Tektronix 2246 1Y, Service Manual

Page: 144 / 433

Maintenance—2246 1Y and 2246 Mod A Service
TROUBLESHOOTING
INTRODUCTION
Preventive maintenance performed on a regular
basis should reveal most potential problems before
an
instrument malfunctions. However, should
troubleshooting be required, the following infor­
mation is provided to aid in locating a fault. In
addition, the material presented in the Theory of
Operation and Diagrams sections of this manual may
be helpful while troubleshooting.
TROUBLESHOOTING AIDS
Diagnostic Firmware
This instrument contains built-in diagnostic routines
that can aid in localizing failures. An automatic
power-up self test checks the system RAM and ROM
and readout interface circuitry. If a failure is
detected, this information is presented in either of
two ways: a flashing code display on the Trigger
LEDs or, if the instrument is capable of presenting a
readout, error messages in the crt display. In
addition to the power-on testing, various diagnostic
routines can be run from the service mode using the
SERVICE MENU. (See Internal Testing Capabilities in
this subsection for the details.)
Schematic Diagrams
Complete schematic diagrams are located on
tabbed foldout pages in the Diagrams section.
Portions of circuitry mounted on each circuit board
are enclosed by heavy black lines. The assembly
number and name(s) of the circuit(s) are shown
near the top or the bottom edge of each diagram.
Functional blocks on schematic diagrams are out­
lined with a wide gray line. Components within the
outlined area perform the function designated by the
block label. The Theory of Operation uses these
functional block names when describing circuit
operation as an aid in cross-referencing between
the circuit description and the schematic diagrams.
Component numbers and electrical values of com ­
ponents in this instrument are shown on the sche­
matic diagrams. Refer to the first page of the
Diagrams section for the reference designators and
symbols used to identify components. Important
voltages and waveform reference numbers
(enclosed in hexagonal-shaped boxes) are also
shown on each diagram. Waveform illustrations are
located adjacent to their respective schematic
diagram.
Circuit Board Illustrations
Circuit board illustrations showing the physical lo­
cation of each component are provided for use in
conjunction with each schematic diagram. Each
board illustration is found in the Diagrams section on
the back of a foldout page, preceding the first
related schematic diagram (s).
The locations of waveform test points are marked on
the circuit board illustrations with hexagonal outlined
numbers corresponding to the waveform numbers
on both the schematic diagram and the waveform
illustrations.
Circuit Board Locations
The location of a circuit board within the instrument
is shown on each foldout page along with the circuit
board illustration.
Circuit Board Interconnections
A circuit board interconnection diagram (schematic
Diagram 16) is provided in the Diagrams section to
aid in tracing a signal path or power source between
boards. All wire, plug, and jack numbers are shown
along with their associated wire or pin numbers and
signal names.
Power Distribution
Two Power Distribution diagrams (schematic
Diagrams 14 and 15) are provided to aid in trouble­
shooting power supply problems. These diagrams
show the components that the various voltages are
applied to and the jum per connections and de­
coupling components used to apply the power to
those circuits. Excessive loading on a power supply
by a circuit fault may be isolated by disconnecting
the appropriate jumpers.
Grid Coordinate System
Each schematic diagram and circuit board illus­
tration has a grid border along its left and top edges.
A table located next to each schematic diagram lists
the grid coordinates of each component shown in
that diagram. To aid in physically locating
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