Refit
the cover
and
the cord.
Power
up.
If
the
unit
still
does
not
power
up
or
if
a fuse
blows
once again,
refer
the problem to
an
authorized
service
technician or
return
the
unit
to Lexicon.
5.2
SERVICE
PRELIMINARIES
If
the
field
service
is
attempted,
first
verify
the operation
of
all
power
supplies.
A convenient place to probe
power
supplies
is
at
their
chassi~
mounted
three-pin
regulators,
U68,
U69,
and
U70.
Their corresponding
volt-
ages
are
printed
on
the
circuit
board near the appropriate leads.
Use
the
chassis
as a ground reference
and
take care
when
probing
that
the probe
does
not
short
adjacent leads
of
the
regulators.
See
FIG.
5.0 to
identify
these
test
points.
The
following
table
indicates
appropriate voltage
limits:
LIMITS
REGULATOR
VOLTAGE
MIN.
MAX.
U68
+5V
4.75V
5.25V
U69
+15V
14.25V
15.75V
U70
-15V
-14.25V -15.75V
NOTE:
If
both
memory
and
analog subsystem
modules
are
removed
from
the mother-
board, the analog
(±15V)
ground
and
the
digital
(+5V)
ground
become
isolated.
This
means
that
correct
voltage readings are obtained only
when
measuring with
respect
to the corresponding ground.
Do
not
remove
modules under
power.
Should
module
removal
be
required proceed as follows:
Each
module
is
held in place
by
four nylon standoff
retainers.
Each
retainer
has
a small locking barb
which
must
be
depressed with needle
nose
pliers
or
screwdriver while
carefully
lifting
the
circuit
board
at
the nearest corner.
Release
one
corner
at
a time
and
then
lift
the
entire
module
from
the mother-
board.
Installation
of
circuit
boards require alignment
of
all
connector pins with
their
mating
receptacles.
After positioning board, firmly press each corner
until
all
lockin,g barbs are engaged.
L
57
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