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 3A 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/343A
controls as follows:
b.
Short circuit the OUTPUT
terminals,
and
set the
voltage dials to 300.000 (300.0000 on the
Model
343A). 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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