Tektronix 3B2 TIME-BASE Instruction Manual page 15

SECTION 5
MAINTENANCE
PREVENTIVE MAINTENANCE
Visual Inspection
The Type 3B2 should be inspected occasionally for such
visual defects as poor connections, broken or damaged
ceramic strips, improperly seated tubes or transistors, and
heat-damaged parts. The remedy for most visual defects is
obvious; however, particular care must be taken if heat-
damaged parts are detected. Overheating can be caused
by other, less apparent troubles in the circuit. For this reason,
it is essential to determine the actual cause of overheating
before the parts are replaced; otherwise, the damage may
Recalibration
The Type 3B2 is a stable instrument and should provide
many hours of trouble-free operation. To maintain measure-
ment accuracy, however, we suggest a calibration check after
each 500 hours of operation (or every six months if used
intermittently). Complete calibration instructions are con-
tained in Section 6 of this manual. The calibration pro-
cedure includes steps which will help check for proper opera-
tion of various circuits. Minor troubles not apparent during
regular operation will often be revealed during calibration.
Also, major troubles in the instrument can often be isolated
or eliminated by calibrating the instrument.
PARTS REMOVAL AND REPLACEMENT
General Information
Removal or replacement procedures for most parts in the
instrument are obvious. However, some parts require special
procedures. Removal and replacement of these parts are
discussed in the following paragraphs.
Many components in the instrument are mounted in a
particular way to reduce stray inductance and capacitance.
Therefore, carefully install replacement components to dupli-
cate lead length, lead dress, and location of the original
After replacing any electrical components, be sure to
check the calibration of the instrument. Components of the
same type may exhibit slightly different characteristics, and
may affect calibration.
Tubes and Transistors
Tubes or transistors should not be replaced unless they
are actually defective. If tubes or transistors are removed
and found to be acceptable, be sure to return them to their
original sockets. This will avoid recalibration because of
different tube or transistor characteristics.
®
The best way to check a tube or transistor is by sub-
stitution. That is, replace the suspected tube or transis-
tor with one of the same type that you know is good. Then,
check to see if the instrument operates properly. If not,
return the original tube or transistor to its socket.
Wafer Switches
Individual wafers are normally not replaced in the switch
assemblies. If one wafer is defective, the entire switch as-
sembly should be replaced. Switches can be ordered from
Tektronix either wired or unwired.,
The wafer switches shown on the schematics are coded to
indicate the position of the wafer on the switch. The wafers
are numbered from front to rear (i.e., the number 1 wafer is
always closest to the front panel). The letters F and R indi-
cate the front or rear of the wafer. For example, a code
designation of 3R means the rear side of the third wafer
from the front panel.
Soldering Precautions
In the production of Tektronix instruments, a silver-bearing
solder is used to establish a bond to the ceramic terminal
strips. This bond may be broken by repeated use of ordinary
tin-lead solder, and by excessive heating of the terminal strip
with a soldering iron. Occasional use of ordinary solder is
permissible if applied with moderate heat. For general re-
pair work, however, solder used for the ceramic strips should
contain about 3% silver. If this type of solder is not avail-
able locally, it may be purchased directly from Tektronix
in one-pound rolls (part number 251-514).
A wedge-shaped tip on the soldering iron is best for
soldering or unsoldering parts on the ceramic strips. This
type of tip allows you to apply heat directly to the solder-
slot on the strip, reducing the overall heating affect. Use
as little heat as possible to establish a good solder bond.
The following procedure is recommended for soldering
and unsoldering short-lead components: (1) Use long-nose
pliers for a heat sink. Attach the pliers between the com-
ponent and the point where the heat is applied. (2) Use a
hot soldering iron for a short time. (3) Carefully manipulate
the leads to prevent lead or insulation damage. (4) Use
only a small amount of solder; just enough to make a
Ceramic Terminal Strips
To remove a ceramic terminal strip, first unsolder all
leads and components connected to it. The pry the strip,
with yokes attached, out of the chassis. The spacers may
come out with the yokes; if not, they can be pulled out
separately. If they are not damaged, the spacers may be
used with the new strip assembly.