HP 400D Operating And Servicing Manual page 29

TABLE 4-2.
Symptom
Meter. indication is equally erratic on all ranges.
Meter indication more on one
ranges.
Meter painter "beats" when power line frequency
60
(usually cps) or a harmonic thereof is ap-
plied to INPUT.
Repeated adjustment to increase amplifier gain
needed to maintain calibration.
Meter pointer strikes peg sharply when switching
ranges, particularly when switching from
to I-volt range with no input.
Delayed secondary switching transient particularly
when switching from
with no input.
Microphonics
(Mechanical shock causes excessive fluctuation
of voltmeter reading.)
TROUBLE SHOOTING CHART (CONT'D)
range than on other
O.
the
0 . 3- to the I-volt range
Possible Cause and/or Remedy
Trouble in power supply (see paragraph 4-9).
Tubes V2, V3, V4 and/or
cm
Crystal diode
Capacitor C2 may be shorted or leaky.
NOisy R23.
Leaky 0.051 Ilf coupling capacitor in range switch.
Replace defective unit.
Trouble in power supply (see paragraph 4-9).
Heater-cathode leakage in VI, V2, V3, V4 or V5.
Replace one tube at a time.
dc voltage after final tube selections have been
made. Recalibrate instrument (paragraph 4-7).
Open bypass or decoupling capacitor anywhere in
instrument.
Trouble in power
VI,
Tubes V2, V3, V4 and/or V5 defective.
Crystal diodes CRI and/or CR2 defective.
Capacitors C32, C33, and/or C34 defective.
Tubes VI, V2, and/or
3- tube defects.
defective.
The only disadvantage of this is a slight increase
of instrument recovery time when switching
ranges. Most probably caused by a gassy tube
for VI, V2, and/or VS.
o r V4.
A similar symptom may exist between any two ranges
when any of C7 through C12 capacitors are
leaky.
With DB VOLTS switch on I-volt range, apply a
to
I-volt (400 1000 cps) signal to INPtrr.
tap lower right corner of meter case.
p01nter pins Sharply against right hand stop,
tubes VI andlor V2 are microphonic.
N
Sect.
V5 defective.
and/or CR2 defective.
Readjust heater
supply (sp.e
paragraph
4_9).
V5 are the most probable
However, V3 and/or V4 maybe
May also be V 3 andl
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Llghtly
H
meter