroma volume
control circuit. The delay lines DL1001 and DL1002, and the
related transistors form the aperture circuit. The output signal of
theaperturecircuitisbufferedbyQ1036andaddedtotheYsignal
through R1116. IC1007 andICIOIO (CXA1211M) are the video
volume control which determines the matrix gain. ICI008 and
IC1009 (MC14066BF) are the clamp circuit.
The transistors
QIOI6, Q1035 and Ql043 are the additive
operation transistors which convert the component signal to the
ROB matrix signal. IC1016 (CXA1739S) controls
the
auto white
balance, contrast, brightness and aperture. It switches the OSD
(On
Screen
Display)cbaracters. IC1003 (MC74HC158BF) SW.9
sele.ctseitherthefEsyncorJ.!KsyncSlgnal.
theselectedsyncis
sent to IC2013 (page 3). The output signal from IC1016 (R. G.
B)areinputtotheCboard.
3-3.
A (3/4) Board (page 3)
Page 3 bas the control CPU and the small signal processing circuit
of the deflection system. IC2003 (control CPU) is the heart of
this monitor having the functions such as system identification,
nonvolatile RAM control, key scan, remote identification and
peripheral control. The system identification is performed by
observing the signal frequency
at pin
®
(2H. SYNC), and
identifies if the signal is 15K or
llK.
Result of identification
controls ICIOOl pin®
(FF/PROO).
Then
the
system is identified
by observing the signals at pin© (v. sync) and pin @(INTER/
PROO). In accordance with the result of system identification,
the appropriate data from pin@ and CLK from pin@ are sent to
the peripheral devices
The peripheral devices are such devices
as the e,i;tended shift register (IC1001), the electronic volume
control (IC1002, IC1011, IC2015),
the
deflection
signal
generator
(IC2010), the OSD CPU (IC2014) and others.
As
long as the CPU operates normally, the clock signal appears
at pin
@ PIC and the positive polarity pulse of almost V rate
appears at pin @ (watch dog timer), with pin
@ being set to H.
IC2005 and IC2006 are the nonvolatile RAM in which the default
and user adjustment data are stored. The RAMs communicate
with the CPUilirough UC blls.- ic2008 (CXAi4'7b-AM) gelleraies
sawtooth wave and parabola wave.
IC2010 (CXA8021M)
performs addition and multiplication of the waveforms generated
by IC2008 under the control of CPU, and generates the deflection
base waveform such as pin@
(V. DEFL) signal.
IC2013
(CXA1543M) is the HIV oscillator generating the HD and VD
signals which are the reference timing of the deflection system.
3-4. A (4/4) Board (page 4)
Page 4 has the horizontal pin distortion correction circuit, high
voltage control circuit. high voltage output circuit, audio circuit,
LCC (landing correction circuit coil) circuit, protector circuit and
video pre-amplifier circuit. IC3003 (CXAI544M) is the PWM
(Pulse Width Modulation) controller for horizontal pin distortion
correction and high voltage control. Q3031 is the high voltage
output transistor. IC3009 is the output amplifier for LCC circuit.
IC3030 is the +B JX)wer supply switch which is turned on and off
by the PWM controller output in order to maintain the HV (high
voltage)
at a constant voltage. IC3007 is the high voltage
protector
and the IK protector.
If
Q3031 (HV OUT) is broken to cause
short circuit, Q3030 and R3164 could be broken at
the
same time.
-19-
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