X-Ray Protect - Hitachi 51SWX20B Training

DP-2X SIDE PINCUSHION CIRCUIT EXPLANATION
(See the DP-2X Side Pincushion Circuit for details)
Due to the nature of deflection, the sides of the picture has a tendencies to pull in similar to an hour glass. The
Side pincushion circuit is responsible for manipulating deflection to compensate. This is accomplished by super
imposing a vertical parabolic waveform on the DC voltage utilized for Horizontal Size.
VERTICAL YOKE CHARGE PULSE: (See Vertical Output Circuit for details)
The pulse generated on the positive side of C607 is routed through the parabolic wave form generation circuit of
R621, and C608 to the side pincushion circuit.
SIDE PIN WAVE FORM GENERATION IC:
Then through R742, C702, R709 to pin 6 of I701. This is the positive leg of the internal op-amp. Also attached
to this input circuit is the Horizontal Size circuit comprised of R710, R711, R713 and clamped by D714. The
variable resistor R711 which adjust the DC level at pin 6. The negative leg of the op-amp is connected through
pin 5 to the feedback circuit from the Side Pin Cushion output circuit for stability.
The output of the DC offset voltage with Vertical parabolic wave form attached is then routed out pin 7 to the
base of Q703. This transistor has it's emitter off set above ground by D713, R747 back to the SW +9V and
R704. This transistor drives the base of the Side Pin Cushion modulator transistor Q701. The collector of Q701
is connected to the Deflection SW +115V. The DC offset voltage and Vertical parabolic side pin cushion com-
pensation wave form is now super imposed on the SW +115V which is sent to the Deflection Transformer T701
and the Horizontal Linearity circuit C715, L703, R729 to the Horizontal Yoke returns.
D SIZE SWITCH:
When Magic Focus is activated by either the Magic Focus button or customer's menu or during service when the
sensors are initialized, Q710 receives the D Size command from the Digital Convergence Unit, UKDG pin 15 of
PDS connector. When Q710 turns on, it bypasses R714 and lowers the resistance from the emitter of Q701 to
ground. This increases the Horizontal size to allow positive contact of the light pattern hitting the sensors.

X-RAY PROTECT:

If something should fail within the Side Pincushion circuit that could cause a CRT burn, the voltage at pin 7 of
I701 is monitored by D702. If this zener fires because the voltage at it's cathode increases above a specified
level, D703 would forward bias and send a Shut Down command through the Protect line.
(See Deflection Protect Power Supply Shut Down Circuit Diagram for details.)
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