(1) Connect the oscilloscope between ground
b. Low Output. Recordings which are not up
and the cathode of V15 (pin 7). With
to full density may be traced to:
the PHASE switch operated, the signal
(1) Excessive bias on the cathode, pin 7, of
should appear as indicated on the signal-
V13.
tracing chart. If it does not, trace
(2) Defective transformer T2.
trouble in stage V14.
(3) Low cathode emission in V14.
(2) Check the signal at the other points
(4) Flat-faced stylus or accumulation of
indicated in the signal-tracing chart.
carbon on the stylus. Clean the stylus
c. Phase Magnet. The phase magnet is part of
and rotate it 90.
the cathode circuit of stage V4 when the PHASE
c. Blurred Recording. When the tungsten wire
button is not depressed. Failure of the phase
point which is set in the brass body of the stylus
becomes so worn that a reproduction is blurred
magnet to lock when the PHASE button is not
during the RECORD DIRECT process, change
depressed may be traced to stage V4. Resistor
the stylus needle. Loosen the spring latch (or
R40 is in the cathode circuit of V4 only when the
button is depressed.
screw) that holds the needle; remove the old
needle, and replace it with a new one. Locate the
needle so that the point is in contact with the sur-
a. Signal Tracing. Because of the sensitiveness
face of the direct recording paper mounted on the
drum when the selector switch is in the RECORD
of the output of the photocell circuit, it is not
DIRECT position.
practical to make direct measurements with a
d. Poor Contrast. If the recorded copy lacks
meter or an oscilloscope. It is convenient to use
contrast, and if the transmitted signal has a range
the signal amplifier to feed the oscilloscope, which
of 15 db, the trouble may be traced to low bias
can be connected across the LINE terminals.
voltage on cathode pin 7 of stage V13. This
The signal amplifier and meter circuit first must
voltage may be increased by raising the value of
be checked for satisfactory operation. If the
required measurements on the DB METER and
R67 in Facsimile Transceivers TT-1/TXC-1 and
TT-1A/TXC-1, or by readjusting control R97 in
oscilloscope are not obtained, the circuit should be
Facsimile Transceivers TT-1B/TXC-1 through
traced on a stage-to-stage basis as indicated in the
signal-tracing chart. If the photocell has been
TT-1F/TXC-1. A defective V4 tube also may
be the cause of low bias voltage. When tubes are
subjected to high humidity, it may require replace-
changed, the bias on the cathode of V13 should be
ment. Its dc resistance, measured on an ohm-
checked.
meter when no light is shining on the cell, should
exceed 10 megohms. Be sure to readjust R42
after replacing the photocell with a new one.
a. No Output. To determine whether V16
b. Output Requirement. Set the GAIN control
(884) delivers power to the phase magnet, watch
at 100 and adjust the CONTRAST control for a
the tube when receiving phasing pulses. There
minimum meter reading when the scanning beam
should be a flash within the tube at each pulse
is on the phasing spot. This is the condition for
while phasing, providing a good phasing signal is
positive transmission. The DB METER should
being received. On Facsimile Transceivers TT-1/
indicate +2 or +3 db when the scanning beam is
TXC-1 and TT-1A/TXC-1, a quick test with no
on the raised portion of the phasing ring. The
received signal can be made by depressing the
equipment will operate satisfactorily even though
PHASE button and giving the START button
the reading is not above 0 db. It is desirable,
a short, quick push. A flash within the thyratron
but not necessary, to have the 2- or 3-db margin.
should occur each time the START button is
If the output level is not proper, check the align-
depressed.
ment of the optical system; check amplifier stages
b. Signal Tracing. Connect the transceiver
V10, V11, and V12; then check the voltage across
under test to a second transceiver for the purpose
resistors R41, R42, and R43. This should be
of obtaining a phasing signal. Set the CON-
between .4 and .6 volt.
TRAST control of the sending transceiver to pro-
c. Low Contrast. Insufficient contrast when bal-
duce a 6- to 8-db phasing pulse with the CON-
anced on black or white generally can be corrected
TRAST control in the range for negative trans-
by the adjustment of resistor R42. Excessive
missions.
voltage from the fork unit reduces the contrast
