SECTION 4
MAINTENANCE
PREVENTIVE MAINTENANCE
The M Unit is a stable instrument, and will require com
plete calibration very infrequently. However, to be certain
that the unit is operating properly at all times, the calibra
tion of the unit should be checked after each 500-hour
period of operation (or every six months if the unit is used
intermittently). A complete step-by-step procedure for cali
brating the unit and checking its operation is given in the
Calibration section of this manual.
Visual Inspection
Many potential and existent troubles can be detected by
a visual inspection of the unit. For this reason, a complete
visual check should be performed if the unit becomes inop
erative, or needs repair or recalibration. Apparent defects
may include loose or broken connections, damaged con
nectors, improperly seated tubes or transistors, scorched or
burned parts, and broken terminal strips. The remedy for
these troubles is readily apparent, except for heat-damaged
parts. Heat damage to parts is often the result of other,
less apparent troubles. It is essential to determine the cause
of overheating before replacing the damaged parts.
COMPONENT REPLACEMENT
General
Parts replacement information is contained in this portion
of the manual. Because of the circuit configuration, re
placement of certain parts, such as the VOLTS/CM switches,
variable inductors, transistors or tubes, will require recalibra
tion of the instrument to insure proper operation. Refer to
section 5 for calibration instructions.
Switches
If a switch is defective and needs repair or replacement,
use care in unsoldering and disconnecting the leads.
Single wafers on wafer-type switches are not normally
replaced. If a wafer is defective, the entire switch should
be replaced. Some switches may be ordered from the fac
tory either unwired or wired with components mounted, as
desired. Refer to the Parts List to find the unwired and wired
switch part numbers.
When soldering the leads to one of the wafer-type
switches, do not let solder flow around and beyond the
rivet on the switch terminal. Otherwise the spring tension
of the switch contact can be destroyed.
Soldering Precautions
In the production of Tektronix instruments, a special
silver-bearing solder is used to establish a bond to the
ceramic terminal strips. This bond can be broken by re
peated use of ordinary tin-lead solder, or by the applica
tion of too much heat. However, occasional use of ordinary
solder will not break the bond if too much heat is not
applied.
It is advisable to have a stock of solder containing about
3% silver if you frequently perform work on Tektronix
instruments. This type of solder is used in printed circuitry
and should be readily available. It may also be purchased
directly from Tektronix in one-pound rolls (order by part
number 251-514).
Because of the shape of the terminals on the ceramic
terminal strips, it is advisable to use a small diameter
wedge-shaped tip on your soldering iron when installing
or removing parts from the strips. A wedge-shaped tip
allows you to apply heat directly to the solder in the termi
nals and reduces the amount of heat required. It is im
portant to use as little heat as possible. Fig. 4-1 shows the
correct shape for the tip of the soldering iron. Be sure to
file smooth the surfaces of the tip before tinning. This pre
vents solder from building up on rough spots where it can
quickly oxidize.
Fig. 4 -1 . Soldering iron tip properly shaped and tinned.
4-1
