Corrective Maintenance; Obtaining Replacement Parts - Tektronix 7B51 Instruction Manual

Maintenance-Type 7851
6. Check Voltages and Waveforms. Often the defective
components can be located by checking for the correct
voltage or waveform in the circuit. Typical voltages and
waveforms are given on the diagrams.
CAUTION
Do not clamp probe to pin connectors as this may
break or damage the connectors.
NOTE
Voltages and waveforms given on the diagrams are
not absolute and may vary slightly between instru-
ments. To obtain operating conditions similar to
those used to take these readings, see the first dia-
gram page.
7. Check Individual Components. The following pro-
cedures describe methods of checking individual com-
ponents in the Type 7B51. Components which are soldered
in place are best checked by disconnecting one end. This
isolates the measurement from the effects of surrounding
circuitry.
A. RELAY. The eight-pin relay used in the Type 7B51
is symmetrical and may be replaced in its socket facing
either direction. This relay, which is plugged into the circuit
board, may be removed and checked. Use an ohmmeter to
check the 600
n
resistance. The relay may also be actuated
by placing +15 volts across the coil. The internal connec-
tions are printed on the body of the relay.
B. TRANSISTORS. The best check of transistor opera-
tion is actual performance under operating conditions. If a
transistor is suspected of being defective, it can best be
checked by substituting a new component or one which has
been checked previously. However, be sure that circuit con-
ditions are not such that a replacement transistor might also
be damaged. If substitute transistors are not available, use a
dynamic tester (such as Tektronix Type 576).
C. DIODES. A diode can be checked for an open or
shorted condition by measuring the resistance between ter-
minals. With an ohmmeter scale having an internal source of
between 800 millivolts and 3 volts, the resistance should be
very high in one direction and very low when the leads are
reversed.
CAUTION
Do not use an ohmmeter scale that has a high internal
current. High currents may damage the diode.
4-6
D. RESISTORS. Resistors can be checked with an
ohmmeter. Check the Electrical Parts List for the tolerance
of the resistors used in this instrument. Resistors normally
do not need to be replaced unless the measured value varies
widely from the specified value.
E. INDUCTORS. Check for open inductors by
checking continuity with an ohmmeter. Shorted or partially
shorted inductors can usually be found by checking the
waveform response when high-frequency signals are passed
through the circuit. Partial shorting often reduces high-
frequency response.
F. CAPACITORS. A leaky or shorted capacitor can
best be detected by checking the resistance with an ohm-
meter on the highest scale. Do 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 capacitance meter or by checking
whether the capacitor passes AC signals.
8. Repair and Readjust the Circuit. If any defective
parts are located, follow the replacement procedures given
in this section. Be sure to check the performance of any
circuit that has been repaired or that has had any electrical
components replaced.
CORRECTIVE MAINTENANCE
General
Corrective maintenance consists of component replace-
ment and instrument repair. Special techniques required to
replace components in this instrument are given here.
Obtaining Replacement Parts
Standard Parts. All electrical and mechanical part re-
placements for the Type 7B51 can be obtained through
your local Tektronix Field Office or representative. How-
ever, many of the standard electronic components can be
obtained locally in less time than is required to order them
from Tektronix, Inc. Before purchasing or ordering replace-
ment parts, check the parts list for value, tolerance, rating
and description.
NOTE
When selecting replacement parts, it is important to
remember that the physical size and shape of a com-
ponent may affect the performance in the instru-
ment, particularly at high frequencies. All replace-
ment parts should be direct replacements unless it is
known that a different component will not adversely
affect instrument performance.