HP 400D Operating And Servicing Manual page 28

IV
Sect. Page 10
If
the regulator output is within these limits, the
power supply probably is functioning properly, and
the remainder of the circuit should
lli'FUT,
Apply a signal a t
signal voltage at the input and output of each of the
sections shown in Figure 4-3, except the levels at
1st amplifier V2. (The low level of signal applied
to the grid of V2, together with the large amount
of negative feedback applied to its cathode, make any
signal-voltage measurements at V2 impraCtical.)
Typical signal voltages at the input and output of
each section, for an input signal
CYCles, may be found in Figure 4-3, a servicing
block diagram.
Symptom
Jnstrument dead, indicator lamp does not light,
Instrument dead,
indicator lamp glows, meter does
not indicate.
Residual meter reading e rratic and higher than
2-1/2 divisions on the . 001- volt scale .
must be well shielde d, )
Residual meter reading steady and
the I-volt
divisions on
be
tested.
and check the level of the
of
3 volt at 400
D.
TABLE 4-2. TROUBLE SHOOTING CHART
(Input
higher than 2-1/2
scale.
2) When trouble has been localized to a particular
section, it is recommended that tube substitution be
tried before any other tests are made.
known to be good do not clear the trouble, voltage­
reSistance measurements should be made.
voltage and resistance values may be found on Tube
Socket Voltage-Re sistance Diagram, Figure 4-4.
For the circuitry in each section reference may be
the
made on schematic dia.gra.m .
diagram (Figure 4-3) shows the signal path in heavy
line and directional arrows, Feedtack plths are
by means of directional arrows, but in lighter line.
de
Localization by voltage analysis is discussed in
paragraph 4-10.
PosRible Cause and/or Remedy
Fuse blown - replace.
for a short circuit Or defective tube or com-
ponent in power supply and/or heate r circuits.
Off-on switch defective.
Line cord defective.
No output from regulated power supply.
pa.ragraph 4-9,
Tubes VI, V2, V3, V4 and/or V5 defective .
Defective component in ampliiier.
Defective CRI and/or CR2 diode, C34 capacitor, or
meter movement. Chec k instrument calibration
after repair,
This is usually accompanied by erratic meter in-
dications. See Meter Indication Erratic.
Trouble in power supply (s-o!e paragraph 4-9).
VI, V2, V3,
V4, and/or V5 defective.
Defective component in amplifier.
NOisy R23.
Check mechanical zero.
Capacitor C6 is formed by wires connecting to ad-
jacent ti e lug terminals.
so
VI are dressed that they pass between these
terminals, hum is introduced.
If
tubes
Typical
The servicing b lock
shown
If
fuse blows again, check
Refer to
H
the heater leads for