TM 11-6625-444-14-1
and set the POWER switch to ON. Depress the
or anode of CR14.
VAC pushbutton.
n. With no input voltage applied to the INPUT
TP4 and common (shield).
terminals, the oscilloscope should indicate within
d. Short HI to LO INPUT terminals. The in-
100 millivolts dc of zero. With a full range voltage
dication should be within 100 millivolts of zero. If
at 500 Hz applied to the INPUT terminals, the
indication is incorrect , proceed to f below;
oscilloscope should display a clean halfwave rec-
otherwise proceed to the next step.
tified sinewave of 1.4 volts peak. If the indication
e. Remove the input terminal short and apply a
is incorrect, troubleshoot the balance amplifier
full range voltage to the voltmeter input at 500
circuit. R e f e r to table 7-2 and perform the
Hz. `The differential voltmeter should indicate
measurements for U4, Q9, and Q10.
between 9.95 to 10.05 volts when connected
o. Move the oscilloscope probe to test point
between TP4 and common (shield). If indication is
TP1.
incorrect, proceed to j below; otherwise proceed to
p. With no voltage applied to the INPUT ter-
the next step.
minals, the oscilloscope should indicate within 100
f. Remove any input voltage or short at the
millivolts of zero. With a full range voltage at 500
input terminals. Short TP1 to common (shield). If
H z applied to the INPUT terminals, the
the indication changes to within 100 millivolts of
oscilloscope should display approximately -- 1.2
zero, proceed to j below; otherwise proceed to the
volts dc with a clean ac scallop superimposed. If
next step.
the display is incorrect, troubleshoot the squaring
g. Short test points TP1 and TP2 to test point
amplifier circuit. Refer to table 7-2 and perform the
TP5.
measurements for U5, TP1 and Q11.
7-17. Matched Set Replacement
test point TP4. The indication should be within
The ac converter contains a set of factory selected
100 microvolts of zero and be adjustable with R66
components. This set consists of Q8, Q12, R48,
(integrator amplifier zero). If indication is in-
R79, and R80. These components are selected for
correct, troubleshoot the integrator amplifier
overall ac converter temperature coefficient and
circuit. Refer to table 7-1 and perform the
linearity. In case of replacement, the total set
measurements for U7, U5, Q14, Q15, and TP4.
must be installed. Depending on the matched set
i. Remove short at test point TP2 (maintain
received for replacement, some, or none, of the
short between test point TP1 and common).
three resistors may be included. In positions where
Connect the high lead of the differential voltmeter
a resistor is not required, install a piece of bus
to TP2. The indication should be within 200
wire.
millivolts of zero and be adjustable with R55
(square root amplifier zero adjust). If the in-
a. Adjustment of the ac converter is not
dication is incorrect, troubleshoot the square root
authorized at the General Support level. If the PL-
amplifier circuit. Refer to table 7-1 and perform the
1370/GSM-64B fails to meet the parameters
measurements for U6 and TP5.
required in b below, the item must be sent for
j. Remove any input voltage and disconnect the
differential voltmeter and all shorts.
b. After repairs have been made to the ac
k. Connect the oscilloscope with low capacitance
converter, install the item into a working volt-
probe between the threaded body of C11 (10 volts
meter. Set the voltmeter for vac measurement with
50 kHz adjust) and common.
ac input coupling. Connect the TS-682/GSM - 1 to
l. With no voltage applied to the INPUT ter-
the INPUT terminals of the voltmeter. Apply the
minals the oscilloscope should display zero volt.
input signals listed in table 7-1, set the appropriate
With a full range voltage at 500 Hz applied to the
range and observe the output indication on the
INPUT terminals, the oscilloscope should display a
voltmeter. The output should be between the
clean sinewave of 2.8 volts peak-to-peak. If the
values listed in the voltmeter indication column.
indication is incorrect, troubleshoot the range
amplifier circuit. Refer to table 7-1 and perform the
measurements for U3, TP3, and Q5.
Change 1 7-9
