– 38 –
AUTOMATIC BRIGHT LEVEL ADJUSTMENT SYSTEM (Continued)
When the command data for the Automatic Bright Level Adjustment is input
from the remote control, the CPU starts the automatic adjustment program.
Automatic Bright Level Adjustment Program
First, the Time Base signal at pin 26 of the CPU is checked. When the video
signal is input to the TV, the Time Base signal at pin 26 is High. If the Time
Base signal can not be confirmed, the CPU executes an error process to
cease the automatic adjustment operation.
After confirmation of the Time Base signal, the CPU presets the BUS data
outputs of the picture controls to eliminate beam current. The controls are set
as follows: BRIGHTNESS 0/27 (= 0/63 for Bright Level Adju 0/64 for
Customer Control), CONTRAST 0/64, COLOR 0/64*, TINT 32/64 and
SHARPNESS 32/64.
* ....The Color Killer enabling BUS data is automatically input to the BUS
Interface circuit within IC101 to write a 1 bit data “1” into the Color Killer
Control Register, minimizing the output of the color control during the
Automatic Bright Level Adjustment.
With a low amplitude, flat video signal (12 IRE) input to the TV and the +B
(130V) DC power applied to the flyback transformer and the beam current
detection circuit, no beam current is supplied to the CRT. Maximum current
is now input to the beam current detection circuit and maximum DC voltage is
input to pin 30 (A/D input) of the CPU.
When the maximum A/D input voltage at pin 30 is between 21/128 Vcc
(0.82V) and Vcc (5.0V), the specified video signal is determined to have been
input and the A/D input voltage is read by the 5 bit (31 steps) comparator.
The CPU will begin decreasing the reference voltage from 125/128 Vcc (31/31
steps) sown to 21/128 Vcc (5/31 steps) by 2steps (8/128 Vcc) until the
reference voltage becomes just lower than the A/D input voltage. The
reference voltage is now memorized as a standard voltage (A) and stored in
IC802, the Memory IC. If the A/D input voltage is lower than the 21/128 Vcc
(0.82V), the CPU executes an error process to cease the automatic
adjustment operation. See example of A/D Input Voltage on previous page.
After determination of the standard voltage (A), the CPU changes the BUS
data outputs of brightness and contrast controls for FACTORY PRESET mode
as follow: BRIGHTNESS 50/127 (= 0/63 for Bright Level Adju 50/64
for Customer Control), CONTRAST 64/64.
The CPU will now decrease the reference voltage of the comparator 5 steps
(20/128 Vcc) lower than the standard voltage (A) and compares it with the A/D
input voltage. When the A/D input voltage is higher than the reference
voltage, the CPU increases the BUS data output of the Bright Level
Adjustment from 0/63 up to 63/63 step by step until the A/D input voltage
becomes just lower than the reference voltage. The BUS data output step of
the Bright Level Adjustment is memorized into the Memory IC and the CPU
exits the automatic adjustment mode.
