Tektronix 422, Instruction Manual

Page: 71 / 213

Maintenance—Type 422 AC-DC
checking transistor operation are given under Trouble­
shooting.
Recalibration
To assure accurate measurements, check the calibration
o f this instrument after each 1000 hours of operation or
every six months if used infrequently. In addition, replace­
ment of components may necessitate recalibration o f the
affected circuits. Complete calibration instructions are
given in the Calibration section.
The calibration procedure can also be helpful in local­
izing certain troubles in the instrument. In some cases,
minor troubles may be revealed and/or corrected by recali­
bration.
TROUBLESHOOTING
Introduction
The following information is provided to facilitate
troubleshooting of the Type 422. Inform ation contained in
other sections should be used along w ith the following
information to aid in locating the defective component. An
understanding of the circuit operation is very helpful in
locating troubles. See the Circuit Description section fo r
complete information.
Troubleshooting Aids
Diagrams. Complete circuit diagrams are given on fold-
out pages in the Diagrams section. The component number
and electrical value o f each component in this instrument
are shown on the diagrams. Each main circuit is assigned a
series of component numbers. Table 4-1 lists the main
circuits in the Type 422 and the series of component
numbers assigned to each. Im portant voltages and wave­
forms are also shown on the digrams. The portions o f the
circuit mounted on circuit boards are enclosed with a blue
line.
TABLE 4-1
Component Numbers
Component numbers
on diagrams
Diagram
number
Circuit
1-99 1 Channel 1 Input Am plifier
100-199 2 Channel 2 Input Am plifier
200-299
4
Vertical Switching and
Output Am plifier
300-399 5 Sweep Trigger
400-499 6 Sweep Generator
500-599 8 horizontal Am plifier
700-799 9 Calibrator and Regulators
800-899 10 CRT C ircuit
1000-1099 11 AC-DC Power Selector
1100-1299 12 DC-DC Regulator
Switch Wafer Identification. Switch wafers shown on
the diagrams are coded to indicate the position o f the wafer
in the complete switch assembly. The numbered portion of
the code refers to the wafer number counting from the
fro n t, or mounting end o f the switch, toward the rear. The
letters F and R indicate whether the fro n t or rear o f the
wafer performs the particular switching function. For
example, a wafer designated 2R indicates that the rear of
the second wafer from the fro n t is used fo r this particular
switching function.
Circuit Boards. Figs. 4-8 through 4-17 show the circuit
boards used in the Type 422. Fig. 4-7 shows the location of
each board w ithin the instrument. Each electrical compo­
nent on the boards is identified by its circuit number. The
circuit boards are also outlined on the diagrams w ith a blue
line. These pictures, used along w ith the diagrams, aid in
locating the components mounted on the circuit boards.
Wiring Color-Code. A ll insulated wire and cable used in
the Type 422 is color-coded to facilitate circuit tracing.
Signal carrying leads are identified w ith one or tw o colored
stripes. Voltage supply leads are identified w ith three
stripes to indicate the approximate voltage using the EIA
resistor color-code. A white background color indicates a
positive voltage and a tan background indicates a negative
voltage. The widest color stripe identifies the firs t color of
the code. Table 4-2 gives the wiring color-code fo r the
power-supply voltages used in the Type 422.
TABLE 4-2
Power Supply Wiring Color Code
Supply Background
color
First
stripe
Second
stripe
Third
stripe
—110 volt Tan
Brown Black Brown
—81 volt Tan Gray
Black Black
- 1 2 volt
Tan Brown Red
Black
+10.5 volt White
Violet Green Black
+12 volt White
Brown Red
Black
+55 volt White
Green Green Black
+95 volt White
Brown Black Brown
Resistor Color-Code. In addition to the brown composi­
tion resistors, some metal-film resistors and some wire-
wound resistors are used in the Type 422. The resistance
values of wire-wound resistors are printed on the body of
the component. The resistance values o f composition resis­
tors and metal-film resistors are color-coded on the compo­
nents w ith EIA color-code (some metal-film resistors may
have the value printed on the body). The color-code is read
starting w ith the stripe nearest the end of the resistor. Com­
position resistors have four stripes which consist of tw o
significant figures, a m ultiplier and a tolerance value (see
Fig. 4-2). Metal-film resistors have five stripes consisting of
three significant figures, a m ultiplier and a tolerance value.
Capacitor Marking. The capacitance values o f common
disc capacitors and small electrolytics are marked in micro-
El 4-3