Troubleshooting Techniques - Tektronix 2A61 Instruction Manual

Maintenance—Type 2A61
Wiring Color Code. All insulated wire used in the Type
2A6l is color-coded according to the E{A standard color code
(as used for resistors) to facilitate circuit tracing. The widest
color stripe identifies the first color of the code. Power sup-
ply voltages can be identified by three color stripes and
the following background color code: white, positive voltage;
tan, negative voltage. Table 4-1 shows the wiring color code
for the power supply voltages used in the Type 2A61. The
remainder of the wiring in the Type 2A61 is color coded with
two or less stripes or has a solid background with no stripes.
The color coding helps to trace a wire from one point in the
instrument to another.
TABLE 4-1
Background Ist 2nd 3rd
Supply Color Stripe Stripe Stripe
—100 Tan Brown Black Brown
—12.2 Tan Brown Red Black
+125 White Brown Red Brown
+300 White Orange | Brown Brown
6.3 VAC White Blue Brown
Resistor Color Code. A number of precision metal film
resistors are used in this instrument. These resistors can be
identified by their gray body color. If a metal film resistor
has a value indicated by three significant figures and a
multiplier, it will be color coded according to the EIA stand-
ard resistor color code. If it has a value indicated by four
significant figures and a multiplier, the value will be printed
on the body of the resistor. For example, a 333 kQ resistor
will be color coded, but a 333.5kQ resistor will have its
value printed on the resistor body. The color code sequence
is shown in Fig. 4-2.
Composition resistors are color coded according to the
EIA standard resistor color code.
Capacitor Marking. The capacitance values of common
disc capacitors and small electrolytics are marked in micro-
farads on the side of the component body. The white ceramic
capacitors used in the Type 2A61 are color coded in pico-
farads using a modified EIA code (see Fig. 4-2).
Troubleshooting Techniques
This troubleshooting procedure is arranged in an order
which checks the simple trouble possibilities before proceed-
ing with extensive troubleshooting. The first few checks
assure proper connections, operation and calibration. If the
trouble is not located by these checks, the remaining steps
aid in locating the defective component. When the defective
component is located, it should be replaced following the
replacement procedure given in this section.
1, Check the Associated equipment. Before proceeding
with troubleshooting of the Type 2A61, check that the equip-
ment used with it is operating correctly. Check that the sig-
nal is properly connected and that the interconnecting cables
or probes are not defective.
2. Check Control Settings. Incorrect settings of the con-
trols on the Time Base Plug-in, the 560 Series Indicator or
the Type 2A61 can indicate a trouble that does not exist.
For example, an incorrect setting of the Time/div Variable
control on the Time Base Plug-in will give erroneous risetime
4-4
measurements; incorrect settings of the mV/div and/or Vari-
able appears as incorrect gain; incorrect setting of the trig-
gering controls on the Time Base Plug-in might appear to be
defective trigger pickoff, etc.
If there is any question about the operation or correct
function of any control, consult the Operating Instructions
section of the manual for the instrument involved.
3. Check Instrument Calibration. Check the calibration
of 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 calibration. Complete
instructions are given in the Calibration section of this manual.
Individual calibration steps can be performed out of sequence.
However, if the circuit affects the calibration of other circuits
in the instrument, a more complete calibration will be nec-
essary. General Information in the Calibration section
describes how steps which interact are noted.
4. 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 or
damaged components.
5. Check Resistances to Ground. Check the resistance
to ground on each of the pins on the Amphenol 24 pin con-
nector, Fig. 4-3. Table 4-2 shows pin numbers, approximate
resistance which should be seen and the use of each pin.
TABLE 4-2
Pin No. Approx Resistance Use
1 19 6.3 volts, AC
2 0 6.3 volts, AC
3,4 Inf Unused
5 0 Ground
6,78 Inf Unused
9 0 Ground
10 50 kQ +300 volts
11 40 ko Trigger Out
12 Inf Unused
13,14,15 30 kQ +125 volts
16 49 —12.2 volts
17 ; 50 ka Output
18,19,20 Inf Unused
21 50 ka Output
22 1kQ —100 volts {unreg)
23 10 kQ —100 volts (reg)
24 0 Gnd
NOTE
The DC resistance of any circuit is dependent on
several factors. Therefore, the resistances in the
table are approximations and not to be con-
sidered absolute values.
6. Check Voltages and Waveforms. Often the defective
component can be located by checking for the correct voltage
or waveform in the circuit. Typical voltages are given on
the Schematic Diagrams. To check waveforms apply a signal
to the input and trace the signal through the amplifiers. Any
waveform distortion or loss of signal is an indication of the
location of the trouble.