HP 416A - Page 84

!
O'
O'
i
Instrument oper-
ating but meter
indicates steadily
toward the low
stop (cont ' d).
Instability in meter
indication when
measuring small re -
flect i ons (approxi-
mately 3% or less) .
416A004-l 10/26/55 Seri~'i 79 a' nd above
Trouble in the
reflected channel
(cont ' d) .
Hum voltage
Noise
( 1) If the required voltages cannot
be ohtained , Filter 2 probably
is defective .
(2) If v oltages at C27 and C41 are
correct , localize trouble as in -
dicated in steps 8 and 9 above .
With a h i gh - impedance vacuum tube volt~
meter (Hewlett - Packard Model 400A , B • C
or D). measure the AC ripple voltage.
From pin 3 of Vl9 to g round the AC ripple
should be not more than • 002 volt . If AC
ripple measures more than . 002 volt :
a. Check regulat i on (see step 2 of
"HV regulator notfunctioning" ,
above) .
b .
Inspect ground connections (at
lugs on rear of INCIDENT /REFER-
ENCE and REFLECTED/PROBE
connectors).
Check the following possible sources of
circuit noise :
a. Tubes (V3 and V4)
b. All plate res i stors (check resistance
and that soldered bond is good).
c. Check circuit for any loose connection.
d. Check that ground connections (at
lugs on rear of input connectors) are
firm and free from corrosion.
e. Noise pickup from external test equip-
ment tied to the Model 416A by input
cables or ground connections.
a. If regulation not
obtained, clear
trouble.
b. Resolder , if
necessary .