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4-51.
CONTROLLED CURRENT
LIMITER
4-52.
This
test
verifies
proper
limiter
operation
and
determines the current control
range.
a.
Set
Model 341A/343A
controls
as follows:
FUNCTION
ON
RANGE
10
Voltage
dials
10.00000
(Model 341
A)
10.000000
(Model
343 A)
CURRENT
LIMIT
Fully clockwise
b.
Connect
the
853A,
set
to the
100
milliamp
range, to
the
OUTPUT
terminals.
The LIMIT
ON
lamp
should
illuminate
and
the
85
3
A
should
indicate
between 25
and
36
milliamps.
c.
Set
the
CURRENT
LIMIT
control
fully
counter-
clockwise.
The
range
of adjustment
should
be
approximately 30
milliamps.
d.
Set
Model
341 A/343
A
controls
as
follows:
FUNCTION
ON
RANGE
1000
Voltage
dials
100.0000 (Model 341 A)
100.00000
(Model
343A)
e.
Adjust
the
CURRENT
LIMIT
control
through
its
range,
while observing the
853A.
The
range
of
adjustment should be approximately
34
milliamps.
FAULT
ANALYSIS
If
controlled current range
is
not
sufficient,
check
+15
and
-15
volt
supply output
voltages
and check
transistors
Qll
and Q12.
4-53.
CROWBAR
4-54.
In
the following
test,
crowbar
circuitry
is
exer-
cised
by
short-circuiting the
output and
by
down
ranging
the
instrument
excessively.
a.
Set
Model
341 A/ 343
A
controls
as
follows:
b.
Short
circuit
the
OUTPUT
terminals,
and
set
the
voltage
dials
to
300.000 (300.0000
on
the
Model
343
A).
The
LIMIT
ON
lamp
should
illuminate,
and
the instrument
should
trip
to
STANDBY.
c.
Remove
the short
from
the
OUTPUT
terminals
and
reset
the instrument.
The LIMIT
ON
lamp
should
extinguish,
and
the
ON
lamp
should
illuminate.
d.
Set the voltage
dials
to
1000.000 (1000,0000 on
Model.
343A), and then
downrange
the instrument
by
setting
the
RANGE
switch to 100.
The
crowbar
relays
K2A
and
K3A
should operate
several
times
very
rapidly,
or
rattle,
as the
RANGE
switch
is
changed.
e.
Repeat
step
d
several
times,
allowing
at
least
5
seconds
between
range changes.
f.
Repeat
step e several times,
allowing only
2
seconds
or
less
between
range
changes.
The
instrument
should
trip
to
standby.
FAULT
ANALYSIS
(1)
If
instrument does not
trip
to
STANDBY
when
the
OUTPUT
terminals
are
shorted
at
300
volts
output,
check
the
Schmitt
trigger
input
(voltage across
R89).
This
voltage
should
be
at
least
6
volts to
trig-
ger
the
Schmitt
circuit.
If
input
is
cor-
rect,
check
other Schmitt
trigger
compo-
nents,
especially
transistor
Q31,
zener
diode
CR55,
and
relays
K2B
and
K3B.
Also,
check diodes
CR6, CR8, CR29,
CR66
and
CR67.
(2)
If
the
crowbar
relays
do
not
rattle
when
the
instrument
is
downranged from 1000
volts,
check
for
proper operation of
the
Schmitt
trigger circuit.
(3)
If
instrument does not
trip
to
STANDBY
when
it
is
downranged
repeatedly
as de-
scribed
in
step
f,
check
for defective
com-
ponents
in
the
gate
circuit
of
CR29.
FUNCTION
METER VOLTAGE
1000
100.000
100.0000
LIMIT
Fully
4-55.
HIGH
VOLTAGE POWER
SUPPLY
4-56.
This
test verifies
proper operations of
the high
voltage
power
supply
by
measuring
rectifier
output
voltages
for
all
instrument
voltage
ranges.
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