Model
5315A
/ B
Service
8-12
8-73.
Du
ring charg
in
g, current flows from the
500
mA
and/
or
the
10
mA
regulators
through
battery BTl, fuse
Fl
, and curr
ent
sensing resistor
R18
.
Th
e voltage develo
ped
across this network
is monitored
by
the charge
co
mparator, made up of cascaded comparators
U2
B and
U2C,
temperature
compe
nsating thermistor
RTl
and associated circuitry through
R16
and
CR6.
Th
e charge level
on
U2
pin 6
is
compared
against the reference voltage
on
pi
n 5, from
the
2.5V
refer
ence
regulator
U3.
The
output
of
the
charge compa rator, responding to
the
charge require-
ments of the battery, turns
regulator
U2
on
and off v
ia
CR10
and
CR9.
During ac operation,
U2
(C)
is
di
sabled
by
the
+5V
supply from the motherboard, v
ia
CR3.
CR2
and
CR4
form a
diode
OR-gate,
supp
lying voltage from
either
the unregulated
dc
(line)
or
the
battery, to
2.5V
refer-
ence
regulator
U3.
8-74. The l
ow
battery
detector,
consisting of
USA
,
USB
, Q14. and associated circuitry, monitors
the
switched battery voltage during discharge. When the battery voltage at pin 6 drops below the
reference
level set at pin
5,
U5
pin 7 goes high, which disabl
es
the
DC-Io-DC convert
er
(
U1
pin 2
),
and the
+3
and +5 regulators (
on
the
motherboard)
via
the
shut-
down
line.
Thi
s enables the l
ow
battery oscillator,
U4B
and associated circuitry, which blinks
the
discharge light through
U4D
and
Q8. When
the
battery voltage at pin 6
is
above
the
reference,
US
pin 7 goes l
ow
, which turns
on
the dischar
ge
light continuously, through
U4C,
U4A
,
U4D,
and
08.
07
,
CR3,
and associated
circuitry are
support
circ
ui
try for
USB.
U1
and
05
make up
the
DC-to-DC, which reverses the
polarity of the
po
s
iti
ve
battery voltage, to
produce
the
negative
dc
necessary to drive
the
-5.2
regulator
on
the
motherboard.
8-75.
A7
TCXO
Option
001
8-
76.
The
A7
assembly provides a high stabili
ty
time base oscillator, which replaces
the
intern
al
10
MHz reference v
ia
[NT
/
EXT
sw
itch
53
. Power (
+5V
)
is
f
ed
thr
ough
Pl pin 4 to pin 1 of
the
temperature compensated crystal oscillator (
TCXO
). 10 MHz
is
ouput
, across divider network
Rl
and
R2
, to Pl pin
2.
8-77. TROUBLESHOOTING
TEST
PROCEDURES
8-78. The following test procedures are designed
to
effectively ver
if
y the
proper
operation of
isolat
ed
subsec
ti
ons of the
co
unter.
Ref
er
to
the
trouble
shooting block
di
agram, Figure 8-6, to
det
ermine
the
circuits tested
by
each procedure. Although each
procedure
may
be
performed
independently,
it
is
recommended
that they be performed
in
the
numerical
sequence
as
given.
8-79. Test
Procedure
1, Power Supply
8-80.
To
verify
the
proper
operation of the
53
15A
/ B power
supp
l
y,
measure
the
three
dc
voh-
ages on the labeled test points
on
the
Al
Motherboard. Insure a
ll
three
are within
the
±10 mV
tolerance. readjusting
if
necessary.
Voltage
+
5V
dc
+
3V
dc
-
5.2V
dc
Tolerance
±10
mV
±10
mV
±10
mV
Adjustment
A1R19
A1
R15
A1
R26
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