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EN 142
9.
approximately 6 volts DC. This circuit is protected by fuse 1806
and resistor 3801.
The negative Horizontal pulse from Pin 5 feeds the Blanking
and Sweep failure detection circuit.
The output of 7807 together with 2831/3832/2832 generates a
sawtooth waveform for the class-D EW correction circuit. This
sawtooth waveform is fed to the comparator IC 7803 and
compare with the diode modulator input DM INPUT/EWO fed
by HOP IC. The class D output of the comparator drives
transistor 7802.
7802 drives EW coil 5807 together with 2820 and 5805 that
connected to diode modulator circuit that is part of the
horizontal output stage. The EW correction circuit driving and
output waveform is a parabola-like signal that required to
correct the geometry construction error of the tube mechanical
system.
Misc. components:
•
6813/3836: Gate protection and discharge for 7807.
•
3834/3835/2846: High frequency suppression to prevent
noise and small signal circuit damaging.
•
3837/2834: Snubber of 7807 switching pulses.
•
3826/3833: Preset level for EW class D comparator.
•
3827/2830: RC filter feedback EW corrector output to the
comparator.
•
3866/2810: RC filter for the supply +15V of EW class D
comparator circuit.
•
3824/3825: Pull up resistor and serial resistor of the EW
class D comparator circuit.
•
6825: Gate protection for 7802.
•
6827/2833: EW coil current discharge path to prevent high
surge occurring on 7802 drain.
•
2847: Surge suppression for 6827.
•
3829/3823: Feedback divider of EW correction circuit.
•
6821/6830/6832: Surge suppression of EW correction
circuit.
•
5805/2819: Tuning components of the diode modulator
circuit. The resonant frequency of these two components is
1/5.5us.
•
5804/6809/3808: Linearity coil and ringing suppression
components.
9.3.2
Line Output Transformer (LOT) 5801 and the Secondary
Supply
Note: Description below refers to diagram E3 (right upper part).
The line output transformer is using the switching and flyback
of 7801 to supply all the secondary supply such as video
+200V, Vertical Supply ±13V, filament voltage as well as the
horizontal blanking signal and the rest.
When 7801 is "on", 130VS apply on the primary of 5801 and the
LOT will supply the forward secondary output ±13V and
filament voltage. When 7801 is "off", 2818 and Yokes consist
as resonant circuit that induced Hflyback, the LOT will supply
the flyback supply +200V, 30V_clamp and the signals Neg-
Horiz_Pulse, Hblank.
LOT Secondary Output:
•
Filament: LOT pin6, rectified by 6801/2804 and protected
by 1806. Supply to CRT board for tube's filament. Value is
6.15 ± 0.15V. If Filament not available, set still can be "on"
but video will not display.
•
Neg-Horiz-Pulse: This is the flyback phase of filament
output. It is for protection of fault conditions that causing
horizontal pulse "low". If Neg-Horiz-Pulse is not available,
set will shut down and report critical error 61.
•
+200V: LOT pin7, rectified by 6802/2802 and protected by
3817. Supply to CRT board and protection circuit. If +200V
not available -> 7814 "on" -> HVG-ON "low" -> HVG "off" -
> -200V not available -> 7902 "on" and set will shut down
and report critical error 61.
EBJ1.0U
Circuit Descriptions, Abbreviation List, and IC Data Sheets
•
Hblank: LOT pin10, generated through 3802/6804. It is for
horizontal retrace period blanking. It is feedback to HOP IC
to blank the video during flyback. It is also for phase II
locking. If Hblank is incorrect, picture will be shifted
abnormally.
•
+13V: LOT pin14, rectified by 6805/2812 and protected by
1804. Supply to Frame IC for scanning positive supply. If
+13V is not available, top part of the display will be
clamped.
•
-13V: LOT pin16, rectified by 6806/2813 and protected by
1805. Supply to Frame IC for scanning positive supply. If -
13V is not available, bottom part of the display will be
clamped.
•
+30V_clamp: LOT pin13. It output and rectified through
6803/2808 to provide 30V for EW coil current discharge.
Protected by 3810.
9.3.3
Frame and Dynamic Focus
Frame
Note: Description below refers to diagram E3 (right lower part).
The frame IC circuit is using STV8172A the same as
HDPTV2K5. It is supplied by +13V and -13V for the scanning.
The flyback supply is generated by the STV8172A and the
external components 6811/2825.
The vertical yokes of the Red, Green and Blue tube are
connected in serial.
The vertical driving current source VDOA and VDOB is from
HOP through 3811 and 3812. 3813 and 3814 converted the
current source in to voltage and configured the IC into negative
closed loop. 3820 and 3821 is the current sensing resistor,
which determines the vertical scanning size together with 3813,
3814 and the source amplitude.
With this closed loop configuration, a current proportional to the
source is flowing through the yokes during scanning period.
During flyback period, the internal switch of STV8172A will
switch and apply the generated flyback supply to the yokes and
so the yoke current just retrace because of i= l * di/dt. Pin 3 is
switched to -13V during scanning period and 2825 will be
charged to 13V -(-13V) =26V. Just after flyback, pin 3 is
immediately switched to +13V, so the voltage at pin6 will
become 26V+13V=39V.
Misc. components:
•
2822/2823/2824: Noise suppression.
•
3819/3804/3805/3806: Horizontal yoke crosstalk
suppression.
•
3818/2828: Phase margin compensation for stability.
•
2826/2827: High frequency suppression on supply line.
•
6826/3815/3865: Vblank generating. Vblank is to blank the
video during vertical flyback.
Dynamic Focus
Note: Description below refers to diagram E3 (right middle
part) and diagram E4 (left upper part).
Due to the tube spherical electron beam scanning not matched
with the real flat display surface, the electron beam focusing
will be worse at the edge area compared with the center area.
Therefore, in addition to the static focus which is generic across
the whole display area, a dynamic focus is required
corresponding to the display location. It is so called dynamic
focus.
Dynamic Focus is taking the horizontal parabola waveform
from Scap 2816/2850 and vertical parabola waveform from EW
correction circuit. They are input to the dynamic focus amplifier
7901. Vertical parabola is injected to the emitter and amplified
at the collector. The horizontal parabola is directly coupled and
by transformer 5901 to 7901 collector. After that, the combined
parabola waveform will be input to the six-pack HVG (high
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