TM 11-6125-261-30
NOTE
CAUTION
Input current should reach approximately 10
The overcurrent limit foldback will act within
amperes when the input voltage reaches +15 to
20 seconds or less. Make adjustments and
+ 16 V dc. Input current should then drop to a
readings quickly. Set S1 and S6 to off and
final value of approximately 4 to 6 amperes at
allow the inverter to cool at no load at least one
+28 V dc.
minute for every 15 seconds of overload
operation. The overload operations may then
(4) with input set at +28 V dc, the output indications
be repeated until this adjustment procedure is
on the true RMS voltmeter shall be exactly 115.5 V ac. If it
completed.
is not, adjust potentiometer A22R109 for 115.5 V ac on the
NOTE
NOTE
load share between phases. Adjusting one
Brush on protective coating to reseal poten-
phase will change the other two phases.
tiometer adjustment screws after this adjust-
e. Set S1 to load and S6 to overload. Adjust the
ment procedure has been completed.
(5) If the output cannot be set to 115.5 V ac, turn off
per phase. The output voltage should be 65 V ac 5 V ac.
the equipment and troubleshoot inverter as described in
f. If
the output voltage is
too high, decrease the resistance
of A22R125 for phase A, A21R121 for phase B, or A21R21
b. Phase B. Output Voltage.
for phase C as required. If the output voltage is too low,
(1) Set test fixture switches as follows: S1 -- No load;
increase the resistance. Readjust the load for the changed
S2-- Phase B; S3-- PhaseB;S4--+1.0; S5--Off; S6 --
voltage.
Off.
g. When correct operation if achieved, set S1 and S6 to
(2) Repeat steps 3 to 5 of phase A adjustment
off and set Vin to 0.0 volts. Disconnect the inverter and
procedure, except if adjustment is necessary adjust A21R1.
install the correct value resistors. Verify that the inverter
c. Phase C Output Voltage.
now functions properly.
.
(1) Set test fixture switches as follows: S1 -- No load;
3-10. Output Distortion Adjustment
S2 -- WYE; S3-- Phase C; S4-- + 1.0; S5 -- Off; S6--
NOTE
Off.
(2) Repeat Steps 3 to 5 of phase A adjustment
This adjustment is factory set and should not
procedure, except if adjustment is necessary adjust
require readjustment unless transformer was
A21R101.
not replaced, perform all other adjustment
procedures before making this adjustment.
3-9. Overcurrent Limit Adjustment
a. To adjust the output distortion, proceed as follows:
a. Use test procedure 3 of
table 3-9 to
check for proper
operation.
NOTE
NOTE
If the inverter fails to meet any voltage, current,
This adjustment is factory set and should not
course of the following test, troubleshoot the
require readjustment unless the interstage
transformer (A2T2, T3 or T4) and/or the
defective circuits in accordance with the
applicable paragraph. After repairs have been
current sense resistor (A2R25, R26and R27) is
made, repeat the entire output distortion check.
changed.
(1) The output distortion check shall be performed
b. With the inverter off, disconnect one end of A22R125,
with the inverter completely assembled to provide adequate
A21R21 and A21R121. Jumper in a resistor decade box.
cooling air. Note that if the output distortion check does
Set the decade box to the same value as the disconnected
not meet specifications, the inverter will have to be
resistor. (In serial numbers 8439-1310C and up, it is not nec-
essary to use the decade box and disconnect and replace re-
disassembled to adjust the affected circuits.
sistors, because the fixed resistors were changed to variable
(2) Connect the inverter to the test equipment as
resistors.)
NOTE
CAUTION
Due to the differences between individual test
Isolate the true RMS voltmeter, the distortion
stations, the following setting is not always the
same. The approximate setting will have to be
from earth ground to avoid inadvertent shorts
determined by trial and error.
in the inverter output.
d. Preset the load box to the approximate setting, which
(3) If distortion exceeds that specified in table 3-10,
will give a load of 4.36 amps per phase at 65 V ac.
select a new capacitance value which gives best overall
Change 2
3-21