Theory of Operation-2445A/2455A Service
Power Supply Shutdown
Phosphor damage
can
occur to the CRT if certain regu-
lated power supply voltages are overloaded
due
to exces-
sive current draw
by
their loads. U1300C
and
its associ-
ated circuitry monitor the + 15 V
and
the
+ 5 V Regulator
supplies.
The
+87
V
and
the
+42
V Regulator supplies
are
monitored
via
R1294
and
R1295
respectively. If
any
of
these regulated supplies exceed their limit, current
is
sourced
to
U1300D
(pin
13).
When
this happens, the
+ 1 0 V Reference begins to drop which
in
turn lowers all
the regulated supplies. This causes the high voltage oscil-
lator to shutdown preventing damage to the
CRT.
01290
and
its associated circuitry allows the + 10 V Reference to
come
up
and
stabilize before the shutdown circuitry
is
enabled.
Jumper J208 is
used
to disconnect the shutdown
circuitry for troubleshooting purposes.
POWER DISTRIBUTION
Schematic diagrams
11
and
12 illustrate the power dis-
tribution of the instrument.
The
connections to
the
labeled
3-46
I o
boxes (representing the hybrids
and
ICs)
show the power
connections to
each
device, while connections to non-
power lines
are
shown by the component
and
schematic
number. Power supply decoupling
is
done
with traditional
LRC
networks
as
shown
on
the diagrams.
Several intermediate supply voltages
are
generated by
devices shown
on
diagrams
11
and
12.
An
approximate
+32
volt supply for the A
and
B Sweeps
is
developed by
emitter-follower 0700
and
its associated components.
Zener diodes VR125
and
VR225 develop approximate
+6.2
volt supplies for the
CH
1
and
CH
2 Preamps
respectively,
and
zener
diode VR2805 establishes
an
approximate
-6.8
volt supply for U2800
and
U2805.
INTERCONNECTIONS
Schematic diagram
13
illustrates the circuit board inter-
connections of the instrument. Connector numbers
and
cabling types are shown.
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