Hv Circuit; Dynamic Focus Circuit Operation; Vm Circuit Operation - Hitachi 36SDX88B Service Manual

10.3 HV Circuit
High Voltage circuit for CRT anode voltage and regulation consist of IH02 (Control IC), drivers QHl4, QH15,
QHq6, and HV output QH02.
When the TV is switched on, IH02
HV drivers. IH02 also regulates the
picture brightness changes.
internal oscillator starts up to generate a pulse voltage as a source for the
HV to keep the picture size fixed by controlling the HV pulse width when the
IH02 oscillator time constant is dependent on RHI 9 and CH 10. H. blk pulses are appiied to pin (10) as a trigger
and to synchronize the oscillator.
A sawtooth voltage is generated and compared with to the voltage at pin (12) to produce a pulse voltage, which
is output at pin (7) to the HV drivers. QH16, QH14, AND QH15 amplifiers this pulse voltage to drive QH02 which
produces a HV pulse at QH02 0 to the FBT THO'l to provide Anode, focus and screen voltages.
10.4 Dynamic Focus Circuit Operation
The dynamic focus circuit improves the focus at the corners of the screen. This requires higher focusing voltage
due to the distance from the center. The focus voltage is varied in a parabolic form as the electron beam scans
horizontally and vertically.
The FBT pulse is integrated by LF02 and CF05 then amplified by QF05 and clamped by QF04(DF PWB).The
amplitude is increased by QF53, QF52 and QF55 provides temperature stability.
The vertical output pulse is integrated by RF19 and CFO9 (DF PWB) to produce a parabolic wave form. It is
amplified by QF58 and added to the Horiz. Parabola and applied to the Focus pin (DF) on FBT THOI.
1 I. VM Circuit Operation
The VM circuit improves the definition between black and white edges by accelerating or decelerating the
horizontal scanning speed of the electron beams. As a result, the gradient of the ramp of the leading edge of
the luminance signal is increased with the brightness changes and the video bandwidth of the video signal
narrowed simultaneously to sharpen the edged.
The Y signal is differentiated by Q552. The second differential of the Y signal is applied to Q556, VM amplifier,
then to the VM drivers, QL08 and QL09 are the VM output amplifiers which drive the VM coil the current applied
to the VM coil creates a magnetic field which varies the velocity of the horizontal scanning of the electron beam.
The Ys signal is applied to Q555 to cut-of the VM when OSD is displayed. Q552, Q555, and Q556 are sub VM
circuit. QL08 and QL09 are VM circuit.
TO VM COILS
Fig. 11.1 VM Block Diagram
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