Sect.
IV
Page 10
If
the regulator output is within these limits, the
power supply probably is functioning properly, and
the remainder of the circuit should
be
tested.
Apply a signal at
lli'FUT,
and check the level of the
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
of
D.
3 volt at 400
CYCles, may be found in Figure 4-3, a servicing
block diagram.
2) When trouble has been localized to a particular
section, it is recommended that tube substitution be
tried before any other tests are made.
If
tubes
known to be good do not clear the trouble, voltage
reSistance measurements should be made. Typical
voltage and resistance values may be found on Tube
Socket Voltage-Resistance Diagram, Figure 4-4.
For the circuitry in each section reference may be
made on
the
schematic dia.gra.m. The servicing block
diagram (Figure 4-3) shows the signal path in heavy
line and directional arrows, Feedtack plths are
shown
by means of directional arrows, but in lighter line.
Localization by
de
voltage analysis is discussed in
paragraph 4-10.
TABLE 4-2. TROUBLE SHOOTING CHART
Symptom
PosRible Cause and/or Remedy
Jnstrument dead,
indicator lamp does not light,
Fuse blown - replace.
If
fuse blows again, check
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.
Instrument dead,
indicator lamp glows, meter does
No output from regulated power supply.
Refer to
not indicate.
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,
Residual meter reading e rratic and higher than
This is usually accompanied by erratic meter in-
2-1/2 divisions on the . 001- volt scale.
(Input
dications.
See Meter Indication Erratic.
must be well shielde d, )
Residual meter reading steady and
higher
than 2-1/2
Trouble in power supply (s-o!e paragraph 4-9).
divisions on
the I-volt
scale.
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 tie lug terminals.
H
the heater leads for
VI are dressed
so
that they pass between these
terminals, hum is introduced.
