input terminals of the oscilloscope. Note the
600-volt capacitors may be used, but should be
deflection. Without changing the setting of the
changed when the correct rated capacitor is
vertical gain control on the oscilloscope, discon-
available.
nect it from the filament supply and connect it
d. Power Cable. If the power cable or Jones
across the exciter lamp supply. The exciter lamp
plug is damaged, a replacement may be made
voltage should cause approximately the same
with a complete cable and plug assembly available
peak deflection on the oscilloscope (90 percent is
at signal depots. If it is only nicked or scuffed
sufficient). With the exciter lamp voltage prop-
(not beyond insulation) it may be repaired with
erly set in this manner, it may be measured on a
rubber tape.
conventional ac voltmeter and the voltmeter
reading recorded as a standard against which
122. Hum Balance Control R107
future checks may be made. If the exciter lamp
Facsimile Transceiver TT-1F/TXC-1 has a
is lighted, and the voltage across it is slightly low,
hum balance control, R107. It is connected
check output tubes V19 and V20. If the tubes
across the filaments of the tubes and is adjusted
are in good condition, readjust control R15. If
for minimum hum. This control is set at the
correct voltage cannot be obtained, check the
factory. If readjustment of the control is neces-
regulator lamp with a vacuum-tube voltmeter,
sary, proceed as follows: With the selector switch
Set the meter on the 250-volt scale and connect
set at RECORD PHOTO, connect an oscilloscope
across the regulator lamp (V23) terminals. The
between pin 3 of V14 and ground. Turn the set
voltage should be between 82 and 92 volts dc.
ON and set the GAIN control at 100 with no
If the reading is out of this range, replace the tube.
signal input. Set the oscilloscope for a low
If the regulator lamp is in good condition, check
sweep rate and observe the 60-cycle hum pips as
tube V21. If the output voltage is below 5 volts ac,
control R107 is varied. When the hum pips
check tubes V19 and V20. If the tubes are in good
are at a minimum, R107 is set properly. An ac
condition, check the signal voltage on the grids
voltmeter may be used in place of the oscilloscope.
(pin 6) of V19 and V20. If the grid voltage is
Connect the voltmeter between one side of the
normal or above normal, transformer T15 is
filament and ground. Adjust R107 until a read-
defective. See the signal-tracing chart (fig. 81).
ing of 3 volts is obtained. Satisfactory record-
This transformer must be replaced with an exact
ing can be made at this level.
equivalent. The exciter lamp may be checked
by connecting it to a 6-volt battery.
Caution: If the exciter lamp is removed, a re-
placement must be made before the power is turned
a. Condition. Set the selector switch to the
on. Operation without an exciter lamp may
SET RANGE or TRANSMIT position. Turn
cause damage to transformer T15.
the power on. Measure the exciter lamp voltage
at secondary No. 2 on transformer T15 (fig. 158).
may be replaced with any close equivalent which
A regular ac voltmeter will not give an accurate
fits into the available space. Transformer T14
reading of this voltage, which is not a sine wave.
may be replaced with a conventional driver
First calibrate an oscilloscope to serve as a volt-
transformer having a ratio ranging from 1:1 to
meter by applying 6.5 volts from one of the fila-
ment windings of the facsimile set to the vertical
1: between primary and one-half of the secondary.
Section IV. EMERGENCY REPAIRS AND OPERATION
124. General
Emergency conditions of operation and repair
a. Resistors. All -watt resistore may be
may require deviation from normal procedures
replaced with - or 1-watt resistors. When mak-
and standards. This section covers information
ing a replacement, select a resistor having a value
required for operation under emergency conditions
as near as possible to the value specified.
and for making emergency repairs which will keep
b. Capacitors. Except for capacitors C28 and
the equipment in operation until full repairs can
C29 in the motor circuit and capacitors in the
be made (figs. 128 through 140, and 145 through
195).
unsealed fork oscillator unit, the capacitance
