Tektronix 2445, Инструкция по эксплуатации

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Maintenance— 2445 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. To
provide correct orientation of a multipin connector, an index
arrow is stamped on the circuit board, and either a matching
arrow is molded into or the numeral 1 is marked on the
plastic housing as a matching index. Be sure these index
marks are aligned with each other when the multipin con­
nector is reinstalled.
TRANSISTORS, INTEGRATED CIRCUITS,
AND HYBRID CIRCUITS
Transistors, integrated circuits, and hybrid circuits should
not be replaced unless they are actually defective. If re­
moved from their sockets or unsoldered from the circuit
board during routine maintenance, return them to their origi­
nal board locations. Unnecessary replacement or transpos­
ing 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 “Dia­
grams” section for lead-configuration illustrations.
The heat-sink-mounted power supply transistors are in­
sulated from the heat sink with a heat-transferring insulator
pad. Reinstall the insulator pads and bushings when replac­
ing these transistors. Do not use any type of heat-transfer­
ring compound on the insulator pads.
N O T E
A fte r replacing a p o w e r transistor, check th a t th e col­
lecto r is n o t sh orted to the h e a t sink before applying
p o w e r to the instrum ent.
To remove socketed dual-in-line packaged (DIP) integrat­
ed circuits, pull slowly and evenly on both ends of the de­
vice. 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 1C when it is going to be re­
placed, clip all the leads of the device and remove the leads
from the circuit board one at a time. If the device must be
removed intact for possible reinstallation, do not heat adja­
cent conductors consecutively. Apply heat to pins at alter­
nate sides and ends of the 1C as soider is removed. Aiiow 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 housing will aid in removal of the nuts. The hybrid
circuit substrate is bonded to the heatsink/housing casting.
Attempting to separate the hybrid device from its housing
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.
JVARNI^
f^ J j
To avo id an electric-shock hazard, observe the follow­
ing precautions b efore attem pting an y soldering: turn
the instrum ent off, disconnect it from the ac p o w er
source, an d verify th a t the lin e-rectifier filte r capacitors
have discharged. (S ee lab el on the p rim ary p o w er
shield.) If, due to a com ponent failure, the capacitors
a re n o t discharging, it m ay be necessary to discharge
them . U se a 1 kQ, 5 -w a tt resisto r a n d discharge the
capacitors from p o in t to p o in t through th e access
holes in the p rim ary p o w er 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 high­
er wattage soldering iron may cause etched circuit conduc­
tors 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 enough solder to make a firm
joint. After soldering, clean the area around the solder con­
nection with an approved flux-removing solvent (such as
isopropyl alcohol) and allow it to air dry.
Circuit boards in this instrument may have as many as
four conductive layers. Conductive paths between the top
and bottom board iayers may connect to one or more inner
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