Date : 10/02/98 R7621127
Sync+Vertical Deflection
R7621127
20
Technical description
The vertical scan fail circuit is the same for the three deflection output circuits. We
limit the discussion to the green output.
The feedback across the feedback resistor R145 is capacitively coupled to the base-
emitter of Q22. The conduction time of this transistor is only during the positive
portion of the ramp and is determined by the amplitude of the vertical ramp. By the
capacitor the shift voltage is removed and does not play a role in the scan fail
detection. The (integrated) collector voltage across C102 is thus inversely proportion-
al with the amplitude of the sawtooth. As long as the amplitude is acceptable, the
collector voltage is sufficiently low to block Q23.
Either one of the scan fail circuits can saturate Q23 to "cause" the scan fail condition.
3. EAST-WEST CORRECTION
a. Trapezoidal distortion
(sheet 2 of the Subunit schematic).
V SWT
signal with C440, the amplitude is reduced to match the Bella specifications.
The OPAMP inverts the ramp and the output produces a sawtooth that is
symmetrical around the zero level, since the non - inverting input is at ground level.
Two ramps labelled
+ / - V SWT
are available for adjustment by the "0" potentiometer
in the Bella IC402. The output is labelled
" %V SWT"
(adjusted Vertical Sawtooth).
b) Pincushion distortion.
For the pincushion correction a vertical parabola is required. This parabola is
generated by the multiplier IC410 . The
-V PAR
output pin 1 of the OPAMP together
with he inverted
+ V PAR
feed the potentiometer " 1 " in the Bella IC402. The output
is labelled
"% V PAR"
(adjusted Vertical Parabola).
c) Line frequency dependent correction - Power Amplifier
(sheet 1).
The adjusted waveforms are added with R424 / R425 and then passing the capacitor
C422. A small DC voltage obtained from R446/R447 is added to the signal. This small
DC voltage undergoes the same gain of the E/W waveform.
The output is passed on to a Miller integrator to remove the waveform and check the
gain of the OPAMP. On the other input we apply a portion of the line frequency
depHTHD voltage.
The gain of the OPAMP depends on the feedback ratio R445 / Q401. The gate bias
of the latter is the output voltage of the integrator. As this voltage is line frequency
dependent the gain of the OPAMP follows the value of the HTHD voltage. Note that
the +HTHD voltage is not exactly proportional with the line frequency. However, the
East / West correction always must be related to (a certain percentage of) the hor.
scan voltage.
Depending on the ceiling / table position, the maximum E/W correction is at the top
or the bottom of the screen. The feedback time constant between gate and source
is adapted accordingly. In table position
VSI
is low level and Q405 is on. R471/C444
is added to the R442/C446 time constant.
If the projector is mounted ON-AXIS, J400 link must be removed as in this case there
is no E/W correction needed.
The output of the OPAMP, pin 1 (E/W CORR) is sent to the main unit via J403(9)
where it is amplified with IC10, a TDA2030 power amplifier. It reaches finally the UN
HOR DEFL to modulate the scan vHTHD.
4. Horizontal oscillator Autolock
Phase alignment
(on the main board)
a) Horizontal osci Autolock
The DC is removed from the
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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