Table Of Contence
1. Understanding the Horizontal deflection circuit.
1.01 The primary function
1.02 VCO (Voltage Controlled Oscillator)
1.03 Horizontal Count down
1.04 PH1 or AFC1
1.05 PH2 or AFC2 f
1.06 Horizontal driver
1.07 Horizontal-output
1.07.1 HOT (Horizontal Output Transistor)
1.07.2 Capacitor ressonat
1.07.3 Damper Diode
1.07.4 Horizontal linear coil
1.07.5 Capacitor “S”
1.07.6 Kink correction
1.07.7 Horizontal def yoke
2. Generating anode flyback high voltage
2.01 Horizontal retrace.
2.02 High Voltage diode rectified
2.03 The advantage with the use of high frequency to generate high voltages
2.04 Another functions of flyback pulses
3. Understanding the EW correction circuit (Pin Cushion)
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1. Understanding the Horizontal deflection circuit.
1.01
The primary function of the horizontal deflection circuit is to
generate the horizontal deflection pulses fed to the horizontal
deflection coils. By this pulses sawtooth-shaped current flaws through
the horizontal deflection coil and used to control the picture tube
electron beam to make horizontal sweeping (scanning) from the left
towards the right side of the screen. Voltage pulses of horizontal is
fed directly from HOT (Horizontal Output Transistor) to the deflection
yoke.
The second function is to generate high voltage for the picture tube
anode. When current finish sweeping picture of a horizontal lines from
left to the right of the screen then the electron beam rapidly returned
again to the left of the screen to start again sweeping the next
horizontal line. Pulses that control the electron beam to return quickly
to the left of the screen is called "horizontal retrace pulses" and are
used to generate high voltage by installing tranfo on the horizontal
output. Therefore tranfo called flyback (another term is FBT flyback
transformer or HVT high voltage transformer). In other words as a
flyback high voltage generators are only ride along with the horizontal
deflection circuit.
Modern TV horizontal deflection circuit consists of :
- VCO (Voltage Controlled Oscillator)
- Horizontal Count-down (horizontal frequency dividers)
- PH1 or AFC1
- PH2 or AFC2
- Horizontal Driver
- Horizontal Output
- Horizontal deflection coils ( Def Yoke)
VCO, Horizontal Count-down, PH1 and PH2 circuit in modern TVs are in one packed intregrated circuit called IC Jungle.
1.02
VCO (Voltage Controlled Oscillator) is a high frequency oscillator
generator in which the frequency can be controlled by a voltage.
Various kinds of IC Junge has a slightly different working systems on
the VCO. On TV old model oscillator frequency is obtained by using
external ceramic resonator which has a frequency of 500Khz or RC
circuits (Resistor-Capacitor). On newer models the external resonator of
this kind have not been used again and use the reference oscillator
frequency of the oscillator that is also used for the processing of
color signal.
1.03
Generated VCO frequency is still very high and by the Horizontal Count
down will be lowered with divided manner in order to obtain horizontal
line frequency. The amount of horizontal frequency output will
automatically synchronise to the video signal received by the system.
If you receive PAL system is 15.625 Hz and if the received NTSC system
is 15.750 Hz.
1.06
Horizontal driver circuit serves to reinforce the horizontal frequency
signal from the IC Jungle before fed into the HOT. As the coupling an
tranfo generally used as a matching impedance of horizontal driver with
horisontal output, in order to obtain maximum coupling efficiency.
1.04 Europe generally use the term PH1 (Phase
Horizontal ) and the Japanese use the term AFC1 (Automatic Frekwency
Control). This makes circuit adjusts the frequency horizontal
automatically follow the received video signal and to stabilize the
"frequency". IF the horizontal frequency is not stable or changing
frequency will cause the image appears torn apart or collapse.
This circuit work by comparing the VCO horizontal frequency signal with
the horizontal synchronization frequency signals. If the two are not
equal, then the VCO frequency will be corrected by PH1 (AFC1) thus the
output frequency becomes equal to frequency of horizontal
synchronization signal.
1.05 PH2 (AFC2) functioned is to stabilize "phase" of
the horizontal frequency. Horizontal phase shifting will lead to
unstable images that appear "shifted toward to the left or right" of the
screen.
This circuit work by comparing the output frequency of the horizontal
phase with the phase of flyback pulse (FBP), which comes from pin-AFC
tranfo flyback. If both pulses are not the same, it will be corrected by
the PH2 (AFC2) to become stable. Horizontal-Shift ajusment circuits
associated with this section
The role of horizontal driver quite critical, because
- Ideally,
when the HOT become “on” state the resistance between the collector
with the emitter is zero. If you drive less will cause the HOT is not
fully "on", but still has a resistance that can cause HOT hot.
- Conversely
if the drive is over will cause the "storage time" or time needed to
return from the “on” state condition to “off” state of the HOT becomes
longer. As a result the period of "on time" HOT become longer, so the
transistor can also produce more heat.
1.07 Horizontal-output section is the most difficult
to understand. Form of voltage and current through each component differ
from each other. But in broad outline can be explained the function of
each part are as follows :
1.07.1 HOT (Horizontal Output Transistor) serves to
provide sufficient power to be able to generate voltage pulses to
horizontal deflection. HOT transistor generally get suply voltage B+ of
about 100 to 150v dc.
HOT transistor is not valid as an amplifier, but accepted as a "on-off
switch" pulses driven. At the period "on" state the collector-emitter
will be connected entirely where ideally the resistance is "zero". But
because the resistance of this ideal is not possible, then the
collector-emitter still has a small resistance which causes the
transistor to heat, so the HOT transistor needs to be installed on the
cooler.
Pulse current flows through the flyback transformer, resulting in a high
induction voltage approximately 1200v. This voltage stress will be
received by the collector-emitter HOT, therefore HOT must have a minimum
of working voltage 1500v.
1.07.2 Capacitor resonat. Named because this capacitor
form a parallel resonance circuit together with the coil of flyback and
def yoke. Other name is retrace timing capacitors, safety capacitors,
snubber capacitors generally have a working voltage of 1600v and mounted
on the HOT collector to the ground.
Capacitor value is quite critical because they have the influence to the
duration period of "on" transistor HOT, raster width geometric and the
resulting of high voltage from flyback
- If the value of this capacitor decreases, change will cause
narrower left-right raster and all the flyback output voltage rise. It
will cause the induced voltage on the collector up for a few times so it
can damage the transistor HOT. In certain cases, this increased stress
which may damage the picture tube. TV has the X-ray protector circuit
will switch off automatically if the high voltage flyback rose
abnormally, thus preventing the occurrence of damage to the transistor
or the picture tube.
- If the value of resonant capacitor is replaced with a larger value,
consequences of high voltage will drop and the raster will be widened
horizontally.
1.07.3 Internally there is a diode in the HOT, so
called “Damper Diode” mounted between the collector-emitter. Without
damper diode due to the circuit of flyback tranfo there will be
oscillation that produces the voltage back and forth where the voltage
will be received by the collector-emitter HOT. If no damper diode HOT
sometimes will get the voltage with reverse polarity. Of course this
will cause the transistor is damaged.
Damper diode serves to dampen the oscillation. At emitter get the
voltage (+) and the collector (-), the current will flow throuh diode
damper. On TV old model using the HOT without internal damper diode and
an additional damper is installed outside of the transistor.
1.07.4 Because of the characteristics def yoke coils
that are not purely inductive, but also has a resistive characteristic,
then this caused the so-called " horizontal linear flaw." Flaw cause the
image on the right side of the screen is compressed, so if screen
display the image of an announcer their right and left shoulder will be
appeard to be asymmetrical. These flaw will appear more clearly if the
image display pictures of “cross hatch” patern generator. A coil is
called Horizontal Linear (H Lin) is installed in series with the def
yoke serves to fix this flaw. Installation of coil polarity must not be
reversed, and to avoid errors in installation, the body coil and the
circuit board are generally given a certain mark.
1.07.5 Due to the dimensions of the picture tube
screen, the distance from the electron gun towards the screen is
uneven. This causes the defect called "S flaw". This is because the
horizontal sweeping velocity of electrons on the left and the right of
the screen is relatively faster than that during the middle of the
screen. This causes the image to the left and the right of the screen a
little wider than the middle. In contrast to the horizontal linear flaw
that affect only one side, then the "S flaw" influence on both the left
and right side of the screen. These defects appear to be more clear if
the display pictures of “cross hatch” patern generator.
A capacitor called "S" is used to correct these flaws and generally have
a working voltage of 200v. This capacitor value is fairly critical,
therefore if replaced should be used with the same value.
- If the capacitor value is changed smaller it will lead image of
the of the left and right of the screen will be like being compressed.
- Meanwhile, if the capacitor value larger then will cause the image
of the left and right of the screen will be like being stretched.
1.07.6
A called “cross-hatch flaw” only apparent if the image displays images
of cross-hatch patern, will be visible lines twisted like a worm on each
vertical-horizontal crossing. In horizontal out circuit mounted a
circuit called "kink correction" to eliminate this flaw. Circuit
consists of a diode, a small high voltage electrolytic capsitor 160v and
a resistor that is placed in parallel with the capacitor "S". Damage to
one part of this circuit will not appear show or interfere image if a
TV receives regular image.
1.07.7 Horizontal def yoke coil mounted on the neck of
the picture tube is used to control the electron beam to make sweeping
horizontally from the left to the right of the screen. Horizontal
deflection coil has a pair of coils mounted on top and bottom of the
picture tube neck which is generally connected in parallel.
2. Generating anode flyback high voltage
2.01
Current used to control the horizontal sweeping so that the electron
beam sweeps a horizontal line image from the left of the screen to the
right. Then, with a high speed current will return the electron beam
goto the left of the screen to start repeating again next. This
generates pulse sweep so called "horizontal retrace pulse." These pulses
are used to generate a anode high voltage by placing a tannfo.
Therefore this tranfo called flyback.
Retrace horizontal currents that change very quickly in the primary will
induce a secondary high voltage at about 20 to 30Kv and rectified
using a high voltage diode rectifier.
VR or potensio as high voltage divider is installed inside the body in
order to obtain high-voltage for focus voltage around 6Kv and for screen
voltage around 500V.
Except that the flyback is also used to generate low voltages such as for the vertical-out, heater and video drives.
Sony TVs that use Trinitron tubes require a screen voltage of about 400 ~
800v. Screen voltage is not obtained from tranfo flyback, but obtained
by rectify horizontal pulses by placing a diode in the collector of HOT.
In
a simple TV to correct the defect breathing normally mounted a power
resistor on the B+ supply line . If contrast or image britnes rise
consequently increases the flow of B+ current and lead to voltage drops
across the resistor getting bigger (voltage drops V = I x R). As a
result, the output voltage suply to the horizontal drops and the
horizontal deflection also drops so that the raster is not so swell. Big
screen TV is usually wearing breathing circuit using an EHT input pin
found on the IC Jungle. Flyback pulse from pin-connected to the EHT and
connected with the correction that will automatic control EW Horizontal
and Vertical-size.
2.02 High Voltage diode rectified using a serial row
of diodes, thus resulting in having a relatively high internal
resistance. Small current changes can cause high voltage drops. If high
voltage drops will cause the electron beam velocity is decreased and
more easily bent by def yoke, so that the result would expand raster
horizontal and vertical (blooming).
The contrast or changing image britnes changes high voltage current, so can makes raster pulsate (breathing).
2.03
The horizontal pulse frequency is about 15 Khz. The advantage with the
use of high frequency to generate high voltages is that the number of
windings of tranfo to raise the required voltage is relatively not much
if compared to using conventional tranfo used in ac mains frequency
50Hz. If to generate high voltage using a transformer as used on power
supply, will certainly require more rolls, more space, and more weight.
Because working at high frequencies, the core of the flyback tranfo use
of ferrite materials
2.04 Pulses from the flyback circuit is given to the other circuit with functions for :
- Pulse
given to the microcontroller as Hor Sync pulse, which together Vert Sync
pulse of the vertical pulses used for the purposes of generating OSD
character (On Screen Display). If the pulse is interrupted, it will
cause the OSD is not displayed.
- Pulses
applied to the ic Jungell / Video Chroma serves to blangking pulse,
sand-castle signal generator, color processor and a pulse for PH2
(AFC2). If the pulse is interrupted can cause dark raster, the image is
slightly shifted so that there appears a black block on the right side
of the screen.
- On some TV
models from the flyback pulse is used for synchronization to the SMPS
(Switch Mode Power Supply). Serves to eliminate interference to the
image frequency SMPS. If this pulse disconnected can cause problems such
as, whittling power supply, power supply does not work, flaw of a back
ground image disorders such like as wood fiber.
3. Understanding how the EW correction circuit (Pin Cushion)
In the
big-screen TV or flat screen, the problem is that line curved flaws on
either side of the screen so that the raster image is shaped like a
pillow. Other terms are "pin-cushion" or "EW". This is due to geometry
differences are not uniform distance between the electron gun element to
the whole surface of the screen. Corners of the screen have the most
far distance compared with the middle of the screen. As a result, the
horizontal deflection at the corners of the screen is wider than in the
middle of the screen. Pin-Cushion flaws were corrected using correction
circuit called EW or Pin Cushion.
EW correction circuit comprises :
- Circuit-forming
"vertical-parabola pulses ", ie circuits that generate parabolic shape
pulses with a vertical frequency. It gets the signal from the vertical
output circuit.
- Pin
Amplifier, is a power transistor which serves to strengthen the vertical
parabolic signals, used to driving "Split Diode Modulator."
- Split Diode
Modulator consists of two pieces diode mounted on HOT collector.
Vertical parabola voltage pulse is injected into this section that will
affect the suply voltage to the HOT collector that will control the
horizontal size of horizontal deflection.
On TV old model has two kinds of adjustments that are still using the VR geometry, namely
Old fashion
model a Pin or EW VR to regulate the size of the parabolic curve that
will affect the shape of curvature of the left-right in order to become
straight (EW). And an other VR to set the dc voltage of base of the
transistor pin-amplifier which will affect the width of the left-right
side of the screen (H size).
In the new TV models ajustment geometry is done through Service Mode using the remote control.
Here are some kind of geomatry adjustment. Ajustment should be conducted using cross-hatch patern generator.
- Pin amplifier - to adjust the curvature of the line on the left and right edges to be straight lines
- Size Hor - to set raster width of the left-right of thescreen
- Upper pins - to set the crooked line defects in the left-right upper corner of the screen
- Lower pin - to set the crooked line defect on the left-tight bottom corner of the screen
- Hor Shift - to set the center the image horizontally
- Trapezoid or Tilt or - adjust the trapezoid-shaped defects raster in order to become a square.
- Hor Bow - to set the defect line in the middle of the screen is curved so that a straight line
- Hor Angel - to set straight-line defects are askew in the middle of the screen to be perpendicular.
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