Transistors And Integrated Circuits; Soldering Techniques - Tektronix 2205 Service Manual

Maintenance—2205 Service
TRANSISTORS AND INTEGRATED
CIRCUITS
Transistors and integrated circuits should not be
replaced unless they are actually defective. If
removed from their sockets or unsoldered from the
circuit board during routine maintenance, return
them to their original circuit board locations. Un­
necessary replacement or transposing of semi­
conductor 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.
Power-supply transistors Q933. Q942, and Q946
are insulated from the chassis by a heat-transferring
pad and insulation bushing. Reinstall the pad and
bushing when replacing this transistor.
6-12
After replacing a power transistor, check that
the collector is not shorted to the chassis
before applying power to the instrument.
To remove
(DIP) integrated circuits, puli 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 1C when it is going to
be replaced, clip all the leads of the device and re­
move the leads from the circuit board one at a time.
If the device must be removed intact for possible
reinstallation, do not heat adjacent conductors con­
secutively. Apply heat to pins at alternate sides and
ends of the 1C as solder is removed. Allow a
moment for the circuit board to cool before
proceeding to the next pin.

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.
To avoid an electric-shock hazard, observe
the following precautions before attempting
any soldering: turn the instrument off, dis­
connect it from the ac power source, and wait
at least three minutes for the tine-rectifier
filter capacitors to discharge.
Use rosin-core wire solder containing 63% tin
and 37% lead. Contact your local Tektronix Field
Office or representative to obtain the names of
approved solder types.
.......
When soldering on circuit boards or small insu­
lated wires,
soldering iron. A higher wattage soldering iron may
cause etched-circuit conductors to separate from
the circuit board base material and melt the insu­
lation 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 connection with an
approved flux-removing solvent (such as isopropyl
alcohol) and allow it to air dry.
NOTE
socketed, dual-in-line-packaged
WARNING I
use only a 15-watt, pencil-type