TM 11-5805-424-15/NAVELEX 0967-220-9010/TO 31W2-2G-41
and observe that the HP-5233L counter indicates the
(2) Observe oven temperature until a stable reading
frequency of the external timing frequency.
is obtained. If not 750 C proceed to (3) below.
(3) Adjust OVEN TEMP ADJUST control R1 over a
8-3. Demodulator Bias Adjustment
period of 10 minutes to obtain a 75 C reading on the
temperature tester. Lock setting of R1 and apply a drop
performed with an undistorted data input signal applied
of glyptal varnish to shaft.
to the transmit input circuit, and the equipment
(4) Remove probe from oven and replace screw in
connected in a loop-back configuration (para 2-7). Best
top cover.
results are obtained with the MD-674(P)/G operating in
e. Waveform Adjustment. Connect oscilloscope to
the unretimed data mode.
J1 of modem subassembly A 18A2 through A29A2.
b. Adjustment Procedures.
These subassemblies are inserted into the same slot
(1) Connects a data-source (such as the DAC-6A
and use of each is determined by the operating
Pattern Generator) to the front panel ORDER WIRE
frequency. If the subassembly is not inserted into the
SEND jack.
slot because of low operating frequency, connect the
oscilloscope to J1 of subassembly A7. The desired
(2) Connect the 140A oscilloscope between test
waveform is shown in A of figure 8-2. An undesirable
jack J2 on PC assembly A8 (fig. 6-27) and ground.
waveform, that shows a distorted and unstable lagging
(3) Strap, together, terminals 2 and 4 on PC
edge is shown in B. Attempt to correct the distorted
assembly A11 to obtain the unretimed mode of
waveform by adjusting L1. If the distortion cannot be
operation.
adjusted replace the oscillator and oven assembly (para
(4) With power and data signals applied, set the
INPUT SELECT switch (fig. 2-3) to DATA and adjust the
140A oscilloscope for a crossover pattern.
8-2.1. Adjustment of Variable Control Oscillator
(5) Adjust the BIAS ADJUST control until a zero-
(VCO)
bias crossover pattern is observed on the 140A
a. Strap assembly Al for external clock operation
oscilloscope.
by connecting TP4 and TP5 together and terminals 1
8-4. Alarm Adjustments
and 2 together.
a. General. All alarm adjustments are made with
b. Connect the HP-5233L Counter between SEND
transmit data applied and the MD-674(P)/G connected
TERMINAL TIMING OUT #2 terminal 1 of TB2 and
in a loop-back configuration (para 2-7). Both receive
ground terminal 11 of TB2.
and transmit carrier alarm circuits require two
c. Set the BAUD RATE switch to 1200.
adjustments: The threshold adjustment and a delay time
d. With no external timing signal applied and
to activate adjustment. The no-transition alarms require
power applied to the unit, adjust inductor L1 on
only one adjustment.
assembly A1 (fig. 6-2) until the HP-5233L counter
b. Transmit Carrier Alarm Adjustments.
indicates between 1,215 Hz and 1,200 Hz.
(1) Connect the ME-26A/U between test point
e. Connect the external timing signal (150-, 300-,
TP8 (on the control shelf, fig. 2-3) and ground.
600-, or 1,200-Hz) between RECEIVER EXTERNAL
(2) Check the transmit output level by
TIMING INPUT terminal 7 of TB1 and RETURN
connecting the ME-30A/U to BALANCED XMTR
terminal 8 of TB1.
CARRIER OUTPUT terminals 12 and 13 on terminal
NOTE
board TB2 at the rear of the equipment (fig. 1-8).
If the return line is not grounded at
(3) If necessary, adjust the front panel
the signal source, connect a jumper
OUTPUT LEVEL ADJ control for an optimum -7dBm
between RETURN terminal 8 and
output level.
terminal 11 of TB2.
f. Set the BAUD RATE switch to the appropriate
position (as determined by the input signal frequency)
Change 5
8-2
