TM 11-6720-242-35
and perform the following procedures to check its
(6) Connect the voltmeter across pins 1E and 1F
suitability. The replacements must be repeated until the
(neither pin grounded) and increase the voltage input
given test results are obtained. Resistors are 1/8 watt,
across pins 2K and 1A to obtain a reading of 8 0.5
have a tolerance of 1 percent, and have the following
volts, rms. The voltage change across pins 2K and 1A,
values:
over that recorded in step (4) shall be + 0.075 0.03
vdc.
14.3K
(7) With the voltmeter connected across pins 1E and
14.7K
1F, increase the voltage input across pins 2K and 1A
15.4K
until a reading of 12 volts rms is obtained.
15.8K
(8) Decrease the voltage input across pins 2K and 1A to
below the value recorded in step (4) to obtain a
(1) Connect a jumper wire between pins 2a and 1Z.
voltmeter reading of 8+0.5 volts, rms. The voltage
(2) Adjust the power supply for an input of 121vdc
change across pins 2K and 1A shall be +0.075 0.03
across pins 2a and 2A. Connect the voltmeter across
vdc below the value recorded in step (4).
pins 2u and 1A and check for a reading of 11+2vdc, as
(9) Decrease the voltage input across pins 2K and 1A to
an indication that the mode relay K3 is in the autocycle
obtain a voltmeter reading across pins 1E and IF of 12
position (energized).
volts, rms.
(3) Decrease the voltage at pin 2a until the 11vdc
e. Checking Motor Speed. With the motor free
disappears from pin 2U and appears at pin 2P. This
to rotate, connect the voltmeter across pins 1E and 1F.
voltage at pin 2a must be between +7.9 and +8.7 vdc. If
Adjust the input voltage across pins 2K and 1A to obtain
the reading is not within this range, replace R22 with a
a meter reading of 12 volts rms. Use a strobotac to
resistor of different value from among those listed until
check that the motor shaft is rotating at a speed of 3000
the proper voltage is achieved.
rpm.
(4) Decrease the voltage at pin 2a to +6.0 0.5vdc.
f. Testing Scaling Accuracy.
The voltage at pin 1W shall be +11 2vdc.
(1) Adjust the voltage supply connected to pin IT for an
(5) Increase the input voltage until + 11vdc disappears
input of -6.0+0.006 vdc.
from pin 2P- and appears at pin 2U. The value of the
(2) Connect the voltmeter to pin 1P. Adjust the power
input voltage at pin 2a must be between +8.9 and +
supply connected to pin 2N to obtain a reading of + 6.0
10.2vdc.
+ 0.006 vdc.
(6) Compare the difference in the present input voltage
(3) Connect the voltmeter to pin 2L and pin 1A and
to pin 2a with that recorded in step (4). The difference
adjust test potentiometer R. to obtain a meter reading
shall be greater than 0.8 volt but less than 2.5vdc.
of -3.0+0.003 vdc.
(7) Remove the jumper wire between pins 2a and 1Z
(4) Connect the voltmeter across pins 1E and IF (neither
when the test has been completed.
pin grounded) and adjust the voltage input to pin 2K to
obtain a null voltage (minimum) meter reading.
are selected by test from among the following listed
4-8. Testing Control Board Assembly
values if the tinting between intervalometer pulses has
been found incorrect. Resistors R34 and R35 must be
changed until the correct value is determined by
Insert the control board assembly into the connector of
performing the following procedures. Resistors are 1/8
the special test fixture, shown in figure 4-3.
watt and have a tolerance of 1 percent and have the
NOTE
following values:
When the designated value or
R34
R35
condition of a test is not obtained,
remove the control board assembly
22.1K
12.4K
from the test fixture and trace the
23.2K
13.0K
malfunctioning circuit in figure 6-14
24.3K
13.7K
to isolate the faulty part or assembly
25.5K
14.0K
for replacement.
26.7K
14.7K
28.0K
15.4K
a. Checking Mode Switchover Resistor R22. The
29.4K
proper value of resistor R22 is selected by test from
among the following listed values. If the switchover
from autocycle mode has not been consistent with the
v/h input, replace R22 with a resistor of different value
4-12
