Panasonic EURO 4 Chassis, Technical Manual

Page: 96 / 163

3DQDVRQLF
13
Chapter 2 EURO 4 Supplement
2. Dynamic Automatic Focus (D.A.F.)
2.1. Introduction
Euro 4 wide screen models (PK1 and PK2) 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 P-Board (TNP8EP016) is used (as shown on page
14). This circuit containing IC3901 is discussed in the
following sections.
2.2. 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) or pin 3 (LA7876), and fed to
connector E4 to the P-Board via connector P4. Once
on the P-Board the signal splits into two paths.
:
The first path feeds the vertical pulse to the
vertical deflection coil which is fed via connector
P3.
:
The second path feeds the vertical signal via the
zener diode D3921 and transistor Q3917 where
the signal is amplified and 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 onto the P-Board via connector P4
to the horizontal deflection coil via connector P3.
:
The third path feds a horizontal flyback pulse to
the E-Board and to the video processing stage.
:
The fourth path finally feds the horizontal pulse
to IC3901 pin 13 via amplifier transistor Q3901.