HP 416A - Page 77

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 -i mpedance 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.
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Remedies (Cont'd)
(1) If V21 defecti v e ,
replace .
(2) If Vl9 is defec lt ive ,
replace; replace
any defective
capacitor or re -
sistor.
a. Replace V21 if ra t ed
output not obtain e d .
c. Replace RllO or R lll
if either has cha n ged
value.
d. Locate and clear
short.