Section III. TROUBLESHOOTING
To avoid electrical shock, be extremely careful
formed to isolate the faulty components and to identify the
when making required measurements and
cause of the failure. It will "be necessary to remove
protective coating from leads to take readings.
b. Troubleshooting will be performed with the inverter
disassembled as necessary. Connect the test fixture shown
a. Since there are no external controls or indicators on
the inverter, performance indications may be measured
c. Once the cause of the malfunction has been determined
with the inverter disassembled on the test bench. While
and corrected, ensure that the defective component was the
voltages in the inverter are relatively low (that is. M28 V dc
cause of the problem and not the result of another defective
and 115 V ac). current levels are high (up to 45 amperes in
normal operation. and much higher in short circuit
d. Table 3-6 provides instructions for troubleshooting
situations where the input capacitor bank can discharge
and corrective action of the inverter. Become familiar with
through the short). Failures may be evident upon inspection.
all of the malfunctions listed before proceeding. Some
Voltages should not be applied to the unit until it has been
malfunctions are similar but have different causes. The
signal waveforms referenced in this table are shown in
opened and visually inspected for burned or otherwise
damaged components. Where failed circuits are
Table 3-6. Troubleshooting Chart
1. Excess input
Vin less than 1
a. Disconnect P1 at J1.
M28 V dc bus
a. Ohmeter Xl scale
a.Disassemble unit as
volt. I is greater
plus probe at J1-C,
shorted to ground.
than 2 amps.
minus probe at
leads. Large capacitor
bank will charge up.
b. Use standard VOM
b. Inspect for pinched or
broken wires. Repair
to check Ji-C for a
short to the chassis.
c. There are 5 areas
which may be shorted.
may be shorted. The
A44 I/0 filter, the A13
capacitor bank, the Al
pulscr assy, A24Q16,
and the A22 printed
Disconnect the wiring
as necessary to isolate
the short to a
particular item. Repair
or replace the item as
a. Signals should
a. Remove right side
a. Disassemble unit to
2. Excess input
Vin approximately a. Improper
transistor cover panel,
gain access to circuit
duplicate A19 and
5-7 volts. I is
boards A21 and A22,
pars 3-11. use
A20 in phase with
greater than 10.
scilloscope to check
appropriate OA, OB
Inspect for burned or
amps. No load.
signals at transistor
or OC output
R120. Also A21Q5, Q9,
R16, Q105, Q109 and
R116. Replace both