Technical data

64
ing R
3
or R
4
is open.
om the circuit, the
result is a three resistance series cir uit that
can easily be solved to determine I
T
With R removed from the circuit to simulate
be
Sure enough the resultant calculated
tive branch R
3
is the
small 3 or 4 resistance circuits as in the previous examples do not take very many
teps and ar hat if a technician were asked
troublesh umerous connection points?
is always This can be an extremely
elpful reso troubleshooting
equence. o may have to troubleshoot the
ame circuit in a database to determine
h
usions
To further narrow down the possibilities, the circuit can be recalculated assum
This can be done by redrawing and solving the circuit with the absence of one of the parallel
resistances. We will begin by removing R
4
from the circuit.
When R
4
is removed fr
c
.
4
an open, the calculated circuit current is
26.67mA. This does not match the
measured 36.92mA.
From this we can determine that R
4
is not the open resistance and through the process of elimination
R
3
is the only possible component remaining.
In order to verify our theory, the circuit can
same method.
drawn and re-calculated with the absence of R
3
in the
current when R
3
is removed from the circuit
is 36.92mA, a match for the ammeter
reading.
his verifies that resisT
malfunctioning component in the circuit.
Documentation Methods
Troubleshooting
s e fairly easy to recall prior observations and conclusions. W
oot a large electrical circuit with dozens of components and n
wise to docu ach step troubleshooting a circuit.
urce for recalling prior measurements and observations gathered in the
lso be used as a reference for another technician wh
. A log of these troubleshooting documents can be recorded
circuit in Figure T-10. The light bulb refuses to illuminate w
.
to
It m eent when
h
s It can a
s
common faults and failures in the system.
Refer to the en the switch is closed.
Suppose a technician were troubleshooting this circuit. See Figure T-11 for an example of how the
chnician records each of his steps. Notice the table is divided into two columns: Observations and te
Concl
DC
R
1
150
R
2
100
R
3
200
12 V
Ω+Ω+Ω= 200100150
T
R
Ω= 450
T
R
Ω
=
450
12v
I
T
mAI
T
67.26=
Figure T-8
Ω+Ω+Ω= 75100150R
DC
T
Ω= 325
T
R
Ω
=
325
12v
I
T
mAI
T
92.36=
R
1
150
R
2
100
R
4
75
12 V
Figure T-9