Tektronix 1A5 Instruction Manual page 39

Maintenance — Type 1 A5
8. Troubleshoot the Type 1A5 circuitry as necessary.
9. Recalibrate the Type 1A5.
Parent Oscilloscope
The quickest check of the oscilloscope is
good plug-in unit, or check the
another oscilloscope. Refer to the oscilloscope
necessary to verify proper operation
Operating Procedures and Control Settings
Refer to the Operating Instructions
to verify operating procedures
tings of the Type 1A5.
Trouble Symptoms
After it is confirmed that a casualty exists, Type 1A5
response to all front panel controls should be observed.
The first-time operation listed in section 2 or the Performance
Check in section 5 can be used for this purpose. All trouble
sympto m s should be evaluated and compared against each
other. A casualty will often create a combination of symp ­
tons that will pinpoint the trouble. A good example of this
is power supply trouble, which will usually cause symptoms
to occur in otherwise unrelated circuits.
Visual Inspection
In physically examining the Type 1A5, take special note
of the area indicated by evaluation of symptoms. Look for
loose or broken connections, improperly seated tubes or
transistors, and burned or otherwise damaged components.
Repair or replace all obviously defective parts. Investigate
the cause of heat damage to components.
Calibration Check
Troubles can frequently be located and corrected by re ­
calibrating the instrument.
nitely been isolated to a specific circuit, it is recommended
that the calibration procedure contained in section 6 be
performed to provide a logical circuit troubleshooting se ­
quence.
Detailed Troubleshooting
General
If the casualty has not been disclosed and corrected
through the procedure outlined, a detailed troubleshooting
analysis will have to be performed. The Circuit Description
section, the Schematic Diagrams,
contained in this section are designed to
shooting.
The Circuit Description section provides a fundamental
understanding of circuit operation and is referenced to the
Schematic Diagrams. The Schematic Diagrams contain volt ­
age and resistance values and signal waveforms. The spec ­
ified operating conditions should
making voltage or waveform comparisons.
NOTE
Voltages and waveforms
tween instruments. Those
4-2
to use it with
questionable plug-in unit with
manual
of the oscilloscope.
section of this manual
and front panel control set ­
Unless the casualty has defi ­
and the troubleshooting aids
expedite trouble ­
be duplicated before
may vary slightly be ­
given in the schematics
should be checked against
it is operating
noted on the schematics for later
Test Equipment Recommended for Troubleshooting
a
The test equipment listed here should
troubleshooting jobs.
if
bration is listed in the Calibration section
High Impedance Voltmeter (20,000 Ω/V
Ohmmeter (2 mA or less current on the
Test Oscilloscope
Flexible Plug-In Extension Cable (Tektronix
0038-00)
Transistor Curve Tracer or Transistor Tester.
DC Balance Check
A properly operating oscilloscope will have its trace cen ­
tered vertically on the CRT only when the Type 1A5 has
a balanced output. The Type 1 A5 is a balanced amplifier.
With no signal or comparison voltage applied to the
gates, any point in the A channel should have a potential
equal (within 50 to 75 mV) to that at
the 8 channel.
If the CRT trace is deflected as a result of a Type
problem, unbalances will exist. They can be detected
connecting a high impedance voltmeter between identi ­
cal points. (A plug-in extension is needed during
cedure to allow access to the points being
If the output balance is checked first and is
work toward the front until an unbalance no longer is de ­
tected. This localizes the trouble to the circuitry between
the points providing balance and those providing
ance.
Some of the Type 1 A5 circuits respond to
with no appreciable voltage change.
above check is not effective at the base of Q374
Q354.
Troubleshooting by Direct
Vacuum tubes and semi-conductor failures
the majority of electronic equipment troubles.
replacing vacuum tubes and transistors often
stitution the most practical means of repair.
is used, these guide lines should be followed:
Determine that the circuit is safe for the
ponent.
Use only substitute components that are
good.
Remove the plug-in from the oscilloscope
stituting components, to protect both you
ment.
Be sure components are inserted properly.
as an aid.
Check operation after each component is
Return good components to their original
each instrument while
properly. Deviations should be
reference.
suffice for most
Test equipment required for re-cali-
of this manual.
DC or greater)
× 1 k scale)
Part No. 012-
an identical
checked.)
current changes
For this reason, the
Replacement
account for
The ease of
makes sub ­
If this method
substitute com ­
known to be
before sub ­
and the equip ­
Use Fig. 4-1
replaced.
sockets.
FET
point in
1A5
by
this pro ­
in error,
unbal ­
or of