Date : 10/02/98 7621065
SM POWER StBy
7621065
13
SUB MODULE
762106S
pletely transferred to the secondary side. By this measure, the current through
the power switch is reduced to a minimum.
Secondly
, the negative amplitude is rectified by D111 and compared with the
reference 4 volts that is available at pin 1.
The error voltage is now sent to pin 3 and serves as a control voltage to adjust the
duty cycle and frequency of the switcher.
The same windings also serves as a help at starting up. This windings provides
energy the moment the P22-P24 winding does not. The rectified voltage passes to
pin 9 up to the moment that pin has reached 12volts.
The current through the power switch is at all times checked and if too high (in the
event of a short on the secondary side) the comparator 393 (IC101) output drops
the error voltage in order to adapt the duty cycle of the switcher.
Note that aspecial winding is provided, delivering
+17M
, or, a voltage related to the
Mains
ground and not the chassis ground. This voltage is utilized on the EHT board,
because the drive circuit for the power switcher is Mains ground and not Chassis
ground. (see description EHT board).
Generation of the +HTHD volt-
age (scan voltage).
This voltage is linked with the horizontal deflection board as it has to be adapted
to the scanning frequency. A feedback voltage (FBHD) is for that reason arriving on
the subunit.
This feedback voltage, at contact J4(7) of the subunit, is sent to the base of the error
amplifier Q6. The potentiometer P2 allows an adjustment of this feedback, or in
other words, the horizontal width can be aligned with P2.
The emitter of Q6 is set at a reference zener voltage, adjustable with the voltage at
the regulating pin of Z8. This voltage is the result of the output of the DC-amplifier-
buffer 353, combined with the +HTHD voltage.
By this measure, we reduce the range of the horizontal width at high scanning
frequencies. Indeed, at standard video frequency we need much more range to
overscan.
The collector current of the regulating transistor Q6 flows into the opto-coupler IC5
and the phototransistor of this insulating device is now regulating the DC voltage at
pin 3 of IC100, in order to stabilize the +HTHD voltage for one typical line frequency
and amplitude setting.
Q7 is a 5mA current generator and D10 a
green
LED to visualise the +HTHD
voltage.
Pin 2 of the 393 (IC4) is set at 5.6 volts with Z10 and, the other input, pin 3 is the
scan voltage divided by R38/R39.
As soon this input exceeds the zener voltage, the output switches high and
saturates transistor Q9. The +HTHD voltage is dropped to a low level.
The original overvoltage protection is now is causing an under voltage protection.
Overvoltage protection.
Technical description
Summary of Contents for GRAPHICS 1209S
Page 4: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC SAFETY NOTICE...
Page 9: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC GENERAL INFORMATION...
Page 28: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC SERVICE SHEETS...
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Page 157: ...Date 10 02 98 762457 Deflection Switching Module 762457 1 SERVICE SHEET...
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Page 307: ...Date 18 06 96 R762284 Power mains input module R762284 1 SERVICE SHEET Rev 01...
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Page 339: ...Date 10 02 98 R7627591 Frame cpl R7627591 1 SERVICE SHEET R806430...
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Page 354: ...Date 10 02 98 R761781 IR Receiver module R761781 1 SERVICE SHEET IRRECEPTION IRRECEPTION...
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Page 359: ...Date 10 02 98 R762510 IR RS 232 Communication module 1 R762510 SERVICE SHEET...
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