Trigger Pulse - Hitachi 51SWX20B Training

DP-2X VERTICAL OUTPUT CIRCUIT EXPLANATION
(See the DP-2X Series Chassis Vertical Output Circuit for details)
I601 B+:
The Vertical Output IC I601 requires SW+28V to operated. This voltage is supplied from the Power Supply. The
output for the SW+28V pulse is from pin 14 of T902. This power supply is protected by E902, rectified by
D918, filtered by C929, L913, C950 and output from the PPD6 connector pin 1 and 2. It arrives at the Deflection
PWB and is routed through the Vertical B+ Excessive Current Sensor R629, Q604 to pin 10 of I601.

TRIGGER PULSE:

The Trigger pulse is routed from the Rainforest IC I401 pin 27 on the Signal PWB. It is output from the PPD2
connector pin 10, through the Power Supply PWB and then through the PPS2 connector pin 10 to the Deflection
PWB. It is then sent to the Trigger Input on I601 pin 3.
During Trace, the internal Ramp Generator circuit using C603 connected to pin 7 as the time constant begins
charging. As it charges, the Pump Up circuit is also charging from the SW+28V to C605, through pin 11 to an
internal switch of I601. When the Trigger pulse arrives (Retrace Time), the internal switch toggles over to the
output stage push pull pair inside I601, and the +28V charged capacitor C605 discharges. The output stage push
pull pair inside I601 already have +28V input from pin 10. So the output pulse from pin 1 is now near 50V p/p.
This is only needed for a short duration of time, (retrace) so the Charge Pump circuit eliminates the need for a
50V power supply.
(V BLK) VERTICAL BLANKING PULSE GENERATION:
When the Charge Pump discharges and produces the 50V p/p pulse for Vertical drive during retrace, this pulse
from pin 11 is also routed out as the Vertical Blanking pulse. It's amplitude is around 21V p/p and is sent to the
following circuits;
•
Vertical Sweep Loss detection circuit
•
Convergence circuit for vertical correction waveform generation
•
To the PPS2, PPD2 connector pin 12 to be sent to various circuits on the signal PWB. The Micro-
processor uses this signal to time it's OSD.
VERTICAL OUTPUT PULSE:
The Vertical Output pulse is then routed to the Vertical Yokes generating a linear sawtooth current which moves
the beam. (Trace = from top to bottom, Retrace = from bottom to top). This linear current is generated by the
charge time constant of the vertical yokes charging C607 through the low ohm resistors R619, R620.
VERTICAL YOKE CHARGE PULSE:
The pulse generated on the positive side of C607 is also routed through the parabolic wave form generation cir-
cuit of R621, and C608 to the side pincushion circuit and to the dynamic focus circuit for corrections to deflec-
tion and focus.
The pulse generated on the positive side of C607 is also routed back to I601 pin 8 and 9. The AC component of
this signal is for vertical linearity compensation. The DC component of this signal and the DC component pro-
vided by the Vertical size pot into pin 4 are routed back to the Ramp generator circuit described above. The DC
component determines the charge time associated with the ramp generator or in other words, the Vertical height.
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, Q603 receives the D Size command from the Digital Convergence Unit, UKDG pin 15 of
PDS connector. When Q603 turns on, it bypasses R611 and lowers the resistance from R607 (Vertical Size Pot)
to ground. This increases the Vertical size to allow positive contact of the light pattern hitting the sensors.
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