TM 55-4920-328-13
5-21. Troubleshooting Electrical Systems Using
Standard Techniques.
Troubleshooting the following systems consists of
the use of standard continuity checks and voltage,
frequency, and polarity checks. These systems are
defined as follows:
Power Distribution System (figure FO-2)
AC/DC Control Distribution System (Figure FO-3)
System Power Interface (figure FO-4)
Auxiliary Services System (figure FO-5)
Fuel and Air Pressure System (figure FO-10)
Fuel Heater Valve and Start Interlock System
(figure FO-15)
Hydraulic Start System (figure FO-18)
Bleed Band System (figure FO-23)
Operator's Panel Assembly (figure FO-24)
Services System (figure FO-25)
5-22. Detailed Electrical Troubleshooting
Procedures.
The systems incorporated in METS which utilize a
monitoring and display system are outlined in the
following text. Where a component is shown without
internal circuitry, it must be assumed that input and
output leads are directly connected to one another. As
an example, if a wire is shown coming into a component
in pin A of an input connector, the signal on that wire
goes straight through the unit and comes out on a
corresponding pin of the output connection. Where a
signal is internally diverted in a component for switching
or signal conditioning, the applicable circuit is shown, or
reference to another schematic is made. The test
equipment
required
for
troubleshooting
individual
systems is identified by manufacturer's part or model
number, except for standard voltmeters, frequency
meters, ammeters, and ohmmeters or multimeters.
5-23. High Temperature System.
Troubleshoot
the
high
temperature
system
in
accordance with the circuit information shown in figure
FO-6 located in the back of this manual and figure 5-4
located in the back of this chapter. Proceed as follows:
a.
With all system electrical power deenergized,
accomplish continuity checks of system wiring and
interconnect cabling. Check all connections for
intermittent shorts, opens, and grounds.
b.
Energize the METS electrical systems as
specified in chapter 2, Preliminary Checkout Prior to
Test paragraph. Allow the specified warm-up and
stabilization period.
c.
Use a standard voltmeter to check all power
and signal voltages noted in figure FO-6, observing
polarity.
NOTE
If an alarm is initiated by the application of a
millivolt signal in a circuit at 11J18, depress
the ACK switchlight unit on services panel 4A1
to silence the audible alarm.
d.
Apply +31.65mv dc to 11J18-A(+) and -B(-)
using a precision dc millivolt source. Check the millivolt
signal at terminals 1A7TB2-10 and -11. If no signal is
present, the circuit is open.
e.
Check the dc mv signal at 3A4J1-P and R. If
no signal is present at these points, the engine safety
unit 3A4 is defective.
f.
If a dc mv signal is present at 3A4P2-A and -
B and no temperature is displayed on meter 3A2M1, the
meter is defective.
g.
Check the dc mv signal at 3A3J1-u and -r,
and at 3A3J3-J and -K. If the signal input to 3A3 is
present and no output signal is available at 3AJ3-J and -
K, troubleshoot the components within operator's panel
assembly 3A3 to isolate the defective component.
NOTE
When signal conditioning is not required
within a component, the input signal is
transferred straight through the unit. As an
example, if a signal is input to a unit on pins A
and B, the output of the circuit may be picked
up at pins A and B (or corresponding pins) on
the output connector. The METS interconnect
cables
are
also
wired
in
this
manner.
Likewise, signals input to a unit on numbered
pins or terminals are normally output on
corresponding pin or terminal numbers.
h.
Check
the
millivolt
signal
level
at
1A9J11(+)(CR) and -1(-)(AL). If no output signal is
present at these points, thermocouple reference junction
1A9 is defective.
5-28
