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D
lTt
'°
Symptoms
Instrument NOT
operating;
indic -
ator lamp ON
(cont
'
d)
Poss
ib
le
Cause
HV regulator not
functioning
(cont'
d)
Test Procedure
L
b
.
(cont'd)
(3)
If
there
is
approximately 400
volts at
pin 5 of Vl9, but out-
put cannot be
adjusted to 250
volts
:
c.
Check
voltage
from pin 5 of V2 l to
ground;
should measure
75 volts
±3 volts
.
( 1)
If
V2 l
output not
at
correct
level,
V21
probably is
defective
.
(2)
If
V2 l output is
within
specified
limits, check
Vl9
and
the
cap-
acitors
and
resistors in
the
power
supply circuit.
(Tolerance of
components is shown in Table
of Replaceable Parts.)
2.
Check
the
regulation
circuit as
des
-
cribed
in
Adjustments under Line
Regulation.
If
rated regulation if
not obtained:
a.
Check the output of
voltage reference
tube V2L
Between pin 5 of V21
and
ground
should measure 75
volts ±3
volts.
b.
If
V21
is
delivering specified output
replace V20
,
and
again
check regu-
lator output with line voltage at 103. 5
and 126
.
5
volts.
If
regulation still
not obtained
:
c. Check RHO and Rlll; their resistances
should be
within ±1
Oo/o of
values
shown
in schematic
.
d
.
Check the hum
voltage
(after DC mea-
surements
indicate
regulation
is
ob-
tained)
.
Use a high -impedance VTVM
such as a Hewlett-Packard Model 400A
,
B, C
,
or D.
From pin 3 of Vl9 to
ground
the AC ripple should not be more
than
.
002
volt.
If
AC ripple is more
than
.
002
volt,
check for a cathode-
filament short.
dAOqB puB
6L
1BPdS
SS/92/01
1-t.OOV91.t
Remedies
(Cont'd)
(1)
If
V21 defecti
v
e
,
replace
.
(2)
If
Vl9
is
defec ltive
,
replace;
replace
any
defective
capacitor
or
re
-
sistor.
a.
Replace V21
if
ra
t
ed
output
not
obtaine
d
.
c. Replace RllO
or
R
lll
if either has
cha
n
ged
value.
d. Locate
and
clear
short.
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