(2) If the motor current is between 40 and
70 ma for 60-rpm operation, any one or
all of tubes V4, V5, and V6 may be,
weak.
(3) If the current is less than 40 ma, the
trouble is probably a defective com-
ponent.
(4) If motor current is excessively high, the
motor may be short-circuited.
(5) If the troubles are not located by the
above checks, follow the signal-tracing
charts.
straight uniform skew or a drift, the frequency
of either the transmitter or the receiver fork is
off standard.
underlap.
(1) The set under question can be tested by
transmitter. Check the clutch tension as outlined
using it to record radio signals from sta-
in paragraph 106. If the tension is correct, take
tion WWV, Washington, D. C. The
the necessary measures to eliminate the bind in
signals include 1 pulse each second.
the defective drum or lead screw (pars. 107
If the fork is adjusted properly, a
and 108).
straight-line pattern parallel to the drum
clamp will he recorded.
(2) If a signal is available from a facsimile
a. General. The output circuit of the motor
transceiver having a fork known to be
amplifier includes choke T6, capacitors C28, C29,
in perfect adjustment, a comparison can
and C30, as well as the synchronous motor wind-
be made with the set under test, and
ing.
adjustments can be made. Feed the
Caution: The high voltage at the terminals of
accurate signal into the transceiver under
the synchronous motor, choke T6, and capacitors
test through the 6-volt connection of
C28, C29, and C30 may be dangerous to life.
the UC feed coil. Set the selector
Shut off the power when connecting a meter or an
switch at RECORD PHOTO. Adjust
oscilloscope to these components. Do not touch
the GAIN control for a meter reading
the meter or the oscilloscope when the power is on.
of 2 db. Move the feed coil close to
In Facsimile Transceiver TT-1A/TXC-1, do not
the synchronous motor. The indention
replace the motor fuse without discharging capaci-
on the DB METER will rise and fall.
tor C31, or the fuse may blow. In Facsimile
The amount to rise and fall will depend
Transceivers TT-1B/TXC-1 through TT-1F/
on the position of the feed coil with re-
TXC-1, wait (a few seconds) for capacitor C31
spect to the motor. The rate of rise and
to discharge through resistor R95 before attempt-
fall will indicate the off-frequency con-
ing to replace the motor fuse.
dition of the fork. Adjust control R25
b. Low Output.
In Facsimile Transceivers
in unsealed units, or R304 in sealed units
TT-1B/TXC-1 through TT-1E/TXC-1, motor
until the rate of rise and fall drops to less
current is read directly on MOTOR CURRENT
than one full swing in 2 minutes.
meter M2. In Facsimile Transceivers TT-1D/
b. Caues of Frequency Drift.
TXC-1, TT-1E/TXC-1, and TT-1F/TXC-1, M2
(1) Condensation of moisture on the unsealed
should indicate 40 to 60 ma for 30-rpm operation,
tuning fork will cause a frequency drift
and 55 to 80 ma for 60-rpm operation.
until the moisture evaporates.
(1) If the input to the motor amplifier is low,
(2) Rusting of the unsealed tuning fork will
the exciter lamp will not light to full
brilliancy.
affect the frequency.
140
