Circuit Description
9.
divided by two, to lock the first control loop to the incoming
signal.
When the IC is switched ‘on’, the ‘Hdrive’ signal is suppressed
until the frequency is correct.
The ‘Hdrive’ signal is available at pin 30. The ‘Hflybk’ signal is
fed to pin 31 to phase lock the horizontal oscillator, so that
TS7462 cannot switch ‘on’ during the flyback time.
The ‘EWdrive’ signal for the E/W circuit (if present) is available
on pin 15, where it drives transistor 7400 to make linearity
corrections in the horizontal drive.
When the set is switched on, the ‘+8V’ voltage goes to pin 9 of
IC7200. The horizontal drive starts up in a soft start mode. It
starts with a very short T
ON
time of the horizontal output
transistor. The T
OFF
of the transistor is identical to the time in
normal operation. The starting frequency during switch on is
therefore about 2 times higher than the normal value. The ‘on’
time is slowly increased to the nominal value in 1175 ms. When
the nominal value is reached, the PLL is closed in such a way
that only very small phase corrections are necessary.
The ‘EHTinformation’ line on pin 11 is intended to be used as a
‘X-ray’ protection. When this protection is activated (when the
voltage exceeds 6 V), the horizontal drive (pin 30) is switched
'off' immediately. If the ‘H-drive’ is stopped, pin 11 will become
low again. Now the horizontal drive is again switched on via the
slow start procedure.
The ‘EHTinformation’ line (Aquadag) is also fed back to the
UOC IC7200 pin 54, to adjust the picture level in order to
compensate for changes in the beam current.
The filament voltage is monitored for ‘no’ or ‘excessive’ voltage.
This voltage is rectified by diode 6447 and fed to the emitter of
transistor TS7443. If this voltage goes above 6.8 V, TS7443 will
conduct, making the ‘EHT0’ line ‘high’. This will immediately
switch off the horizontal drive (pin 30) via the slow stop
procedure.
The horizontal drive signal exits IC7200 at pin 30 and goes to
TS7462, the horizontal driver transistor. The signal is amplified
and coupled to the base circuit of TS7460, the horizontal output
transistor. This will drive the line output transformer (LOT) and
associated circuit. The LOT provides the extra high voltage
(EHT), the VG2 voltage and the focus and filament voltages for
the CRT, while the line output circuit drives the horizontal
deflection coil.
9.5.2
Vertical Drive
A divider circuit performs the vertical synchronisation. The
vertical ramp generator needs an external resistor (R3245, pin
20) and capacitor (C2244, pin 21). A differential output is
available at pins 16 and 17, which are DC-coupled with the
vertical output stage.
During the insertion of RGB signals, the maximum vertical
frequency is increased to 72 Hz so that the circuit can also
synchronise on signals with a higher vertical frequency like
VGA.
To avoid damage of the picture tube when the vertical
deflection fails, the guard output is fed to the beam current
limiting input. When a failure is detected, the RGB-outputs are
blanked. When no vertical deflection output stage is connected,
this guard circuit will also blank the output signals.
These ‘’ and ‘V_DRIVE-‘ signals are applied to the
input pins 1 and 2 of IC7471 (full bridge vertical deflection
amplifier). These are voltage driven differential inputs. As the
driver device (IC7200) delivers output currents, R3474 and
R3475 convert them to voltage. The differential input voltage is
compared with the voltage across measuring resistor R3471
that provides internal feedback information. The voltage across
this measuring resistor is proportional to the output current,
which is available at pins 4 and 7 where they drive the vertical
deflection coil (connector 0222) in phase opposition.
IC7471 is supplied by +13 V. The vertical flyback voltage is
determined by an external supply voltage at pin 6
(50V). This voltage is almost totally available as
flyback voltage across the coil, this being possible due to the
absence of a coupling capacitor (which is not necessary, due
to the ‘bridge’ configuration).
9.5.3
Deflection Corrections
The Linearity Correction
A constant voltage on the horizontal deflection coil should
result in a sawtooth current. This however is not the case as the
resistance of the coil is not negligible. In order to compensate
for this resistance, a pre-magnetised coil L5457 is used. R3485
and C2459 ensure that L5457 does not excite, because of its
own parasite capacitance. This L5457 is called the 'linearity
coil'.
The Mannheim Effect
When clear white lines are displayed, the high-voltage circuit is
heavily loaded. During the first half of the flyback, the high
voltage capacitors are considerable charged. At that point in
time, the deflection coil excites through C2465. This current
peak, through the high-voltage capacitor, distorts the flyback
pulse. This causes synchronisation errors, causing an
oscillation under the white line.
During t3 - t5, C2490//2458 is charged via R3459. At the
moment of the flyback, C2490//2458 is subjected to the
negative voltage pulses of the parabola as a result of which
D6465 and D6466 are conducting and C2490//2458 is
switched in parallel with C2456//2457. This is the moment the
high-voltage diodes are conducting. Now extra energy is
available for excitation through C2465 and the line deflection.
As a consequence, the flyback pulse is less distorted.
The S-Correction
Since the sides of the picture are further away from the point of
deflection than from the centre, a linear sawtooth current would
result in a non-linear image being scanned (the centre would
be scanned slower than the sides). For the centre-horizontal
line, the difference in relation of the distances is larger then
those for the top and bottom lines. An S-shaped current will
have to be superimposed onto the sawtooth current. This
correction is called finger-length correction or S-correction.
C2456//2457 is relatively small, as a result of which the
sawtooth current will generate a parabolic voltage with
negative voltage peaks. Left and right, the voltage across the
deflection coil decreases, and the deflection will slow down; in
the centre, the voltage increases and deflection is faster. The
larger the picture width, the higher the deflection current
through C2456//2457. The current also results in a parabolic
voltage across C2484//2469, resulting in the finger length
correction proportionally increasing with the picture width. The
east/west drive signal will ensure the largest picture width in the
centre of the frame. Here the largest correction is applied.
East/West Correction
In the L01, there are three types of CRTs, namely the 100º,
110º and wide screen CRTs. The 100º CRT is raster-
correction-free and does not need East/West correction.
The 110º 4:3 CRT comes with East/West correction and East/
West protection.
The wide screen TV sets have all the correction of the 110 4:3
CRT and also have additional picture format like the 4:3 format,
16:9, 14:9, 16:9 zoom, subtitle zoom and the Super-Wide
picture format
A line, written at the upper- or lower side of the screen, will be
larger at the screen centre when a fixed deflection current is
used. Therefore, the amplitude of the deflection current must
be increased when the spot approaches the centre of the
screen. This is called the East/West or pincushion correction.
Summary of Contents for L01H.1A
Page 5: ...Directions for Use EN 5 L01H 1A 3 3 Directions for Use ...
Page 7: ...Directions for Use EN 7 L01H 1A 3 ...
Page 8: ...Directions for Use EN 8 L01H 1A 3 ...
Page 9: ...Directions for Use EN 9 L01H 1A 3 ...
Page 10: ...Directions for Use EN 10 L01H 1A 3 ...
Page 11: ...Directions for Use EN 11 L01H 1A 3 ...
Page 12: ...Directions for Use EN 12 L01H 1A 3 Personal Notes ...
