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Epson PX-8 - Page 83

Epson PX-8
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REV.-A
2.5.1.3
J3
J3
is a maintenance purpose
jumper
used
for
testing
the
sub-
CPU
7508.
To
open (set off)
this
jumper,
put
the
jumper
block
as
shown
in Fig.
2-62;
leaving one
terminal
pin open.
OFF
is
the
standard
setting.
The
ON
setting
disables
the
normal sub-
CPU
operation.
2.5.1.4
J4
~~------------~~
Fig.
2-62
Jumper
J4
allows
for
pull-up
of
the
analog
input
(ANIN) signal input. Because
the
ANIN
signal
input
voltage
ranges
from
0
to
+2.0V,
the
jumper
may
need
to
be reset
depending
on
the
connect-
ed
analog device.
2.5.1.5
J5
Jumper
J5
is used
to
eliminate
vertical
ghost
display
lines
which
may
appear due
to
the
charac-
teristics
of
the
LCD unit. Its
setting
depends on
the
installed LCD
unit
(or
the
LCD panel,
to
be
precise).
J5
may
need
to
be reset
when
the
LCD
unit
is replaced
so
that
ghosts,
if
observed,
are eliminated.
2.5.2
Switches
Five
switches
are
mounted
on
the
MAPLE board as
shown
in Fig.
2-61.
Their
functions
are de-
tailed in
the
following.
2.5.2.1
SW1
This
switch
is used
to
turn
the
computer
on and off.
It
is
connected
to
a
port
of
the
sub-CPU
7508
which
controls
power
on/off
by sensing a
setting
change
of
this
switch.
Thus,
it
may
be in-
effective
when
the
sub-CPU loeses
the
normal
power-on/off
sequence
control
capability
because
the
computer
can,
through
a
programming
error,
got
into
a
software
loop.
2.5.2.2
SW2
This
is
the
RESET
switch
which
is accessible at
the
left
side
of
the
computer.
It
is
connected
to
another
port
of
the
sub-CPU. The
switch
causes all
of
the
computer
sections
except
for
the
sub-
CPU
to
be initialized,
it
is
ineffective
when
the
sub-CPU is
not
operating
normally.
2.5.2.3
SW3
This
switch
allows
the
user
to
enable
or
disable
the
charging
and
discharging
circuits
for
the
auxi-
liary battery, soldered on
the
MAPLE board.
It
is provided in
order
to
prevent
complete
auxiliary
battery
discharge
and
thereby
protect
the
battery
from
deterioration
when
the
PX-8
unit
is
stored
unused
for
a
long
period
of
time. The
switch
must
be set
ON
whenever
the
board is in service,
otherwise,
the
normal backup operation
would
not
be in effect.
After
a
low
voltage
condition
is
detected,
the
Ni-Cd
battery
life is shortened
if
left
completely
discharged.
2-59

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