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Section Vlll
SERVICE
GROUP
C
Model 3455A
e.
Unable
to
adjust
100
V
at
40 kHz,
within
limits:
Moving
the wire
connecting
the
R92, C29,
and
C32,
C34 modes away
from
the
shield,
may
raise
the reading.
f.
The
100
V
and
1000
V
ranges
inaccurate:
The R92 and R93
resistor
divider
may
have changed
value.
K1
-
K3
contacts
may
be
resistive.
g.
Overload
indication
with
a
1000
V
at
1
kHz
to
10
kHz
sinewave applied
to
the
input:
AlOKl,
K2,
or
KS
may
have developed
leakage.
The
leakage
can be
isolated
by removing
the
orange
jumper
from
the
froni/rear switch
connected
to
K1 and
KS.
If
the
overload condition
disappears,
KI
or
K5
may
be
defective.
If
the
overload condition remains,
remove
the
jumper from
K2
and
connect
the
jumper
directly to
the input
of
the
AIS
board.
If
the
overload condition
disappears,
K2 may
be
defec-
tive.
h.
1
V
and
10
V
ranges inaccurate
and
out
of
calibration;
A1SK3 may
be
shorted.
i.
Full scale
readings
go
high with
an
increase
in
temperature:
A1SQ9
or
Ql
1
may
be
defective.
j.
1500 counts
error
on
the higher
ac
ranges:
Connect guard
to
low.
k.
Differences
in
high frequency readings
between
the front
and
rear
input
terminals:
Short
the
rear terminals'
guard
to low.
l.
The
ac
convertor should be
calibrated
with the
guard
cover
in
place.
8 C-17.
Average Responding
AC
Convertor (Schematic
2).
8-C-18.
Due
to the simplicity
of
the
average responding ac
convertors,
only
a
few
pertinent
troubleshooting
hints are given.
a.
Component
location
and
layout
may
be
critical
to
the
convenor's
freqency response.
Capacitors,
especially
in
the
input
circuit,
should
not be too
close or
too
far
from
(he
PC
board.
Make
sure (he
relays
are
not touching
the
ground
plane.
b.
The
ac
convertor should be
calibrated
with
the
inguard cover
in place.
c.
A13Q15,
U4, US, and
associated
circuitry
may
occasionally
fail.
d.
To
help
flatten
the
frequency response of
the
convenor,
especially
at
10
kHz,
C2S
is
usually
padded
with a 33
pF
capacitor
(pad
list
in
the parts
list).
If
unable
to
bring the
level
down
at
10
kHz,
a
28
pF
capacitor
may
be
used.
e.
To
help
in
troubleshooting the ac convertor, the following checks
can
be
made.
1
.
Apply
a
I
V, 100
Hz
sinewave
to
the input
of
the
345SA,
with
the
instrument
set
to
the
1
V
range.
2.
US
pin
6 should have
a
1
V
peak
to
peak sinewave
and
TPl
should have
a
S
V
peak
to
peak
sinewave.
3.
A
6.67
V
dc
voltage
should be read
at
TP2.
If this
voltage
is
good and
there
is
an
incorrect
reading
on
the
display,
A10Q3 may
not be turned
on
or
may
be
defective.
8-64
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