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Model 3455A
Section VIII
SERVICE
GROUP
F
8
F-1.
OUTGUARD
LOGIC
TROUBLESKOOTING
(SCHEMATIC
8. 9.
10).
8-F-2.
Outguard
logic
troubleshooting should be
done
using the Signature Analysis Routines
(SA)
in
Figures
8-H-20
to
8-H-27.
If
any
incorrect signatures are
observed,
the
following checks
may
be
helpful.
a.
If
any
incorrect signatures are
observed check
for
a
I
^F
capacitor across
AIU49.
Install
one
if
missing
(part
number
0180-0291).
The
capacitor
should be
installed to
the
underside of
the
A1
motherboard,
with
the
+
terminal
to
pin
14
of
U49
and
the
•
terminal
to
pin 7
of U49.
b.
If
no
stable
signature
can be
located
and
the
A3
board
has been
replaced,
check
the
IC
signals.
Make
sure they are toggling
with
good
logic
highs
and
lows (approximately
4
V
peak
to peak).
c.
Check
for the
waveform shown
below
at
the junction
of
A1C29
and
R42.
If
this
signal
is
miss-
ing,
C29
may
be
defective.
U48
may
also
cause
the missing
signal.
2
V
I
V
(4—3
1.4
msec-
O
V.
8
F-3.
Main
Controller
Troubleshooting (Schematic
8).
a.
Data
lines
D0
to
D7
(pins
1
8 to
25
of
U3U9)
and program
address
lines
P
A0
to
PA9
(pins
1
to
8
of
U9)
should have
voltage
levels
approximately
+
4.5
V
peak
to
peak.
Check
for
any
circuits
that
may
cause
loading.
b.
Sharp
peaks of
3
V
to 3.5
V
may
be observed
on some
lines
of
the processor
(A3U9).
This
is
normal.
The
peaks
are present
when
the processor
is
in
a
tri
state
mode.
c.
Check
the
back
gate
bias voltage
(G.B.)
of
the
outguard
processor
(A3U9).
If
the voltage
is
dif-
ferent
from
the voltage
marked on
the processor (by
±
.35
V) check
for the correct
value
of
the
pad-
ding
resistor
A3R3.
If
R3
is
the correct value
and
the bias
is
incorrect,
replace the
A3
board.
The
cor-
rect
value
of
R3
is
listed in
the
following
table.
G.B.
A3R3
•hp- Part
No.
•5.0
V
4.64 kO
0698-3155
-4.5
V
2.87 kn
0698-4436
-4.0
V
1.96 kR
0698-0083
-3.5
V
1
.00 kO
0757-0280
•2.5
V
715
n
0698-3700
8
F-4.
Front Ponol Troubleshoot
ng.
8-F-5.
Front Panel Oporotion Check.
a.
Turn
the
3455A
off.
Place the instrument
in
the
SA
mode
by
disconnecting the
test
jumper on
the
A3
board and
disconnect the plug
from A1J7.
b.
Turn
the
3455A
on.
Half of
the
instruments
from
panel
LEDs
should
alternately
turn
on and
off with the other
half.
c.
At
the
time
the
instrument
is
turned
on and
half the front panel
LEDs
turn on, a
0 should be
in-
dicated
on
the
left
side
of
the
display.
The
0 should
move
one
position to the
right
each time
the
LEDs
change.
When
the
0
reaches the
far right
of
the
display,
a
.0 will start
at
the
left
and
move
to the
right.
8-73
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