Section
VIII
SERVICE GROUP 0
Model
3455A
for
60 Hz line frequency. If (he
signal is nonexistam,
check
for
an approximately 3
V peak
to
peak
signal at AI0U33
pins 9
and
12. If there is a
signal
at
these pins, troubleshoot the
circuit
between
the
outputs of A10U33
and the secondary
of A12T1.
d. If there is no
signal at AIOU33 pins 9 and 12,
make sure the
divider
U31 and U33
are operating
correctly. Also make sure U33 is enabled
by
line
HI06. The inguard logic
(Latch
U12)
may Im defec-
tive.
if the HI06 line is
low.
e. If all the
above checks are good
and
the
power supply
voltages at A12TP
-
V
and TP +
V are
good, the
other ohms circuits may be
defective.
Troubleshoot the ohms circuits on the
AlO mother
board first. Make sure the
correct relays and FETs are
turned on. Troubleshoot the
current amplifier
circuit and the
voltage clamp amplifier circuit or
the ohms
convertor
board.
8
0-8. Miieellaneout Ohms
Troubleshooting Hints.
a.
Table 8-D-l may be
helpful
in
troubleshooting
various ohms malfunctions. The table
gives
various gain and reference
resistor connections for ail the
ohms ranges.
b. 1 K range to 10 K
range
inoperative; Check for the correct
operation of A10Q13.
c.
100
K
range to 10 M range
inoperative: Check for (he
correct operation A10QI4.
d. 2
wire ohms and 4
wire
ohms
not zeroing properly and
the reading changes 100 counts
when the
3455A is tapped;
Check for a dirty front/rear
switch.
e. 10
K and 10 M ranges
read low: Check AKXJ27,
Q22,
or U3.
B-D-9.
Ohffls Offsets.
8-D-lO.
The following information
may
be
helpful in
isolating ohms offsets. Again,
make sure the
3455A
works correctly in dc.
a. If there is a
150 counts to 200 counts
offset on the 1 K ohm range,
check A10K9. This relay
should only be
closed when the reference
resistor is measured. If the 1
K ohm reading is
low
K9 may
always
be open.
If (he reading is high,
K9 may be shorted.
Table 8-D-1. Ohms Gain and
Switch Configuration.
Range
Ref Ref Unk Res
1 V V Unk Relays
Unk Res
In K Ohms
Res Gain Gain
(fs) Ref (fs) Closed
forV L
0.1 1 K X10
XI
00
.7 mA
0.7 0.07 K7, 8 (>
K)
1 1 K
X10 X10 .7
mA 0.7 0.7 K7, 8 (>
K)
10 1 K X20
X2 .5 mA
0.5 5 K7, 8 (> K)
100 1
M
X2
X20
5
^A
0.5 K8 0 (> 0)
1 K 1 M X10
X10 .7
,iA 0.7 0.7
{>
Ml
10 K 1
M
I
X20 X2
5/xA 0.5 5
(> Ml
f»:
denotes full-scale
2 Wire Ohm: K2.
K4 Closed
VL: denotes Voltage
Limited 4
Wire
Ohm:
K3 Closed
b. A
quick offset check: Short either
AI0R59 or R61 and
observe
the
reading of the 3455A. If the
offset
disappears
with
RS9 shorted. A10Q13
and its associated circuitry
may be leaky or
defective.
If
the offset disappears
with R6I shorted. AI0Q14
and its associated circuitry
may be leaky or defec-
tive.
c. If there is
an offset
on
the 1(X) K ohm range,
remove the blue
wire
connected to
A10R59. If the
offset
disappears, QI3 may be leaky.
8-66
To Next Page
Loading...
