Troubleshooting; Troubleshooting Aids; Troubleshooting Equipment; Troubleshooting Techniques - Tektronix 7B51 Instruction Manual

Maintenance-Type 7851
TROUBL ESHOOTI NG
Introduction
The following information is provided to facilitate
troubleshooting of the Type 7851. Information contained
in other sections of this manual should be used along with
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 Descrip-
tion section for complete information.
Troubleshooting Aids
Diagrams. Circuit diagrams are given on foldout pages in
Section 8. The component number and electrical value of
each component in this instrument are shown on the dia-
grams. Important voltages and waveforms are also shown on
the diagrams.
Switch Cam Identification. Switch cam numbers shown
on the diagrams indicate the position of the cam in the
complete switch assembly. The cams are numbered from
the front, or mounting end of the switch, toward the rear.
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 7851. The resistance
values of wire-wound resistors are printed on the body of
the component. The resistance values of composition resis-
tors and metal-film resistors are color-coded on the com-
ponents (some metal-film resistors may have the value
printed on the body) with EIA color code. The color code
is read starting with the stripe nearest the end of the resis-
tor. Composition resistors have four stripes which consist of
two significant figures, a multiplier and a tolerance value
(see Fig. 4-1). Metal-film resistors have five stripes consis-
ting of three significant figures, a multiplier and a tolerance
value.
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 ce-
ramic capacitors used in the Type 7851 are color coded in
picofarads usi ng a modified E I A code (see Fig. 4-1 ).
Diode Color Code. The cathode end of each glass-
encased diode is indicated by a stripe, a series of stripes or a
dot. For most silicon or germanium diodes with a series of
stripes, the color code also indicates the type of diode or
identifies the Tektronix Part Number using the resistor
color code system (e.g., a diode color-coded blue- or pink-
brown-gray-green indicates Tektronix Part Number
152-0185-00). The cathode and anode ends of metal-
encased diodes can be identified by the diode symbol
marked on the body.
4-2
Troubleshooting Equipment
The following equipment is useful for troubleshooting
the Type 7851:
1. Transistor Tester
Description: Tektronix Type 576 Transistor-Curve
Tracer or equivalent.
Purpose: To test the semiconductors used in this in-
strument.
2. Volt-ohmmeter
Description: 20,000 ohms/volt. 0-500 volts DC.
Accurate within 3%. Test probes must be well insulated.
Purpose: To measure voltages and resistances.
3. Test Oscilloscope
Description: DC to 100 MHz frequency response, 5
millivolts to 5 volts/division deflection factor. Use a lOX
probe.
Purpose: To check waveforms in the instrument.
4. Plug-In Extender
Description: Rigid plug-in extender, Tektronix Part
number 067-0589-00.
Purpose: Permits operation of the unit outside the
plug-in compartment for better accessibility during
troubleshooting.
Troubleshooting Techniques
This troubleshooting procedure is arranged in an order
which checks the simple trouble possibilities before pro-
ceeding with extensive troubleshooting. The first few
checks ensure proper connection, 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 fol-
lowing the replacement procedures given under Corrective
Maintenance.
1. Check Control Settings. Incorrect control settings
can indicate a trouble that does not exist. If there is any
question aboU1: the correct function or operation of any
control, see the Operating Instructions section.
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