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3
1.3.
LEVEL
CONVERTORS
When
the battery
is
being discharged,
(power switch
in
position
"ON", PM2521
disconnected
from
the mains)
the battery
voltage
is
supplied to
V501
.
Due
to
this
the
circuit
which
is
made
by T501
,
A401
(Q3),
R502
begins to
oscillate.
This
oscillation
produces
a positive
voltage
(+13V) on
point
3
of
X101
and
a
negative
voltage
(-13V) on
point
6 of
XI
01 (with respect to
pin
4
of
XI
01).
The
centre pin of
T501
is
fed to
the base of
Q1
(A401) and
this
provides
a
base current
for
V401
and
V402.
The
result
is
a voltage
of
+5V
on
pin
5
of
X101
(with respect to pin
8
of
X101
).
1.4.
SCHMITT TRIGGER
The
Schmitt
trigger circuit consists
of
two
transistors
Q4
and
Q5
(A401
).
When
the voltage of the battery drops
below
5,5V, the Schmitt
trigger
switches the
output
(pin
7 of
X101
)
from
+5V
to
OV
(with respect to pin
8
of
X101).
2
ACCESS
Dismantling the
battery
power
supply:
—
Remove
the
top
cover
as
described
in
Chapter 2
of the
PIV12521 Service
Manual.
—
Disconnect
the
connector
XI
01
.
(Fig. 2,
item
1
.).
—
Remove
the
two
screws
from
the battery
power
supply
cover.
(Fig. 2,
item
2.).
—
Lever
up
the cover
and remove
it.
—
Remove
the
two
screws.
(Fig. 2,
item
3.).
—
The
battery
and
the
printed-circuit
board can
now
be removed.
Fig.
2.
Dismantling
the battery
power
supply
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