Hitachi 51F510, Manual

Page: 56 / 152

DP-4X ABL CIRCUIT EXPLANATION
PAGE 03-10
(See ABL Circuit Diagram on the next page for details)
The ABL voltage is generated from the Flyback transformer TH01 ABL pin ( 8 ). The ABL pull-up resistors are
RH27 and RH28 . They receive their pull up voltage from the SW +115V which is the B+ line for Deflection cre-
ated in the Power Supply.
ABL VOLTAGE OPERATION
The ABL voltage is determined by the current draw through the Flyback transformer. As the picture brightness
becomes brighter or increases, the demand for replacement of the High Voltage being consumed is greater. In
this case, the Flyback will work harder and the current through the Flyback increases. This in turn will decrease
the ABL voltage. The ABL voltage is inversely proportionate to screen brightness.
Also connected to the ABL voltage line is
DH16 . This zener diode acts as a clamp for the ABL voltage. If the
ABL voltage tries to increase above 10V due to a dark scene which decreases the current demand on the flyback,
the ABL voltage will rise to the point that
DH16 dumps the excess voltage into the 10V line.
ACCL TRANSISTOR OPERATION
The ABL voltage is routed through the PDS2 connector pin 3 to the Signal PWB. Then the ABL voltage is
routed through the acceleration circuit RY32 and DY01 to the base of QY09 . Under normal conditions, this tran-
sistor is nearly saturated. QY09 determines the voltage being supplied to the cathode of DY02 , which is con-
nected to pin
78
of the Rainforest IC,
IY04
. During an ABL voltage decrease due to an excessive bright circum-
stance, the base of QY09 will go down, this will drop the emitter voltage which in turn drops the cathode voltage
of DY02 . This in turn will pull voltage away from pin 78 of the Rainforest IC, IY04 . Internally, this reduces the
brightness, contrast and color gain voltage which is being controlled by the
I
2
C
bus data communication from the
Microprocessor arriving at pins 29 and 30 of the Rainforest IC and reduces the overall brightness, preventing
blooming as well as reducing the Color saturation level to prevent color smear.
ABL SWITCH QH03
This chassis has the ability to change the Side Panels when watching a NTSC 4X3 image. When a 4X3 images is
displayed on a 16X9 set, the sides do not reach the edges. To avoid excessive ageing at the 4X3 display area, the
side panels IRE levels are raised. However, sometimes the customer may want to turn the side gray panels off.
Through the Video Advanced features Menu the customer can do this. When the Side panels are turned off, the
overall average ABL level for the image is reduced. To compensate,
QH03 ABL Switch is turned on. The Micro-
processor I004 tells the Sub Deflection IC IB01 via I
2
C communication to output a high from the DAC2 line pin
2
. This high is routed through the
PPD1
connector pin
11
, to the base of
QH03
turning it
On
. This adds Resis-
tor RH29 to the ABL pull up circuit and the ABL level drops slightly to compensate for the loss of brightness
when the side panels go black.
RH32
manipulates the trigger point of shut down dependant upon the ABL level avoiding false triggering.
NOTE: For the Circuit connected to the Xray Protect line, see the Deflection Side Shutdown Circuit Diagram for details on
Page 01-05.
Gray Side Panels
Black Side Panels
Black Side Panels
Turned on by the
customer