Panasonic EURO 4 Chassis, Technical Manual

Page: 100 / 163

3DQDVRQLF
17
Chapter 2 EURO 4 Supplement
2.3.1. RGB 4:3 Mode
On those models which use the VDP IC601 located
on the E-Board, an additional circuit is required. This
additional circuit is used to support the display of RGB
in 4:3 mode.
Where a normal composite or S-VHS signal is
processed and displayed on screen, horizontal
compression and expansion takes place in the
horizontal scaler stage within the VDP. However the
RGB signal which is also fed to and processed by the
VDP is inserted after the VDP’s horizontal scaler
stage, meaning that no horizontal compression can
take place. To over come this problem, located on the
P-Board (page 14) is, a relay RL580.
Where a normal wide screen display is processed the
the horizontal drive signal is fed from the line output
transistor Q551, via connector E4 to the P-Board and
connector P4. Here the horizontal drive signal is
output to the horizontal scan coil connected to
connector P3 pin 4 and fedback to the P-Board via
connector P3 pin 1. The horizontal signal is then fed
via an L/C/R circuit made up of coil L580, resistor
R580 and capacitor C580, from here the signal is fed
via the relay contact of RL580, controlled by transistor
Q580 and pin 45 of the microprocessor IC1101.
In normal wide screen display transistor Q580 is
biased into conduction, via a pull-up resistor R1180
(located on the E-Board). This results in current flow
being fed via R589 (connected to the 15V supply line),
the relay winding and the collector-emitter junction of
transistor Q580. This current flow via the relay
winding of RL580 results in the switch closing, short
circuiting coil L585 and resistors R584 and R585. The
horizontal signal is then finally fed via coils L581, L584
and L582 back to the E-Board and the FlyBack
Transformer (FBT) T551.
However when an RGB signal is input and displayed
in 4:3 format the relay contact of RL580 is opened.
This is achieved again under the control of transistor
Q580 and pin 45 of the microprocessor IC1101, which
pulls the base of Q580 LOW. This results in the
transistor switching OFF and the relay contact
opening. When the contact of relay RL580 is open, the
path the horizontal signal follows changes. This sees
the horizontal signal being fed from the horizontal
scan coil back to connector P3 pin 1 (as mentioned
earlier) and fed via capacitor C586, the relay contact
and coil L585. The relay contact short circuiting L580,
R580 and C580. The horizontal signal is again finally
fed via coils L581, L584 and L582 back to the E-Board
and the FBT.
During these periods of 4:3 display the 150V supply
voltage to the DAF circuit is also reduced. This is
achieved by the circuit 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 R1180 (located on the E-board)
mentioned earlier, this HIGH level being fed via
connectors E9, P9 pin 3.
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
150V 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 45 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 fed
from the 15V 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 2 section 2.