Fluke 341A - Page 37

NOTE
Ensure
that the
bottom
cover
is
in place on the
instrument
when
observing the signal at TP10.
The
top
cover should be
slid back just
far
enough to admit
the probe.
f.
Set the
oscilloscope input
to ac, vertical
sensitivity to
0.02
volts per
centimeter and
sweep speed to 1 milli-
second
per
centimeter.
g.
Compare display
with the
waveform shown in Figure
4-7,
which
indicates
proper
adjustment of
spike
compensation
control R162.
The signal is
acceptable
if
the positive and
negative spike
amplitudes are less
than
0.3 volts.
Figure
4-7. CHOPPER AMPLIFIER
SIGNAL
-
TP10
be
necessary
to perform
the
10
volt
zero
and
range
adjustments,
paragraphs
4-65
and
4-67
(paragraphs
4-74, 4-79,
and 4-83
for
the
Model
343A).
~
FAULT
ANALYSIS
(!)
If signal at
TP9 is not
correct, check for
square
wave signal at the
collector of
Q2.
Transistor
Q39,
Ql, Q2
or
Q3
may
be
defective.
(2)
If the signal
at TP10 is not
correct, inte-
grated
circuit IC1 or MOS
FET transistor
Q38
or 039
may be defective.
449.
SERIES
REGULATOR
4-50. This test
verifies proper operating
voltages for the
control
transistor
and preregulator
transistors.
a.
Set Model 341 A/343A
controls as
follows:
FUNCTION
ON
RANGE
Voltage dials
10
10 .00000
(Model 341 A)
10.000000 (Model 343
A)
CURRENT
LIMIT Fully
clockwise
h. If
the signal obtained in
step
g.
is not acceptable, it
will be necessary to
adjust
R160
and
R162.
Proceed
as
follows:
(1)
Set chopper
drive control
R160 fully clockwise.
(2)
Adjust
R162 for
minimum spike
amplitude.
A
point
should be found
where the
positive and
negative
spike
amplitudes are
approximately
equal and nulled.
(3)
Rotate chopper
drive control R160
counter-
clockwise until
noise spikes begin
to appear in
the formerly
quiet regions.
(4)
Reverse the
adjustment of R1
60
just far enough
to restore
the quiet region.
(5)
Repeat step
g.
NOTE!
Adjustment
of
R160
and R162
affects
the out-
put zero on the 10
volt range; therefore
,
it
will
b.
Connect the 895A
between the
metal case (collector)
of
Q40
and the
+
OUTPUT terminal.
The voltmeter
should
indicate between 10 and
13.5 volts dc.
c.
Connect a
400 ohm
±5%,
1
watt resistor to
the
OUTPUT
terminals and
connect the
positive
OUT-
PUT terminal
to chassis
ground.
d.
Using the 853A
multimeter,
measure
and
record the
collector-to-emitter
voltages
of
each series
regulator
transistor,
Q48, Q46. Q44,
and Q42.
The voltages
should differ by
less than 25 volts dc.
—
FAULT
ANALYSIS
(1)
If the collector
voltage of
Q40
is not
within
limits, zener diode
CR48
is
prob-
ably
defective. Also
check transistors
Q40,
Q42
and Q43.
(2)
If
the
voltage
division across the
preregis-
lator is not
equal within
2S volts, check
transistors
Q42
through Q49
and
check
for a
change in
value of resistors
R58,
R60, R61, or
R64.