Tektronix 2445, Instruction Manual

Page: 144 / 351

Maintenance— 2445 Service
agnostic aids inherent in the instrument’s operating
firmware and will locate many circuit faults. The next four
procedures are check steps that ensure proper control
settings, connections, operation, and adjustment. If the
trouble is not located by these checks, the remaining steps
will aid in locating the defective component. When the defec­
tive component is located, replace it using the appropriate
replacement procedure given under “Corrective Mainte­
nance” in this section.
B efore using any test equipm ent to m ake m easure­
m ents on static-sensitive, current-sensitive, o r volt­
age-sensitive com ponents o r assem blies, ensure th at
any voltage o r current supplied b y the te s t equipm ent
does n o t exceed the lim its o f the com ponent to be
tested.
1. Power-up Tests
The 2445 performs automatic verification of much of the
instrument’s circuitry when power is first applied. The “Ker­
nel” tests verify proper operation of the Microprocessor, the
ROM, and the RAM. If all Kernel tests pass, a second level
of checks, the “Confidence” tests, are performed. The Con­
fidence tests, when passed, give the user a high degree of
assurance that the instrument is functioning properly.
If a Kernel test or Confidence test fails, the area of failure
is identified either by a message on the crt (if the instrument
is able to produce a display) or by an error code displayed
on the front-panel LED indicators. If a failure occurs, refer to
the “Diagnostic Routines” discussion later in this section for
definitions of error messages and LED error codes.
Once a problem area has been identified, the associated
troubleshooting procedure should be performed to further
isolate the problem. The troubleshooting procedures are lo­
cated on tabbed-foldout pages in the “Diagrams” section at
the rear of this manual.
2. Diagnostic Tests and Exerciser Routines
Each of the tests automatically performed at power up,
along with several other circuit exercising routines, may be
individually selected by the user to further clarify the nature
of a suspected failure. The desired test or exerciser is se­
lected by “scrolling” through a menu of the available
routines when under control of the “Diagnostic Monitor.”
Entry into the Diagnostic Monitor and its uses are explained
in the “Diagnostic Routines” discussion later in this section.
3. Check Control Settings
Incorrect control settings can give a false indication of
instrument malfunction. If there is any question about the
correct function or operation of any control, refer to either
the “Operating Information” in Section 2 of this manual or to
the 2445 Operators Manual.
4. Check Associated Equipment
Before proceeding, ensure that any equipment used with
the 2445 is operating correctly. Verify that input signals are
properly connected and that the interconnecting cables are
not defective. Check that the ac-power-source voltage to all
equipment is correct.
5. Visual Check
Perform a visual inspection. This check may reveal bro­
ken connections or wires, damaged components, semicon­
ductors not firmly mounted, damaged circuit boards, or
other clues to the cause of an instrument malfunction.
6. Check Instrument Performance and Adjustment.
Check the performance of either those circuits where
trouble appears to exist or the entire instrument. The appar­
ent trouble may be the result of misadjustment. Complete
performance check and adjustment instructions are given in
Sections 4 and 5 of this manual.
7. Isolate Trouble to a Circuit
To isolate problems to a particular area, use any symp­
toms noticed to help locate the trouble. Refer to the trouble­
shooting charts in the “Diagrams” section as an aid in
locating a faulty circuit.
When trouble symptoms appear in more that one circuit,
first check the power supplies; then check the affected cir­
cuits by taking voltage and waveform readings. Check first
for the correct output voltage of each individual supply.
These voltages are measured between the power supply
test points and ground (see schematic diagrams 8, 9, and
10, and associated circuit board illustrations in the “Dia­
grams” section). If the power-supply voltages and ripple are
within the listed ranges, the supply can be assumed to be
working correctly. If they are outside the range, the supply
may be either misadjusted or operating incorrectly.
The Low Voltage Power Supply levels are interdepen­
dent. All the low voltage supplies use the +10 V reference
for their reference levels. If more that one of the low voltage
supplies appears defective, repair them in the following or­
der: + 10 V REF, + 5 V Digital, +87 V, +42 V, +15 V,
+ 5 V Analog, - 1 5 V, - 8 V, and - 5 V.
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