(5-L -5) Parabola Waveform Generating Circuit - NEC MultiSync 4FGe Service Manual

5-1-5. Parabola Waveform Generating Circuit
The parabola-waveform generating circuit is mainly composed of two blocks (See Fig 5-1-l 0 and Fig 5-l-11)1
Each block includes a multiplier which has two input terminal. In the first block, a parabolic waveform is
generated from the saw tooth wave. The saw tooth wave is generated at pin @ of IC4Al and is A C coupled
by C4CO to each terminals of IC4A2.
The multiplier of IC4A2 squares the A C coupled saw tooth waveform and produces a parabolic waveform.
Trapezoid distortion is corrected by the voltage applied to pin @I of IC4A2 through R4A2. This voltage is
determined by the vertical size and varied by VR404. The amplitude of the parabola waveform has to be
proportional to the +8 voltage of H deflection. In the
the parabola waveform and the amplitude is user control adjustable. +B voltage of H deflection is divided by
R409 and VR403.
The parabola wave and the H deflection +B are applied to each terminals of IC4A3 the user control adds to
subtracts from the divided +B H deflection voltage. The positive or negative user control voltage is obtained
transforming the control voltage from the microprocessor. The +B H deflection voltage varies as the H
frequency varies the necessary range of control voltage is also proportional to the +B H deflection voltage. So
in order to keep the variable quantity of the side pin cushion correction not so different at any frequency, the
range of control voltage is different for each four bands of horizontal frequency.
With using above method, the last parabolic wave is output from pin @ of IC4A3.
FIRST BLOCK (PARABOLIC WAVEFORM GENERATION DETERMINED BY V SIZE)
V CONTROL
BLCK
SECONDBLOCK PARABOLIC WAVEFORM AMPLITUDE GENERATION PROPORTIONAL TO
(Fig 5-l-10) The BLOCK DIAGRAM of PARABOLA waveform generating circuit
SUBTRACTION CONTRAST
CIRCUIT
64
second
block, the transaction of making the amplitude of
,
SAW TOOTH A C
MULTIPLIER 1