Tektronix TM 503 User Manual

known to be operating properly. !f the trouble persists after
substitution, then the power module is probably at fault.
Moving a properly operating plug-in from compartment to
compartment will help determine if one or more compart-
ments has a problem,
Visual Check
Inspect the portion of the system in which the trouble is
suspected. Many troubles can be located by visual clues
such as unsoldered connections, broken wires, damaged
circuit boards, damaged components, etc.
Instrument Calibration
Check the calibration of the suspected plug-in module or
the affected circuit if the trouble is obviously in a certain
circuit. The trouble may only be a result of misadjustment
or may be corrected by re-calibration. Complete calibration
instructions are given in the manual for each instrument in
the system.
Circuit Isolation
Note the symptom. it often identifies the circuit in
which the trouble is located. When trouble symptoms
appear in more than one circuit, check the affected circuits
by making waveform and voltage measurements.
Incorrect operation of alf circuits often means trouble in
the power supplies. Using a multimeter, check first for
correct voltages of the individual regulated supplies
according to the plug-in module schematics and calibration
procedures, Then check the unregulated supplies of the
power modules. Defective components elsewhere in the
instruments can appear as power supply problems. In these
instances, suspected circuits should be disconnected from
apparently bad power supplies one at a time to narrow the
search.
Voltages and Waveforms
Often defective components can be located by using
waveform and voltage indications when they appear on the
schematic or in the calibration procedures. Such waveforms
and voltage labels are typical indications and will vary
between instruments. To obtain operating conditions
similar to those used to take these readings, refer to the
first diagram in the service sections.
Component Checking
'f
a
component
cannot
be
disconnected
from
its
circuit,
then
the
effects
of
the
associated
circuitry
must
be
considered
when
evaluating
the
measurement.
Except
for
soldered
in
transistors
and
integrated
circuits,
most
compo-
nents
can
be
lifted
at
one
end
from
the
circuit
board.
®
System Maintenance—TM 503
Transistors and [C’s. Turn the power switch off before
removing or replacing any semiconductor.
A good check of transistor operation is actual perform-
ance under operating conditions. A transistor can most
effectively be checked by substituting a new component for
it (or one which has been checked previously). However, be
sure that circuit conditions are not such that a replacement
transistor might also be damaged. {f substitute transistors
are not available, use a dynamic tester. Static-type testers
are not recommended, since they do not check operation
under simulated operating conditions. A suction-type
desoldering tool must be used to remove soldered-in
transistors; see component replacement procedure for
details.
Integrated circuits can be checked with a voltmeter, test
oscilloscope, or by direct substitution. A good under-
standing of the circuit description is essential to trouble-
shooting circuits using IC’s, Operating waveforms, logic
levels, and other operating information for the IC’s are
given in the circuit description information of the appro-
priate manual. Use care when checking voltages and
waveforms around the IC’s so that adjacent leads are not
shorted together. A convenient means of clipping a test
probe to the 14- and 16-pin in-line [C’s is with an
integrated-circuit test clip. This device also doubles as an
extraction tool.
Diodes. Do not use an ohmmeter that has a high internal
current, High currents may damage the diode.
A diode may be checked for an open or shorted
condition by measuring the resistance between terminals.
With an ohmmeter scale having an internal source of
between 800 mV and 3V, the resistance should be very
high in one direction and very low when the leads are
reversed.
Resistors. Check the resistors with an ohmmeter, Resis-
tor tolerances are given in the Electrical Parts List in every
manual. Resistors do not normally need to be replaced
unless the measured value varies widely from the specified
value,
Capacitors. A leaky or shorted capacitor can be detected
by checking resistance with an ohmmeter on the highest
scale. Use an ohmmeter which will not exceed the voltage
rating of the capacitor. The resistance reading should be
high after initial charge of the capacitor. An open capacitor
can best be detected with a capacity meter, or by checking
whether it passes AC signals.
10

Tektronix TM 503 Specifications

General

Brand	Tektronix
Model	TM 503
Category	Control Unit
Language	English