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NOTE
Ensure
that the
bottom
cover
is
in
place
on
the
instrument
when
observing the
signal at
TP
10.
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
TP
10
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/343
A
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.
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