Daewoo DUB-2850GB Service Manual page 44

CP-780 Service Manual
is obtained when the VID bit is set to 0 . When the VID bit is 1 the mode of the first control
loop can be switched by means of the FOA/FOB or POC bits.
For a good performance during normal TV reception (display of the front-end signal) various
connections are active between the vision IF amplifier and the synchronisation circuit (e.g.
gating pulses for the AGC detector and noise gating of the sync separator). These connections
are not allowed when external video signals are displayed. The switching of these connections
can be coupled to the input signal selection bits (INA-IND). This mode is obtained when the
VDXEN bit is 0 . Due to the input signal selector configuration it is possible that the internal
CVBS signal is available on one of the other CVBS inputs. In this condition the connections
between the vision IF amplifier and the synchronisation circuit can be switched on and off by
means of the VDX bit. The VDXEN bit must be set to 1 for this mode.
The vertical synchronisation is realised by means of a divider circuit.
5.2.7 Horizontal and vertical drive
The horizontal drive is switched on and off via the soft start/stop procedure. The soft start
function is realised by means of variation of the TON of the horizontal drive pulses. During the
soft-stop period the horizontal output frequency is doubled resulting in a reduction of the EHT
so that the picture tube capacitance can easily be discharged. In addition the horizontal drive
circuit has a low-power start-up function.
The vertical ramp generator needs an external resistor and capacitor. For the vertical drive a
differential output current is available. The outputs must be DC coupled to the vertical output
stage.
The IC has the following geometry control functions:
* Vertical amplitude
* Vertical slope
* S-correction
* Vertical shift
* Vertical zoom
* Vertical scroll
* Vertical linearity correction. When required the linearity setting for the upper and lower part of
the screen can have a different setting.
* Horizontal shift
* EW width
* EW parabola width
* EW upper and lower corner parabola correction
* EW trapezium correction
* Horizontal parallelogram and bow correction.
When the East-West geometry function is not required (e.g. for 90 picture tubes) the EW output
pin can be used for the connection of the AVL capacitor. This function is chosen by means of
the AVLE bit.
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