Panasonic EURO 4 Chassis, Technical Manual

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3DQDVRQLF
72
Chapter 4 EURO 4D Supplement
Where a normal wide screen display is processed the
the horizontal drive signal is fed from the line output
transistor Q551, to connector E4. Here the horizontal
drive signal is output to the horizontal scan coil
connected to connector E4 pin 4 and fedback via
connector E4 pin 1. The horizontal signal is then fed
via an L/C/R circuit made up of coil L590, resistor
R590 and capacitor C590, from here the signal is fed
via the relay contact of RL590, controlled by transistor
Q590 and pin 79 of the microprocessor IC1101.
In normal wide screen display transistor Q590 is
biased into conduction, via a pull-up resistor R1141
(located at pin 79 of IC1101). This results in current
flow being fed via R599 (connected to the 15V supply
line), the relay winding and the collector-emitter
junction of transistor Q590. This current flow via the
relay winding of RL590 results in the switch closing,
short circuiting coil L595 and resistors R594 and
R595. The horizontal signal is then finally fed via coils
L595,
L591 and L594 back to the FlyBack
Transformer (FBT) T551.
However when an RGB signal is input and displayed
in 4:3 format the relay contact of RL590 is opened.
This is achieved again under the control of transistor
Q590 and pin 79 of the microprocessor IC1101, which
pulls the base of Q590 LOW. This results in the
transistor switching OFF and the relay contact
opening. When the contact of relay RL590 is open, the
path the horizontal signal follows changes. This sees
the horizontal signal being fed from the horizontal
scan coil (as mentioned earlier) via capacitor C596,
the relay contact and coil L595. The relay contact
short circuiting L590, R590 and C590. The horizontal
signal is again finally fed via coils L595, L591 and L594
back to the FBT.
During these periods of 4:3 display the 147V supply
voltage to the DAF circuit is also reduced. This is
achieved by the circuit (located on the W-Board)
consisting
of transistor Q3922, Q3923 and
opto-isolator D3922.
When a normal wide screen display is processed
transistor Q3922 is biased into conduction via a
pull-up resistor R1141 (located on the E-board)
mentioned earlier, this HIGH level being fed via
connectors E66, W6 pin 6.
When Q3922 is biased into conduction its collector
goes LOW removing any bias to the diode junction of
the opto-isolator D3922. With D3922 OFF transistor
Q3923 is also switched OFF. The supply voltage of
147V to the DAF circuit is thus fed via resistor R3901.
When an RGB 4:3 display is being processed the
base of transistor Q3922 is pulled LOW by pin 79 of
the microprocessor IC1101. With transistor Q3922
switched OFF the opto-isolator D3922 is biased into
conduction by a HIGH level fed via resistor R3902,
R3903 fed from the 12V supply line. This results in
transistor Q3923 also being biased into conduction by
a HIGH level fed via the collector-emitter junction of
D3922. With transistor Q3923 now conducting this
series regulator configured transistor reduces the
supply to the DAF circuit to approximately 90V. By
reducing the supply voltage to the DAF circuit the DAF
signal is also reduced, ensuring optimum picture
conditions as described in chapter 4 section 6.