Tektronix 114, Instruction Manual

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SECTION 4
MAINTENANCE AND
CALIBRATION
Preventive Maintenance
Preventive maintenance consists of cleaning, visual inspec­
tion, lubrication, and if needed, recalibration. Preventive
maintenance is generally more economical than corrective
maintenance since preventive maintenance can usually be
done during idle periods at a time convenient to the user.
The preventive maintenance schedule established for the
instrument should be based on the amount of use and the
environment in which the instrument is used.
Cleaning. Clean the instrument often enough to prevent
accumulation of dirt. Dirt on the components acts as an
insulating blanket (preventing efficient heat dissipation) and
may provide conducting paths.
Clean the instrument by loosening the accumulated dust
with a dry, soft paint brush. Remove the loosened dust by
vacuum and/or dry, low pressure compressed air (high
velocity air can damage certain components). Hardened
dirt and grease may be removed with a cotton-tipped swab
or a soft cloth dampened with water and a mild detergent
solution (such as Kelite or Spray White). Abrasive cleaners
should not be used.
CAUTION
Do not permit water to get inside controls or shaft
bushings.
Lubrication. The life of potentiometers and rotary switches
is lengthened if these devices are kept properly lubricated.
Use a cleaning type lubricant (such as Cramoline) on shaft
bushings and switch contacts. Lubricate the switch detents
with a heavier grease (Beacon grease No. 325 or equiva­
lent). Do not over-lubricate. The necessary materials and
instructions for proper lubrication of Tektronix instruments are
contained in a component lubrication kit which may be
ordered from Tektronix. Order Tektronix Part No. 003-342.
Visual Inspection. After cleaning, the instrument should
be carefully inspected for such defects as poor connections,
damaged parts, and improperly seated transistors. The rem­
edy for most visible defects is obvious; however, if heat­
damaged parts are discovered, determine the cause of
overheating before the damaged parts are replaced. Other­
wise, the damage may be repeated.
Transistor Checks. Periodic preventive maintenance
checks consisting only of removing the transistors from the
instrument and testing them in a tester are not recommend ­
ed. The circuits within the instrument provide the most
satisfactory means of checking transistor performance. Per ­
formance of the circuits is thoroughly checked during cali ­
bration so that substandard transistors will be detected at
this time. Check suspect transistors by substitution. Be sure
the substituted transistor is the same type as the one re ­
placed, and that the substitute itself is good. If the original
transistor is found to be good, return it to the same socket
from which removed.
Recalibration. Instrument accuracy is ensured if the cali­
bration of the Type 114 is checked after every 500 hours
of operation (every six months if the instrument is used inter­
mittently). Complete recalibration instructions are contained
later in this section.
The calibration procedure is helpful in isolating major
troubles in the instrument. Moreover, minor troubles not
apparent during regular operation may be revealed and
corrected during recalibration.
Corrective Maintenance
General Troubleshooting. If the instrument is not op ­
erating, attempt to isolate the trouble by a quick opera ­
tional and visual check. Make sure that any apparent
trouble is actually due to a malfunction within the Type
114 and not due to improper control settings or a fault in
associated equipment.
Operate the front-panel controls to see what effect, if
any, they have on the trouble symptoms. The normal or
abnormal operation of each particular control helps in
establishing the nature of the trouble. The normal function
of each control is listed in Section 2 of this manual.
If the trouble cannot be located by means of front-panel
checks, remove the instrument from its case and check volt­
ages and waveforms against those shown on the schematics
in Section 5, starting with the power supply connections.
Once the trouble is isolated to a particular circuit, refer to
the circuit description in Section 3 for an explanation of
how the circuit normally operates.
CAUTION
Be careful when making measurements on live
circuits. The small size and high density of com ­
ponents used in this instrument result in close spac­
ing. An inadvertent movement of the test probes,
or the use of oversized probes, may short between
circuits.
Helpful Hints:
1. Check the voltage between chassis ground and the
top end of R244 (333 Ω 10 watt resistor mounted at the
top-right-rear of the chassis). With normal line voltage,
the voltage at the top of R244 should read 31 to 35 volts
if the AMPLITUDE switch is set to +; 6 to 10 volts if the
switch is set to — .
2. Set the AMPLITUDE switch to + and turn off the power.
Using an ohmmeter, check the resistance from the top end
of R244 to chassis ground. If there is no charge on the
filter capacitors, the resistance reading should be about
800 Ω to 2 k. If it is not, reverse the meter leads and re ­
check.
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