Mitsubishi DPLUS 74SB -BKA Service Manual page 129

I²C-bus autosync deflection controller for PC monitors
Adjustment of vertical position, vertical linearity and ver-
tical linearity balance
Register VOFFS provides a DC shift at the sawtooth out-
puts VOUT1 and VOUT2 (pin 13 and 12) without affecting
any other output waveform. This adjustment is meant for
factory alignments.
Register VPOS provides a DC shift at the sawtooth output
VOUT1 and VOUT2 with correct tracking of all other re-
lated waveforms (see Section "Tracking of vertical
adjustments"). This register should be used for user
adjustments. Due to the tracking the whole picture moves
vertically while maintaining the correct geometry.
Register VLIN is used to adjust the amount of the vertical
S-correction in the output signal. This function can be
switched off by control bit VSC.
Register VLINBAL is used to correct the unbalance of ver-
tical S-correction in the output signal.
Tracking of vertical adjustments
The adjustments via registers VSIZE, VOVSCN and VPOS
also affect the waveforms of horizontal pincushion, vertical
linearity (S-correction), vertical linearity balance, focus
parabola, pin unbalance and parallelogram correction. The
result of this interaction is that no readjustment of these
parameters is necessary after an user adjustment of verti-
cal picture size and vertical picture position.
Adjustment of vertical moire cancellation
To achieve a cancellation of vertical moire (also known as
'scan moire') the vertical picture position can be modulated
by half the vertical frequency. The amplitude of the modu-
lation is controlled by register VMOIRE and can be switched
off via control bit MOD.
Horizontal pincushion (including horizontal size, cor-
ner correction and trapezium correction)
EWDRV (pin 11) provides a complete EW drive waveform.
The components horizontal pincushion, horizontal size,
corner correction and trapezium correction are controlled
by the registers HPIN, HSIZE, HCORT, HCORB and
HTRAP.
The corner correction can be adjusted separately for the
top (HCORT) and bottom (HCORB) part of the picture.
The pincushion (EW parabola) amplitude, corner and tra-
pezium correction track with the vertical picture size (VSIZE)
and also with the adjustment for vertical picture position
(VPOS). The corner correction does not track with the hori-
zontal pincushion (HPIN).
Further the horizontal pincushion amplitude, corner and tra-
pezium correction track with the horizontal picture size,
which is adjusted via register HSIZE and the analog modu-
lation input HSMOD. If the DC component in the EWDRV
output signal is increased via HSIZE or Ihsmod, the
pincushion, corner and trapezium component of the EWDRV
output will be reduced by a factor of

+ 
V V
HSIZE HEHT

1 −
14.4V
The value 14.4V is a virtual voltage for calculation only.
The output pin can not reach this value, but the gain (and
DC bias) of the external application should be such that the
horizontal deflection is reduced to zero when EWDRV
reaches 14.4V.
HSMOD (pin 31) can be used for a DC controlled EHT com-
pensation by correcting horizontal size, horizontal
pincushion, corner and trapezium. The control range at this
pin tracks with the actual value of HSIZE. For an increasing
DC component V
HSIZE
component V caused by I
HEHT
V
HSIZE
−
1
factor of
14.4V
The whole EWDRV voltage is calculated as follows:
V = 1.2V + [V
EWDRV HSIZE
×
V + V ) g(HSIZE, HSMOD)]h(I
HCOR HTRAP
I
HSMOD
= ×
V 0.69
HEHT
120µ2
V
HSIZE
= −
f(HSIZE) 1
14.4V
( )
g HSIZE, HSMOD =
I
HREF
h(I ) = 1 −
HREF
I
HREFf
7-28
TDA4857

H
HSIZE
− 
1
14.4V 
in the EWDRV output signal, the DC
will be reduced by a
HSMOD
as shown in the equation above.
×
+ V f(HSIZE)+(V
HEHT
HREF

V
+  −
V V 1
HSIZE HEHT

1 −
14.4V
=
70kHz
+
HPIN
) where:

HSIZE

14.4V 