HP 400D Operating And Servicing Manual page 24

Sect.W
Page
8
Table
4-2.
Trouble Shooting
Chart
SYMPTOM
POSSIBLE CAUSE
AND/OR
REMEDY
Instrument dead, indicator lamp
does
not
light.
Fuse
Blown
-
replace. If fuse
blows
again,
check
for
a
short circuit or
defective tube
or
component
in
power-supply and/or heater circuits.
Off-on switch defective.
Line cord
defective.
Instrument dead, indicator lamp
glows,
meter
does not indicate.
No output
from regulated power
supply. Refer
to
paragraph 4-9.
Tubes
Vl,
V2, V3, V4,
and/or Vb defective.
Defective
component
in amplifier.
Defective CR1 and/or CR2 diode, C34 capacitor, or
meter movement.
Check
instrument calibration
after repair.
Residual
meter reading
erratic
and
higher
than
2
divisions
on
the .001-volt scale.
(Input
must
be
well
shielded.
)
This is usually
accompanied
by
erratic
meter indica-
tions.
See
Meter Indication
Erratic.
Residual
meter
reading steady and
higher
than
2
divisions
on
tie l-volt
scale.
Trouble in power supply
(see
paragraph 4-9)
YL, V2, V3, V4,
and/or Vb defective.
Defective
component
in amplifier.
Noisy R
23.
Capacitor
CG
is
formed
by
wires
cormecting
to
adjacent
tie
lug
terminals.
If
the heater leads
for
Vl
are
dressed
so
that they pass
between
these
terminals,
hum
is
introduced.
Meter indication
is
equally
erratic
on
all
ranges.
Trouble in power supply (see paragraph 4-9).
Tubes
V2, V3, Y4,
and/or V5 defective.
Crystal
diode
CRl
and/or
CR2
defective.
Capacitor C2 may be shorted
or
Lealry.
Noisy
R23.
Meter indication more
on one range then
on other ranges.
Leaky 0.051
pf
coupling capacitor
in
range switch.
Replace defective Unit.
Meter pointer'tbeats"
when power line
frequency (usually 60 cps) or
a
harmonic
thereof
is
applied
to INPUT.
Trouble in power supply (see paragraph 4-9).
Heater-cathode leakage
in
V1, V2, V3, V4 or
V5.
Replace one
tube
at a time.
Readjust heater d-c
voltage
after final
tube selections have been made.
Recalibrate instrument (paragraph 4-7d).
Open
bypass
or
decoupling
capacitor anywhere in in-
strument.
e)
U