Maintenance—475
merit, particularly at high frequencies. AH replace
ment parts should be direct replacements unless it is
known that a different component will not adversely
affect instrument performance.
Special Parts. In addition to the standard electronic
components, some special components are used in the 475.
These components are manufactured or selected by
Tektronix, Inc. to meet specific performance requirements,
or are manufactured for Tektronix, Inc. in accordance with
our specifications. These special components are indicated
in the Electrical Parts List by an asterisk preceding the part
number. Most of the mechanical parts used in this
instrument have been manufactured by Tektronix, Inc.
Order all special parts directly from your local
TEKTRONIX Field Office or representative.
Ordering Parts. When ordering replacement parts from
Tektronix, Inc., it is imperative that all of the following
information be included in the order to ensure receiving the
proper parts.
1. Instrument type.
2. Instrument serial number.
3. A description of the part (if electrical, include the
circuit number).
4. TEKTRONIX Part number.
Soldering Techniques
WARNING I
Always disconnect the instrument from the power
source before attempting to solder in the instrument.
Ordinary 60/40 solder and a 35- to 40-watt pencil-type
soldering iron can be used to accomplish the majority of
the soldering to be done in the 475. If a higher wattage
rating soldering iron is used on the etched circuit boards,
excessive heat can cause the etched circuit wiring to
separate from the board base material.
The Vertical Preamplifier Attenuator circuit boards
are made of material easily damaged by excessive
heat. When soldering to these boards, do not use a
soldering iron with a rating of more than approxi
mately 15 watts. Avoid prolonged applications of
heat to circuit-board connections. Use only isopropyl
alcohol when cleaning this circuit board.
When soldering to the ceramic strips in the instrument a
slightly larger soldering iron can be used. It is recommended
that a solder containing about 3% silver be used when
soldering to these strips to avoid destroying the bond to the
ceramic material. This bond can be broken by repeated use
of ordinary tin-lead solder or by the application of too
much heat; however, occasional use of ordinary solder will
not break the bond if excessive heat is not applied.
If it becomes necessary to solder in the general area of
any of the high-frequency contacts in the instrument, clean
the contacts immediately upon completion of the soldering.
Refer to the section entitled Switch Contacts under
PREVENTIVE MAINTENANCE for recommended cleaners
and procedures.
Component Replacement
WARNING
Always disconnect the instrument from the power
source before attempting to replace components.
Circuit Board Replacement. Occasionally it may be
necessary to gain access to the reverse side of a circuit
board or to remove one circuit board to gain access to
another. The following procedures outline the necessary
steps to facilitate instrument disassembly. Most of the
connections to the circuit boards in the instrument are
made with pin connectors. However, some connections are
soldered to the board. Observe the soldering precautions
given under Soldering Techniques given in this section.
Vertical Preamp Circuit Board Removal
1. Unplug the delay line from the Vertical Preamp
circuit board.
2. Unplug the six coaxial cables and one wire from the
front side of the Vertical Preamp circuit board. Note wire
color codes to facilitate correct reinstallation.
3. Unplug the two coaxial cables from the back side of
the Vertical Preamp circuit board. Note wire color codes to
facilitate correct reinstallation.
4. Unplug a 6-wire, a 7-wire, and a 10-wire ribbon cable
from the Vertical Mode Switch circuit board.
4-3
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