![Tektronix 2445 Instruction Manual Download Page 146](http://html.mh-extra.com/html/tektronix/2445/2445_instruction-manual_1078867146.webp)
Maintenance— 2445 Service
A transistor emitter-to-base junction also can be checked
for an open or shorted condition by measuring the resis
tance between terminals with an ohmmeter set to a range
having a low internal source current, such as the R X 1 kfi
range. The junction resistance should be very high in one
direction and much lower when the meter leads are
reversed.
When troubleshooting a field-effect transistor (FET), the
voltage across its elements can be checked in the same
manner as previously described for other transistors. How
ever, remember that in the normal depletion mode of opera
tion, the gate-to-source junction is reverse biased; in the
enhanced mode, the junction is forward biased.
INTEGRATED CIRCUITS.
An integrated circuit (1C) can
be checked with a voltmeter, test oscilloscope, or by direct
substitution. A good understanding of circuit operation is
essential when troubleshooting a circuit having 1C compo
nents. Use care when checking voltages and waveforms
around the 1C so that adjacent leads are not shorted togeth
er. An 1C test clip provides a convenient means of clipping a
test probe to an 1C.
HYBRIDS.
Hybrid components can best be checked by
observing voltages and waveforms on the circuit board.
Measurements should not be made on any hybrid compo
nent while out of the circuit as they may easily be damaged.
Direct substitution is the best troubleshooting method when
a hybrid failure is suspected.
When checking a diode, do not use an ohmmeter
scale that has a high internal current. High current
may damage a diode. Checks on diodes can be per
formed in much the same manner as those on transis
tor emitter-to-base junctions. Do not check tunnel
diodes or back diodes with an ohmmeter; use a dy
namic tester, such as the TEKTRONIX 576 Curve
Tracer.
DIODES.
A diode can be checked for either an open or a
shorted condition by measuring the resistance between ter
minals with an ohmmeter set to a range having a low inter
nal source current, such as the R X 1 kfi range. The diode
resistance should be very high in one direction and much
lower when the meter leads are reversed.
Silicon diodes should have 0.6 to 0.8 V across their junc
tions when conducting. Higher readings indicate that they
are either reverse biased or defective, depending on
polarity.
RESISTORS.
Check resistors with an ohmmeter. Refer
to the “Replaceable Electrical Parts” list for the tolerances
of resistors used in this instrument. A resistor normally does
not require replacement unless its measured value varies
widely from its specified value and tolerance.
INDUCTORS.
Check for open inductors by checking con
tinuity with an ohmmeter. Shorted or partially shorted induc
tors can usually be found by check the waveform response
when high-frequency signals are passed through the circuit.
CAPACITORS.
A leaky or shorted capacitor can best be
detected by checking resistance with an ohmmeter set to
one of the highest ranges. Do not exceed the voltage rating
of the capacitor. The resistance reading should be high after
the capacitor is charged to the output voltage of the ohm
meter. An open capacitor can be detected with a capaci
tance meter or by checking whether the capacitor passes ac
signals.
ATTENUATORS.
The Attenuators are built as complete
assemblies and should not be taken apart. If an Attenuator
is suspected as having failed, direct substitution is the rec
ommended troubleshooting method.
11. Repair and Adjust the Circuit.
If any defective parts are located, follow the replacement
procedures given under “Corrective Maintenance” in this
section. After any electrical component has been replaced,
the performance of that circuit and any other closely related
circuit should be checked. Since the power supplies affect
all circuits, performance of the entire instrument should be
checked if work has been done on the power supplies or if
the power transformer has been replaced. Readjustment of
the affected circuitry may be necessary . Refer to the “Per
formance Check” and “Adjustment Procedure”, Sections 4
and 5 of this manual.
DIAGNOSTIC ROUTINES
The diagnostic routines contained in the 2445 operating
firmware consist of the various power-up tests that are
automatically performed when power is first applied and
several circuit exerciser routines. The test or exerciser
routines are selected by “scrolling” through a menu of avail
able routines when the firmware is under control of the Diag
nostic Monitor. Monitor control is indicated by the message
“DIAGNSTIC. PUSH A/B TRIG TO EXIT” displayed in the
top crt graticule division.
Entry into the monitor is automatic if a power-up test
fails. The user may also force entry into the Diagnostic Mon-
6-9
Summary of Contents for 2445
Page 1: ...Tektronix 2445 OSCILLOSCOPE SERVICE INSTRUCTION MANUAL ...
Page 11: ...2445 Service 3829 01 The 2445 Oscilloscope ...
Page 44: ...Theory of Operation 2445 Service 3831 10A Figure 3 1 Block diagram ...
Page 45: ...Theory of Operation 2445 Service 3831 10B Figure 3 1 Block diagram cont 3 3 ...
Page 210: ...3829 58 Figure 9 4 2445 block diagram ...
Page 214: ......
Page 217: ......
Page 219: ...2445 382 72 ...
Page 222: ...2445 ...
Page 231: ...A 1 t C t t F t G t H t ...
Page 233: ......
Page 236: ......
Page 238: ...2445 392 1 75 ...
Page 244: ......
Page 247: ...A 1 C _____ D E F G H J 2445 3811 74 ...
Page 248: ...1 2 3 4 5 6 7 8 9 i o 2445 DISPLAY SEQUENCER TRIG GERING A4B SWEEPS ...
Page 253: ......
Page 263: ... 0 2445 J8 i S ...
Page 264: ...1 2 3 4 5 6 7 i 8 I i 9 10 2445 READOUT ...
Page 275: ......
Page 278: ......
Page 281: ......
Page 283: ... 8VJNR EG 3S 5 fROM P232 5 10 A 15VUNREG 8S F R O Mn i 2445 3 0 2 S 8 I ...
Page 286: ...2445 3823 82 ...
Page 290: ...B H le w o q 87V T S o I R v n i U1 R1873 PARTIAL A9 HIGH VOLTAGE BOARD 2445 ...
Page 299: ...2445 Service DAC REF A5 CONTROL ADJUSTMENT LOCATIONS 3 ...
Page 300: ......
Page 304: ...2 R E TU R N T O 1 ...
Page 305: ...ERROR MESSAGE DIAGNOSTICS ...
Page 306: ...ERROR MESSAGE DIAGNOSTICS ...
Page 307: ...O A A C t rnra g i tiw c t 3829 89 ...
Page 308: ...RETURN TO ...
Page 309: ...FRONT PANEL TROUBLESHOOTING ...
Page 310: ...FRONT PANEL TROUBLESHOOTING ...
Page 311: ...2445 Service 3829 90 ...
Page 316: ...R E TU R N T O v 1 y ...
Page 317: ...SWEEP TROUBLESHOOTING PROCEDURE ...
Page 323: ......
Page 324: ...2445 Service 3829 85 ...
Page 325: ......
Page 326: ... KERNEL NOP DIAGNOSTIC PROCEDURE ...
Page 327: ...10 POWER SUPPLY TROUBLESHOOTING PROCEDURE 3829 94 ...
Page 330: ......
Page 334: ...2445 Service REGULATOR TROUBLESHOOTING PROCEDURE 3829 93 ...
Page 338: ......
Page 346: ...12 2445 SERVICE ...
Page 347: ...2445 SERVICE ...
Page 348: ...2445 SERVICE ...