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 TM 11-6625-542-14-1
(2) Connect negative lead to ground.
6-12.
Test Equipment and Materials Required
(3) Voltage should be -8 +1 volt.
a. Oscilloscope AN/USM-281A.
6-14.
Ripple Voltage Measurements
b. Voltmeter, Electronic AN/USM-98.
The following checks should be performed to check the
c. Variable Transformer CN-16/A.
d. Coaxial cable RG-62A/U, 42 inches long with
ripple level at each of the supply level points. Since
there are no controls for varying the ripple rate, it will be
93-ohm termination.
necessary to service the AN/USM-108A if the
e. Coaxial cable RG-58C/U, 42 inches long with
parameters listed are exceeded.
59-ohm termination.
a. -150 Volts Supply.
f.
Electronic Counter AN/USM-207.
(1)
Connect
oscilloscope
to
variable
transformer.
6-13.
Voltage Measurements
(2) Either remove 1 mc crystal Y201 from
The --150 volts regulated supply can be varied and is
socket, or place a jumper across crystal socket pins
used as a reference voltage for the +225 volts, +350
4 and 6.
volts, -8 volts and --15 volts supply voltages.
(3) Set up oscilloscope as follows:
a.
-150 Volts Supply.
(a) Polarity as required.
(1) Remove cover from AN/USM-108A (para
(b) Vernier sensitivity to 0.2 calibrated.
Horizontal sweep to internal, X5.
(2) Connect variable transformer to correct
(d) Sweep mode to normal.
power source.
(e) Sweep time to 1 millisecond.
(3) Connect AN/USM-108A to variable
(f) Trigger slope to +.
transformer.
(g) Trigger source to internal.
(4) Turn on variable transformer and set at
117 volts.
(4) Connect negative lead of oscilloscope to
(5) Turn on AN/USM-108A and allow 15
ground.
minute warmup.
(5) Connect positive lead to junction of R150
(6) Connect positive lead of voltmeter to
and C144.
junction of R150 and C144.
(6) Ripple should not be greater than 5
(7) Connect negative lead to chassis ground.
millivolts, as viewed on oscilloscope.
b. +225 Volts Supply.
(8) Adjust -150 control (R143) for exactly -
150 volts.
(1) Repeat a (1) through (4) above.
b. +255 Volts Supply.
(2) Connect positive lead of oscilloscope to
(1) Connect positive lead of voltmeter to pin 3
pin 3 of V107.
of V107.
(3) The ripple should not be greater than 30
(2) Connect negative lead to chassis ground.
millivolts, as viewed on oscilloscope.
(3) Voltage should +225 +4.5 volts.
c. +350 Volts Supply.
(1) Repeat a (1) through (4) above.
NOTE
(2) Connect positive lead of oscilloscope to
Since all voltages are a derivative of the -150
pin 6 of V107.
volts supply, it is only necessary to check the
(3) The ripple should not be greater than 30
remaining supply voltages. If the parameters
millivolts, as viewed on oscilloscope.
given are not obtained, it will be necessary to
(4) Reinsert 1 mc crystal Y201, or remove
service the AN/USM-108A.
c. +350 Volts Supply.
jumper wire from crystal socket, pins 4 and 6.
(1) Connect positive lead of voltmeter to pin 6
of V107.
6-15.
1 MC Oscillator Adjustment
(2) Connect negative lead to ground.
a. Connect input of frequency counter to
(3) Voltage should be +350 +7 volts.
AN/USM-108A MARKER OUT connector through
d. -15 Volts Supply.
terminating resistor.
(1) Connect positive lead of voltmeter to pin 3
b.
Set controls of frequency counter to measure
of V393.
a frequency of 1 mc.
(2) Connect negative lead to ground.
c. Adjust C205 for 1 mc output +10 cycles.
(3) Voltage should be --15 1l volt.
6-16.
Divider Circuit Adjustments
e. -8 Volts Supply.
Potentiometers are incorporated in the cathode-coupled
(1) Connect positive lead of voltmeter to
multivibrator circuits to adjust the dividing rate of the
junction of R174 and R176.
stage under test. These are adjusted in the following
manner.
6-23
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