Sage II - Checking the System Clock; Checking the Address Strobe Line

sAcE
rI SERVICE
I'IANUAL
[1.0]
CPU
BOARD TROUBLESHOOTING
Speclfic
checks
of the lmportant
system
slgnals fo1low.
It
wl11 also
help
to have
a
good
understandlng
of the Boot
program.
Refer to
the
sectlon
on
the B0OT
TEST ln
thls
manual.
VI
I I.
O I
CHECKII{G
TEE
SYSTEIII
CLOCK :
Ctreck
these
polnts
with
an
oscllloscope.
then
look for
the
problem
lndicated.
If
there ls no
8
Mhz
clock
Pln
8
of
Pln
3
of
Pln
15 of
Pin
14
of
Pin
13
of
Pin
10
of
Pln
I
of
u66
u69
u68
tJ44
v37
u37
u54
shorted
crystal
oscillator.
short
or bad
counter
U69
open trace
from
U69-pln
3.
short
or bad buf
f
er
1J44.
open
trace
from
U44-ptn 14.
short
or bad inverter
U37.
I2O
ohm reslstor
misslng or wrong
value
or a shorted
line
Check
for
64
l(hz at
pln
9
of
U75.
If
it ls not
there then
trouble
shoot
counter
chaln
of
U69
and
V67
and/or
check
for
short on
64
ICrz
line.
Check for
54
Iihz at
pln
1l
of
U34. It should
be
there If
lt
was at
U75-
ptn
9.
VIII.02
CHECKING
TEE
ADDRESS
STROBE
LINE :
Check to
see lf
AS+
pin
13
of
If
AS+
is
noE
rlght
then
check
It should
be
high
or
floating
low
check
for
elther
shorts,
a
processors
are
very
rare.)
U44
is
either
low or
toggllng.
pln
6
of
U68
where the
slgnal
orlglnates.
(
if the
processor
is halted).
If
1t 1s
bad
U44,
or
a
bad
processor. (Note:
Bad
If
U68-ptn
6
ls
ok then
check
the lnput
on
pln
17
of
lJ44
for
a high
or
floating
signal.
If
it
ls not
the
same as
U68-pln
6
check for
an
open
trace.
C'heck for a
low
on
Pin
3
of
V44
as the slgnal should
be
lnverted
through
u44.
rf the lnput
on
ptn
17
ls ok, but
pln
3
ls high,
then
elther
the output ls
shorted
or
tJ44
ls
bad.
U44-pln 3
and
U44-ptn
13
are
connected and
should have
the
same slgnal.
If
not
check for
an
open
trace or
a bad
socket.
Check
for
high
at
pln
2 of
Ul5.
U44 may be bad, the reslstor
may
U15
ltself
or
a short
to
another
A low
or
floatlng
state lndicates
that
not
be l2O ohms, or the
trace ts
open.
llne
could
be
the
problem.
T6