Lcd - Fluke 93 Service Manual

3-12
CIRCUIT DESCRIPTIONS
this
way
capacitor
C1312
is
charged
Just
enough
to
keep
the output voltage
-fVRAM
at
a
stable
value
{
3V
DC).
sie*u
Figure
3.
6
Pulse
trein
signal
on
input
A
of Schmitt
input
HAND
(Test Point
223)
3.3.5
LCD
circuitry
•
Introduction
The
LCD
used
in
the
ScopeMeter
is
controlled
by
six
LCD
driver integrated
circuits.
These
drivers get
their
information (data-
and
control signals)
directly
from
the
D-ASIC.
The
microprocessor enables
the display
when
valid
data
is
present.
ScopeMeter models 93 and 95 use
a reflexive
LCD. Model 97
Is
provided
with
atransflexive
LCD
with
a
backlight,
which
can be
switched
on
or
off
by the
user.
•
Detailed
circuit
description
See
figure circuit
diagram A1
(figure 10.2),
LCD
The ScopeMeter
uses
a Super Twisted Nematic
Liquid Crystal
Display
(LCD
HI 401. see
circuit
diagram
A1, figure 10.2), with a resolution of
240
*
240
pixels.
The
picture
on
the
LCD
screen
is
written
column
(vertical
line)
after
column, rather hian
row
(horizontal
line)
after
row.
The
LCD
screen
is
divided
horizontally
In
3 row-sections,
each
60
pixels
wide
and
vertically into
3
column-secUons,
each 60
pixels wide.
LCD
drivers
The
LCD
display
is
controlled
by
the
D-ASIC,
via
six
LCD
drivers:
-
three
LCD
row
drivers:
D1404, D1406,
D1407
>
three
LCD
column
drivers:
D1401, D1402,
D1403
Description of the
LCD
drivers lnput-/output signals:
LCD
outputs
Yt...
YSO
and
X1...XS0
These
outputs are
connected
to
the
LCD
matrix.
Every column
driver serves 80 pixel
columns
of the
LCD.
Every
row
driver
serves 80
pixel
rows.
The
output signals
are
staircase
signals, with levels
equal
to
the
VI
...V6
voltages.
NOTE:
On
the
ouput
of every
LCD
driver,
a
Test Point
is
provided (TP207...TP212).
When
the driver
is
working
property,
a
staircase voltage
can be
measured on
these
test points.
•
Data inputs D0...D3 (row
drivers only!)
The
actual display
data
coming
from
the
D-ASIC
is
sent
via
the
DRIVERBUS
to
the
LCD
drivers
D0...D3
inputs.
•
Terminai input voitagee V1...V6
Out
of
these
DC
signals, with
^
-20
V,
the
LCD
drivers
generate the staircase
signals.
The
input
voltages Vi...ve are generated by die
LCD
supply
section.