residual dc flowing in the synchronous motor
range. The voltage can be reduced by shunting
coils. Failure of the signal amplifier circuit to
the output of the fork unit with a 2,000-ohm
operate properly may be caused by a burned-out
resistor. Sometimes, the correction can be made
exciter lamp or a poor switch contact. The dis-
by increasing the value of R49 (except in Facsim-
appearance of the characteristic 1,800-cycle tone
ile Transceivers TT-1D/TXC-1, TT-1E/TXC-1,
in the synchronous motor indicates proper opera-
and TT-1F/TXC-1). The exact amount of this
increase can be determined by experiment. Low
tion of the grounding circuit.
contrast also may be caused by lack of light from
the exciter lamp (par. 102).
a. Requirements. The B+ voltage regulator
must deliver voltage that does not vary more than
a. Low Output. The signal amplifier circuit,
2 volts when operating conditions change. The
with the selector switch in the TRANSMIT posi-
voltage may be anywhere between 240 and 255
tion, is a modification of the signal amplifier circuit
volts dc. The measurements may be made at the
with the selector switch in the RECORD PHOTO
bottom end of resistor R88 or R89 on the regulator
position. In practice, it is generally found that
panel terminal strip, or on pins 3 and 6 of stage
if the signal amplifier operates correctly in the
V16 in Facsimile Transceivers TT-1/TXC-1 and
TT-1A/TXC-1. This voltage is measured by
RECORD PHOTO position, it performs properly
with the switch in the TRANSMIT position. A
RB+ meter M3 in Facsimile Transceivers TT-
quick check to determine whether the input circuit
1B/TXC-1 through TT-1F/TXC-1.
has been properly switched to the photocell circuit
b. Effects of Poor Operation. If the regulated
is to place a screw driver under the extension of
voltage is too high, the fork frequency deviates
the photocell shield pan. Do not let the blade
from 1,800 cycles and causes a noticeable drift in
the recorded copy. A low voltage also will result
touch the grid connection or the pan. If the
amplifier is performing properly, it breaks into
in a drift and permit the amplifiers to overload on
a high signal level. The overloading shows up as
oscillation. In most cases, if the input circuit is
open, oscillations will be present and will be indi-
flattened high lights when transmitting for nega-
cated by continuous flickering of the DB METER.
tive reception, or flattened shadows when trans-
b. Signal Compression. Connect the oscillo-
mitting for positive reception. A flickering volt-
scope and DB METER across the LINE termi-
age regulator may produce level changes and may
nals. The waveform should be sinusoidal be-
oscillate when the line voltage is low. The
tween the balance point and +2 db. If the wave-
oscillations will show up in the recorded copy.
c. Tracing trouble. When trouble is suspected
form tends to compress before reaching +2 db,
trace through the circuit to localize the trouble.
in the regulator unit, check the output voltage
The flattening or compression of the signal maybe
with the line voltage varying between 100 and 130
caused by low plate voltage, low cathode bias
volts. The ac input frequency may be between 50
and 65 cycles. Watch the test voltmeter for
voltage, low screen voltage, or defective tubes.
several minutes when level change trouble is being
traced. If the voltage takes a jump when the line
voltage is within a few volts of 110, there is
With the selector switch of Facsimile Trans-
ceiver TT-1/TXC-1 in the STANDBY position,
danger of the regulator breaking into oscillation
at low line voltages. If it is important to operate
the fork oscillator signal to the motor amplifier is
at an exact line voltage, it will be necessary to use
effectively short-circuited to ground through pin
an accurately calibrated voltmeter to measure the
9 of the Jones plug and the exciter lamp and its
line voltage. Most rectifier-type voltmeters can
circuit. (In all other facsimile transceivers, the
STANDBY-MON-TALK switch (S5) also must
be depended on for an accuracy of 5 percent at
be at STANDBY.) In Facsimile Transceiver
temperatures between 65 and 100 F. Above
TT-1C/TXC-1, the B+ circuit to the motor is
and below these temperatures, the accurary is
generally poor. If it is found that the regulated
opened when selector switch S1 and STANDBY-
B+ voltage is not within the correct range, check
MON-TALK switch S5 are both at STANDBY.
the voltage across regulator lamp V25 (5651).
By short-circuiting the 1,800-cycle signal to the
This can be done by measuring the voltage
motor amplifier, the power to the synchronous
between cathode pin 7 of tube V9 (7L7) and
motor is practically cut off. There is only a small
