BFGoodrich Avionics
Systems,
Inc.
Component
Maintenance Manual
P/N
501-1075-()
G.
Battery
Test Circuit
(if present)
The
Battery
Test
Circuit is
present on
unit models designated _/T. The
assembly level
designation is
A3 as
indicated
in
Figure
4
of
this
section,
the
schematics for /T
models
in
the
Fault Isolation
section and
IPL
Figure 6 in the
Illustrated
Parts
List
section.
CAUTION: IMPROPEROPERATIONOFTHETEST
CIRCUITCAN
DAMAGETHE
UNIT
AND
MAKE
THE
TESTINDICATOR
USELESS.DO
NOTATTEMPTTHETESTAGAINFOR
2
TO
3 MINUTES.
SEE
THE
CHECKSSECTION
OFTHIS
MANUALFORPROPEROPERATION.
The
battery
test circuit operation is initiated
by
depressing the test
button, typically
mounted
in
the cockpit. When
the
test
button is
depressed, 28Vdc is applied to
relay A3Kl and
to
the
bases
of transistors
A3Q3and
A3Q4
biases
the
400Hz
oscillator
OFF
during the battery
test.
Relay A3Kl is energized
when
the
28Vde
applied through resistor A3R1 biases transistor
A3Q1ON completing a
current path from power
ground through
diode
A3CR2,
transistor
A3Q1,and relay
winding
A3Kl
to the
test
switch and 28Vdc. Relay A3Kl contacts
3
and4
open disconnecting
the 28Vde input
from
pin
J1-10.
Contacts
7
and
8
close
completing
a
current path from the emitter
of
transistor
A3Q5through
relay
A3K
l to
power
ground. When
ground is connected
to
transistor
A3Q5,
a resistive
load
made
up
of
resistor A3R6
and
A3R7
is
simultaneously
connected between
the battery
output and
power
ground. Current flow
through
resistors A3R7
and A3R8
develops a
positive voltage at the junctionof capacitor A3C2 and
zener diode
A3CR5. Capacitor A3C2
charges to a
calibrated
voltage
representative
of
the
battery
output
voltage.
If the
battery
voltage is
within
calibrated
limits,
zener
diode
A3CR5
will apply
a
positive
voltage to the base
of transistor
A3Q4.
The conduction of transistor A3Q4
causes
a positive
voltage
drop
across resistor
A3R10 that in
turn
biases transistor
A3Q5
on.
Electron current flow
is from
power ground
through relay A3Kl,
contacts
7 and
8, through
transistor A3Q5,and
diode
A3CR6
to
the
test lamp. The test
lamp,
mounted near the test
button,
will
illuminate
indicating
that the battery output voltage is acceptable.
When the positive voltage
on
capacitor A3Cl reaches a sufficient
level,
zener diode A3CR3
applies
the
voltage to
the
base of
transistor
A3Q3biasing
the
transistor
ON.
Current flow
through
resistor A3R2 develops
a positive
voltage on the base
of transistor A3Ql.
The
positive
voltage on the base of transistor
A3Ql
will
bias the transistor
OFF.
Current
flow through
transistor
A3Qland
the
winding of relay A3Kl
will
be zero.
Relay
A3Kl will
de-energize
disconnecting
the
resistive load
from the
battery
and
reconnecting the
28Vdc
input
at
pin
Jl-10.
Note
that
relay
A3Kl
is
automatically
de-energized after approximately
4 seconds
after
the
beginning of the
test
in this paragraph.
However,
the 400Hz oscillator will
be
biased OFF as
long
as
the test switch is ON. To recycle
the
battery
test
circuit,
it
is necessary
to
momentarily
open the
test switch so
that capacitor
A3Cl
can
discharge sufficiently to
tum transistors
A3Q3
and A3Q2OFF.
msmljtp202DescriptOpsdiskl59
24-20-03
Page 7
Revision
A
June
30, 1999
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