Tektronix 1L20, Инструкция по эксплуатации

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Maintenance— Type 1L20
Check Instrumentation Calibration. Check the calibra­
tion o f the instrument, or the affected circuit if the trouble
exists in one circuit. The indicated trouble may only be a
result of misadjustment or may be corrected by recalibra­
tion.
Complete instructions are given in the Calibration
section of this manual. Individual calibration steps can be
performed out of sequence in some cases. However, if the
circuit affects the calibration of other circuits in the instru­
ment or if several controls are interacting, a more complete
calibration w ill be necessary. Before you change any set­
tings during this check, note the settings so that you can
return the controls to their original positions. This will often
make recalibration much easier.
Isolate the Trouble to a Part of the Instrument.
Although some troubles may disrupt the operation of the
entire instrument, most troubles w ill affect the operation
of ONLY ONE AREA or CIRCUIT.
Visual Check. Visually check the circuit in which the
trouble is located. Many troubles can be located by visual
indications such as unsoldered connections, broken wires,
damaged components, etc.
Check Voltages and Waveforms. Often the defective
component can be located by checking for the correct volt­
ages or waveforms in the circuit. Typical voltages and
waveforms are given in the Schematic Diagrams.
NOTE
V oltages and w aveform s given on the diagram s
are not absolute and m ay v a ry s lig h tly between
instruments. To o b ta in o p e ra tin g conditions simi­
la r to those used to ta ke these readings, see the
firs t page o f the schematics.
Most voltage measurements can be taken with a 20,000
ohms/volt DC voltmeter, but do not use a low-volts range on
a high impedance circuit. Use a higher range or an oscillo­
scope w ithin X 1 0 probe. Accuracy o f the voltmeter should
be w ithin 3% on all ranges. Be sure that the test probes are
well insulated to prevent accidental shorting of the compo­
nents.
For checking waveforms, use a test oscilloscope which
has the following minimum specifications:
Bandwidth: DC to 10 MHz.
Deflection Factor: 0.05 Volts/division.
Input Impedance: lO M fi paralleled by l OpF when using
a 1 0 X probe.
Connections to the IF Chassis and to the Phase-Lock
are made through square-pin connectors and clips. These
connectors make convenient test points for troubleshooting,
since much of the circuitry connected to them is inaccessible
without disassembly of the instrument.
Tables 4-4, 4-5 and 4-6 list the DC resistance between the
various pins and ground, first with the cable-clips connected
to the pins, and then with all the clips disconnected. The
tables also list the resistance between the pins of P ll (the
rear-plate connector) and ground.
The color code o f the wires soldered to the clips is the
same as the color code of the wires soldered to the pins
except as noted; if the clips are disconnected, be sure that
they are
a ll reconnected properly before the power is
applied.
The resistance measurements may vary considerably.
Because o f the semiconductors used in the circuitry, the
ohmmeter readings will be affected by the biasing supplied
by the internal voltages of the meter. Since ohmmeters d if­
fer in the internal voltage used on each range and in the
currents required for deflection, the readings can vary as
much as 50% between different types of meters, even when
using the same range. For future reference, empty columns
are provided in each table for logging your own measure­
ments and the type of meter used.
TABLE 4 -4
Phase Lock Square-Pin Connectors
Meter
Resistance in Ohms1
Pin C able Connected
C able Disconnected
(Reversed P o la rity)
(Reversed P o la rity )
A 0 0
0 0
B 2.7 k fi 9.5 kfi
4.4 k fi 16 k fi
C 5.6 k fi 5.4 k fi
lO M fi lO M fi
(brown)
D 65 k fi 85 k fi
oo
00
(yellow)
E 70 k fi 85 k fi
00 00
F 4.5 k fi 3.4 k fi
25 k fi 6.5 k fi
G 2 k fi 1.9 k fi 00 oo
H
5.4 kfi
5.6 k fi
60 k fi 150 k fi
1 NC NC
J NC
NC
4 -7