Maintenance-2445A/2455A Service
Multipin Connectors
When
pin
connectors
are
grouped together
and
mounted
in
a plastic holder, they
are
removed, reinstalled,
or replaced
as
a unit. If
any
individual wire or connector
in
the assembly
is
faulty, the entire cable assembly should
be
replaced.
Multipin connector orientation
is
indexed by a tri-
angle
on
the cable connector
and
a 1 or triangle
on
the cir-
cuit board. Slot numbers
may
be
molded into the
connector.
Be
sure
these index marks are aligned with
each
other
when
the multipin connector
is
reinstalled.
TRANSISTORS, INTEGRATED CIRCUITS,
AND HYBRID CIRCUITS
Transistors, integrated circuits,
and
hybrid circuits
should not
be
replaced
unless they
are
actually defective.
If
removed
from their sockets or unsoldered from the cir-
cuit board during routine maintenance, return them to their
original board locations. Unnecessary replacement or
transposing of semiconductor devices may affect the
adjustment of the instrument.
When
a semiconductor
is
replaced,
check the performance of
any
circuit that
may
be
affected.
Any
replacement component should
be
of the original
type or a direct replacement.
Bend
transistor
leads
to fit
their circuit board holes,
and
cut the leads to
the
same
length
as
the original component.
See
Figure
9-2
in
the
"Diagrams" section for lead-configuration illustrations.
The
heat-sink-mounted power supply transistors
are
insulated from
the
heat sink with a heat-transferring insu-
lator
pad.
Reinstall the insulator pads
and
bushings when
replacing these transistors.
Do
not
use
any
type of heat-
transferring compound
on
the
insulator pads.
NOTE
After replacing a power transistor, check that
the
collector is not shorted to
the
heat sink before apply-
ing power to
the
instrument.
To
remove socketed dual-in-line packaged
(DIP)
integrated circuits,
pull
slowly
and
evenly on both
ends
of
the
device.
Avoid disengaging one
end
of the integrated
circuit from the socket before the
other,: since this
may
damage the
pins.
To
remove a soldered
DIP
IC
when
it
is
going to
be
replaced,
clip
all
the leads of the device
and
remove
the
6-22
leads from the circuit board
one
at a time. If the device
must
be
removed intact for possible reinstallation,
do
not
heat adjacent conductors consecutively. Apply heat to pins
at alternate sides
and
ends
of the
IC
as
solder
is
removed.
Allow a moment for the circuit board to cool before
proceeding to the next
pin.
Hybrid circuits
and
heatsinks are removed
as
a unit by
removing the mounting nuts
at
the four corners of the
heatsink/housing. A firm downward pressure at the center
of the heatsink will
aid
in
installation/removal of the nuts.
The hybrid circuit substrate
is
bonded to the
heatsink/housing casting. Attempting to separate the
hybrid device from its heatsink will damage the device.
SOLDERING TECHNIQUES
The reliability
and
accuracy of this instrument
can
be
maintained only if proper soldering techniques are
used
to
remove or replace parts. General soldering techniques,
which apply to maintenance of any precision electronic
equipment, should
be
used when working
on
this
instrument.
WAltlfl#G
I
To
avoid
an
electric-shock hazard, observe the
fol-
lowing precautions before attempting any soldering:
turn the instrument
off, disconnect it from the ac
power source, and verify that the line-rectifier filter
capacitors have discharged
(see
label on the primary
power
shield).
If.
due
to a component
failure,
the
capacitors are not discharging,
it
may be necessary
to discharge
them.
Use
a 1 k{} 5-watt resistor and
discharge
the
capacitors from point to point through
the access holes
in
the primary power
shield.
Use
rosin-core wire solder containing
63%
tin
and
37%
lead.
Contact your local Tektronix
Field
Office or represen-
tative to obtain the
names
of approved solder types.
When
soldering
on
circuits boards or small insulated
wires,
use
only a 15-watt, pencil-type soldering iron. A
higher wattage soldering iron
may
cause etched circuit
conductors to separate from
the
board
base
material
and
melt the insulation
on
small wires. Always
keep
the
soldering-iron tip properly tinned to ensure best heat
transfer from the
iron
tip
to
the solder joint. Apply only
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