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through its emitter-base junction, R628 and C625, to ground. Q603 turns
ON increasing the voltage at error regulator IC602/pin 1. This results in
a decrease in T603 output to offset the no load condition at power OFF.
Reduce picture blooming
Picture blooming can occur when a bright scene is called for. This scene
causes the TV to draw the largest amount of power from the power sup-
ply at once. When the power supply is delivering the maximum amount
of current, it is functioning at the very top of the bell curve in the non-
linear region. At this operating point, the B+ regulation does not exist.
The picture may stretch disproportionately (blooming) as the B+ fluctu-
ates.
To avoid this, Q602 monitors the ABL voltage from the flyback trans-
former secondary. A bright scene causes this ABL voltage to decrease.
Q602 inverts this change and a positive going change is applied to the
error regulator IC602/pin 1. This results in a reduction of T603 output,
shifting the operating point away from the top of the bell curve. This
reestablishes regulation at very bright scene levels. Picture blooming as
a result of no regulation is reduced.
If Q602 failed, it would cause a negligible effect on the width of the pic-
ture. This can be understood by observing that there are only small
changes to the B+ voltage and converter frequency when Q602 is defec-
tive.
Results of Q602 Failure
Q602
Converter Frequency
Shorted c-e
68.8kHz
Normal
71kHz
Open c-e
72.5kHz
35
B+ Voltage
119Vdc
116Vdc
111Vdc
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