Sage II - Checking the Power Supply; DC Voltage Ranges; Dummy Load Application; Power Supply Adjustment and Replacement

SAGE II
SERVICH MANUAL
[1.0J
CHECKING
THE
POWER SUPPLY
VI CHECKING
THE
POTER SUPPLY
:
Check
power
supply for
these
DC volcage
ranges:
5,0V
=
4.9V to
5.2V
+12.0v
=
11.5v to
13.0v
-12.0v
=
-10.0v
to
-13.5v
If
the
voltages
do not
seem rlght,
or some
are not
there,
external
devlces
from
the
board lncluding
the termlnal,
supply, and
disk
drives.
Apply
a
dumrny load
to
Ehe
powet:
supply
by eonnecting
resistors
from
the
supply
to
ground.
+
5V
=
1.2
ohmn
50
watt
*l2V
=
8.0
ohm
50
watt
-lzV
=
16 ohm
25
watt
dlsconnect any
printer,
power
the followlng
Check
the
po\./er
supply
voltages
again.
If the
voltages are
outslde
of
the ranges
then the
voltage
should
be
adJusted.
(On
the
Compower
power
supply
change the
Rtr16
trlmmer.)
AdjusE:
+
5V
to
between
5.0
to
5.lV
Replace the
power
supply if
this is
not
possible.
Check +12V
for
11.5
Eo
13.0V
-IzV
for
-10.0
to
-13.5V
If the other
voltages
fal1
outside
the limlts
replace the
Power supply.
If
the
power
supply
checks
out
ok, then a
short exists
on the
board, or
on a
perlpheral
belng
powered
from
the
board.
To determlne
which
section(s) have
the short(s), apply
a
5.0v, 3
amp
current lfunlted
voltage to
each
of the three
power
supply
lnputs
on the
cpu
board.
Be
careful
to
observe
correct
polarity.
the
voltage will
drop
on the sectlon
that is
shorted.
Using the appropriate
(usually
most sensltive)
scale
of
a
DW, measure
the
voltage
between the
power
rail
under
test,
and
ground
at
varlous
polnts
on
the
board.
The
points
with the least
voltage across
Ehem
lndlcate
the
area where
the
short is.
In
a new
board the
fault
is
usual.ly
a trace
short
or a
solder brldge; in a
board
from
the
field
the
fault
1s
usually a
bad
chlp.