DIRECT SUPPORT MAINTENANCE INSTRUCTIONS
Section I. GENERAL
coded to the test points (Al through A20) shown on the
The maintenance allocation chart for the in-
verter is located in TM 11-1520-236-20.
designator of the component or terminal where the
measurement is taken.
3-1. Voltage and Resistance Measurements
3-2. Wire List
a. Table 3-1 shows the voltage and resistance measure-
ments that can be expected in the inverter. Voltages were
a. The inverter uses two wire harnesses and one wire
measured with no load on the output.
assembly. in addition the A1 module uses nine short
jumpers of No. 18 bus wire and 18 short jumpers of No. 16
black insulated wire.
Relatively low voltage but high current is
b. The 277B2023 wire hamess is composed of No. 16, 20,
present in the inverter.
22 and 24 gauge wire for control signals. The 277B3300 wire
harness is composed of No. 16 guage wire for high current
b. Resistance measurements are shown in the forward
signal connections to the main transformer. The 277C1340
and back mode. The resistance on the top indicates the
wire assembly is composed of No. 14 gauge red insulted wire
forward resistance and the value on the bottom indicates
for the M28 V dc power bus. All insulted wire is in accord-
ance with MIL-W-16878/1 or MIL-W-16878/4A. The crimp
c. Table 3-2
is across reference between the components
lugs are AMP Products Corp., Valley Forge, PA. 19482,
for all three phases that have the same function.
FSCM00779 or equivalent.
d. Figure 3-1, sheets
all the significant
c. Table 3-3 contains
a to-from wire
list for the inverter.
waveforms required for maintenance. Each waveform is
Table 3-1. Voltage end Resistance Measurements
A. Voltage measurements
+28.0 V dc
1. Input voltage
Adjust to 115.5 V ac f V sc 400 Hz No Load.
2. Output voltage
Voltages are references to ground.
3. Voltage listing
The A-number in the voltage columns indicate the test point reference number of the waveform. Refer to figure 3-1.
. Resistance measurements.
1. Unit OFF and disconrectcd from the +28 V dc source
3. Remove associated Z elements indicated by *.
5. The transistor type is noted below the referenced designation. All transistors and diodes are silicon types
6. This table shows the transistors, for OA only. Refer to table 3-2 for equivalent B and C transistors.
7. Top number in Resistance column indicates forward resistance, bottom, backwards resistance.