Sony KP 48S70, Training Manual

Page: 65 / 101

xxiii
Convergence Block
Overview
The convergence circuits are used to adjust all three colors so that they
are all “laid on top of each other”. This is performed by sending signals to
sub deflection coils that are located on each of the three yokes. This is
done in the RA-4 chassis using Sony’s new digital convergence circuit.
To accomplish this, this circuit uses what is called the PJED (Projection
Engine Digital). The PJED performs two functions. It allows the factory
or servicer to converge the set, and also allows the customer to Auto
Focus the set. The Auto Focus button optimally adjusts the center and
skew controls.
Convergence
Convergence in this set is much different than in previous chassis. It is a
digital system that uses a coarse mode to “rough” in the picture, and then
a fine mode to allow 81 different points to be adjusted for each color
without affecting the rest of the picture. You will find this system to be
much simpler and intuitive than the previous system.
This system operates by allowing the servicer to interface with the PJED
using the remote. Remote commands are received by the Main CPU and
sent to the PJED over the main I²C bus. Once the CPU of the PJED
receives these commands, it sends data through its own I²C bus, referred
to as the P Bus, to an IC which outputs the correct waveforms. These
waveforms are output to the Sub Deflection amplifiers and applied to the
sub yokes.
Auto Focus (Auto Registration)
The Auto Focus button on the front of the set allows the customer to
adjust the skew and centering of the three colors at the touch of a button.
When Auto Focus is selected, the PJED OSD sends out signals, which
are sent through a level compensation circuit to the video processor to be
displayed on the screen. The patterns displayed on the screen are re-
ceived by a number of sensors located around the outside of the screen.
These sensors output a current proportional to the amount of light re-
ceived. The level compensation circuit was used earlier because the sen-
sors are not equally sensitive to different colors of light. The output from
the sensors is input to a current to voltage converter. The signal from the
I/V Converter is input to a peak detect circuit whose output is sent to an A/
D converter in the PJED. While this process is going on, the PJED is
changing the waveforms to the sub deflection circuit. This varies the
intensity of the light that strikes the sensors. The CPU will determine
when the output from the sensors equals the stored values of the opti-
mum picture. This means that it does not optimize the picture by itself,
but looks in memory for the stored value. This value is set at the factory
or by a servicer who presses the Auto Focus button in the service mode.