Hitachi CL43WP910TAN, Service Manual

Page: 33 / 77

Two RGB sources are intended for use by the Digital Convergence Adjustment Signal, while the second is
used for the OSD and Teletext. The required
input signal has an amplitude of 0.5V Peak-to-Peak.
The switching between the internal signal and the OSD signal can be realized via a OSD BLK.
The circuit contains switchable matrix circuits for the colour difference signal so that the colour reproduction can
be adapted for PAL/SCAM and NTSC.
I2C is present at pins 27 & 28 (IX01) and +9V supply rails at pins 22, 40 & 46 and +5V supply rails at 12 pin.
CRT base
RGB signals for CRT are applied by PZC connector from RGB PCB to B CRT base PCB and bridged to G, R
CRT base PCB into Q8A1, Q851, and Q801. Then for e.g. B signal goes through limiter circuit Q8A2, Q8A3 to
amplifier Q8A4, Q8A5. B CRT base particularly has a gamma correction circuit, Q8A6 & Q8A7 which is
compensating B tube phosphorcharacteristic. Because B tube phosphor efficiency reduces in high brightness
area, therefore the B gain must be higher than others in high brightness area G CRT base has a bias circuit
Q858, Q859 for all CRT base PCB. Protection signal, which is called spot, is fed to CRT base to blank the picture
when something has failed.
Scan Velocity Modulation.
During transmission the signal sufferers from degradation and also due to the frequency characteristics of the television circuitry.
This normally results in a gentle rise or fall in the brightness change areas where black -to-white-to-black
patterns are received. The picture sharpness quality can be assessed by how steep the leading and trailing edges
are. The scan velocity modulation circuit has been designed to improve picture quality, ie make the video signal edges
steeper, by controlling the horizontal scanning velocity of the electron beam in the CRT. The velocity modulation
To
CRT PCB
Fig2. RGB Processor Block Diagram
RGB Processor
Y
U
V
IX01 TA1276AN
From
Feature Box
Clamp
Gen.
4:3 Frame
Gen.
2H Sync
Mask SW
IZ03
74HC221
IZ05
74HC221
Y
U
V
VM
Clamp
pulse