Sony KP 48S70, Training Manual

Page: 71 / 101

xxix
Circuit Description
The sensor amplifier is responsible for taking the amount of light received
by the sensors and outputting a DC value to the PJED CPU to represent
the amount of light received. The optimal value achieved is memorized
during the Auto Focus function in the Service Mode.
As the patterns of flashing light are seen on the screen, the outputs of the
sensors are input to the A board at CN524, CN525 and CN501. These
sensors are applied to IC1601 and IC1604. These ICs are current to
voltage converters. They are required because the sensors output a cur-
rent proportional to the amount of light they receive.
The outputs from IC1601 and IC1604 are output to peak hold circuits.
These circuits consist of IC1605 and IC1606 and buffer transistors Q1609
through Q1616. To ensure precise measurements, each sensor also has
its own reset line that grounds the peak hold circuit every vertical blanking
pulse. The top, left, right and bottom sensors’ outputs are applied directly
to the BD board. The four corner sensors are applied to a switch. The
switch is necessary because the PJED CPU only has six A/D inputs. Since
we do not need to use the corner left and right sensors at the same time,
they are switched. Pulses from CN1701/12 from the BD board are re-
sponsible for switching the sensors. The two sensors selected then have
their outputs applied to the PJED CPU.
5
3
0
2
7
4
1
6
SCREEN
0 : UPPER SENSOR
1 : LEFT SENSOR
2 : RIGHT SENSOR
3 : LOWER SENSOR
4 : UL SENSOR
5 : UR SENSOR
6 : LL SENSOR
7 : LR SENSOR
The picture above shows the sensor locations by number. The following
are the formulas used to perform the centering and skew adjustments.
V Center = 1+2
V Skew = 1-2
H Center = 0+3+(1+2)/2
H Skew = 0-3+(4+5-6-7)/4