Dynamic Auto Focus (Daf) - Panasonic EURO 4 Chassis Technical Manual

3DQDVRQLF
Chapter 4
6. Dynamic Automatic Focus (D.A.F.)
6.1. Introduction
Euro 4D wide screen models have an additional circuit
provided, named Dynamic Automatic Focus (D.A.F.),
this circuit is used to overcome the problems of poor
focus at the outer edges of the picture which is
normally associated with large screen CRT's. By
using this D.A.F. circuit, focus of the picture at the
outer edges of the CRT are as sharp as the centre
portions of the picture.
To provide this feature an additional circuit located on
the W-Board is used (as shown on page 69). This
circuit containing IC3901 is discussed in the following
sections.
6.2. D.A.F. Processing
To carry out D.A.F. processing a horizontal and
vertical pulse are fed to IC3901.
The vertical pulse is output from the vertical output IC
IC451 pin 2 (LA7845) where the signal then splits into
two paths.
:
The first path feeds the vertical pulse to the
vertical deflection coil which is fed via connector
E4.
:
The second path feeds the vertical signal via the
zener diode D3931 and transistor Q3921 where
the signal is amplified and fed to connector E66
pin 5, here the vertical signal is passed to the
W-Board via connector W6. Once on the
W-Board the vertical signal is fed to IC3901 pin
15.
The horizontal pulse output from the horizontal output
transistor Q551 is split into four paths.
:
The first path feeds the horizontal pulse directly
to pin 10 of the flyback transformer T551
:
The second path feeds the horizontal pulse
directly to the horizontal deflection coil via
connector E4.
:
The third path feds a horizontal flyback pulse to
the video processing stage of the VDP IC601.
:
The fourth path feds the horizontal pulse to
connector E66 pin 4, where the horizontal pulse
is fed to the W-Board, and finally IC3901 pin 13
via amplifier transistor Q3901.
68
EURO 4D Supplement