Philips 286NS-05, Руководство по обслуживанию

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9 CIRCUIT DESCRIPTION
25 Comet
mains. The optocoupler is driven by pin 37 of IC7100-6E via
transistor TS7103. When TS7103 is not conducting,(the LED of
the optocoupler is also out of conduction) TS7421 is also not
conducting. In this way TS7422 will conduct and the 96V is
placed over winding 2-1 of the LOT. A voltage over winding 2-
1 of the LOT will cause a voltage over the windings 8-10, 6-10
and 9-10. Now energy will be transformed from the primary to
the secondary-side and charge capacitors C2424 and C2425.
C2430 will be charged to the difference of the +40D and +14D
(=26V) when TS7422 is conducting. When TS7422 stops
conducting, the voltage of pin 8 of the LOT will become very
negative. This forces C2430 to be charged to 26V plus the
absolute value of pin 8. When TS7422 starts conducting again
the voltage of pin 8 of the LOT will increase and so the voltage
on the anode of D6422. In this way the 160V is created. This
means that during the off-time of TS7422, C2430 is charged
and during the on-time of TS7422, the energy in C2430 is given
to C2426. When transistor TS7103 conducts, the LED of the
opto-coupler will be activated. This causes the transistor of the
opto-coupler to conduct, which drives TS7421 in conduction.
This brings TS7422 out of conduction. Due to this construction,
this circuit is protected against missing line-drive pulses. When
a line-drive pulse is missed, the line-transistor stays out of
conduction, due to the fact that the diode of the opto-coupler is
forced into conduction by TS7103. In this way nothing can be
damaged when there is no line-drive.
Winding 4-3 is an extra winding to help TS7422 to switch.
On the secondary-side of the LOT there is a circuit consisting
of TS7423, R3422, R3433, R3434, C2431 and C2432. This
circuit creates a pulse when TS7422 switches off. This pulse
indicates that horizontal flyback takes place. This information is
fed to IC7100-6E to blank the picture.
9.5 Stand-by:
The standby signal from the mC is low in case of stand-by. Now
TS7103 is brought into conduction by R3100. As mentioned
before this will switch off the line-output stage completely.
9.6 Deflection :
9.6.1 Horizontal deflection:
The voltage over capacitor C2422 is the same as the voltage
over C2515 (96V). When TS7422 is conducting this voltage is
placed over the horizontal deflection coil. This causes a linear
increasing current through this coil. In this way deflection is
created. When TS7422 switches of flyback takes place and it
starts all over again. L5424 is used for linearity correction.
9.6.2 Vertical deflection:
Vertical deflection is based on a balance amplifier. Or TS7401
or TS7402 is conducting. This depends on the signal V-drive. If
V-drive is high TS7401 conducts and the voltage of C2401 is
placed over the deflection coil. Now the picture is written. When
V-drive is low, TS7402 conducts and the +40V supply voltage
minus the voltage over C2401 is placed over the deflection coil.
Flyback takes now place. In this way deflection is generated.
R3407 is used to adjust the vertical shift. With this resistor the
level of the signal VFB is adjusted. R3402 and C2404 are used
to damp oscillation of the deflection coil with his parasitic
capacitance. The signal NIL from the mC is used to create a
non-interlaced mode. This is done by creating a small DC
current through the deflection coil.
9.7 110 degrees deflection module
For the 25" and 28" sets a 110 degrees module is needed for
East/West correction. This panel is allocated on the right hand
side of the mainboard (seen from the rear). East/west
correction in this module is based on the diode-modulator
principle; the current through the horizontal deflection coil is
modulated. As this is done by a parabolic-shaped voltage, E/W
distortion is corrected. This parabolic-shaped voltage is
derived from a saw-tooth-shaped voltage of the frame
deflection.
9.7.1 Frame (time base frame)
Because the raster part is fed by the primary side a galvanic
isolator must be applied between IC 7100 (= so called Bimos
ic) in the secondary side and the raster amplifier on primary
side. This is realised by opto coupler (7422); this opto coupler
will be switched and it will block the saw-tooth of the Bimos ic.
So we don't use the saw-tooth of the Bimos((pin 42) or the
feedback frame input(pin 41). The only information from the
Bimos ic (=IC7100) is the flyback command(pin 43). The output
of this pin is a pulse of 6 to 0 Volts during 1 mS with a period of
20mS. This signal blocks transistor 7424 and this causes
conduction of the opto coupler diode (7422). The internal
transistor also conduct and pins 11 and 12 (connector 00820)
of the 110 module will be short circuited.
9.7.2 Raster part
A saw-tooth must be created because we don't use it from the
Bimos ic(see annex 5). Via 150V C2901 will be charged via
R3901, R3900 and D6900; the function of D6901 is to
determine the lower part of the potential level. After 20mS a
signal coming from the Bimos ic will short-circuit pins 11 and 12
of connector 0082 and C2901 will be discharged. It is a must to
have an amplitude on the screen independent of the 50Hz or
60Hz frequency of the mains; see circuit diagram annex 6. The
emitter voltage of T7900 can be adjusted with potentiometer
3903; this is the top Voltage of the saw-tooth. This is the circuit
for adjusting the vertical amplitude independent of the 50/60Hz
frequency. The saw-tooth will control T7901 and this transistor
controls the amplifier (= T7902, T7903 and T7904).D6902,
D6903, T7905 and C2904 determines the flyback. This flyback
pulse is negative and is created by an inverted polarity of
C2904.During the deflection T7905 is blocked and C2904
charges; during the flyback T7905 conducts and the flyback
pulse will be made.
9.7.3 East-West modulator
The parabola is taken on C2907; R3916 and D6905
determines the shape of the parabola and they corrects the
upper and lower parts. The parabola is fed via C2908 to
potentiometer 3913; this for adjusting the pin-cushion
correction. Via T7904 this signal goes to MosFet 7908; the Vgs
command has two functions by changing the Voltage of Vgs by
potentiometer 3924: pin-cushion correction and horizontal
amplitude adjustment.
Special components:
• D6904 + R3916: temperature compensation of Vbe
(T7904)
• R3935: trapezium correction
• C2909: to avoid external radiation
• C2918: to avoid "twisted or broken" lines