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Model 3580A
Section VII
SECTION VII
TROUBLESHOOTING AND
CIRCUIT
7-1. INTRODUCTION.
7-2. This section of the manual contains troubleshooting
information and circuit diagrams for the Model 3580A
Spectrum Analyzer. Included are troubleshooting informa-
tion, information on factory selected components, func-
tional block diagrams, schematic diagrams and component
location diagrams.
7-3. TROUBLESHOOTING AND PREVENTIVE MAIN-
TENANCE.
7-4. General Troubleshooting Procedures.
7-5. Troubleshooting information for the 3580A can be
found in the functional block diagrams and circuit diagrams
at the end of Section VII. An extensive set of notes,
waveforms, and tables has been provided to help narrow the
problems down from the functional block, to a board, and
finally to a component.
7-6. Use the Overall Functional Block Diagram (Figure 7-1)
to narrow the 3580A problem down into one of the four
major functional blocks:
1) Input Section
2) Frequency and Sweep Section
3) IF Section
4) Display Section.
lhis diagram gives a good overall look at the 3580A
operation. Once the diagram is understood, the failure
symptoms alone may be adequate to lead you to the proper
block. Other times, the output signals from the 3580A will
suffice. For instance, the RECORDER X-AXIS and Y-AXIS
outputs give an indication of proper instrument operation
up to, but not including, the A7 Logic Board. The
TRACKING OSC OUTPUT indicates if the Frequency and
Sweep Section is working properly.
7-7. If the external control signals and front panel failure
symptoms are not adequate to localize a problem to a
particular block, remove the 3580A outer covers and check
the appropriate input and output lines of each block. This
will localize the problem to a block. The Analog Block
Diagram (Figure 7-2), circuit schematics and associated
notes can then be used to isolate the problem to the
component.
DIAGRAMS
7-8. A2 Board VTO Troubleshooting.
7-9. The A2 VTO is part of a complex feedback loop.
If
the VTO circuitry is not working properly, the feedback
loop can be broken by applying approximately - 1.6 V de
to A2TP4. A 0 to
+
9 V de signal supplied to the VTO
ERROR AMP on the RED jumper lead to the A2 board
should then cause the oscillator frequency to vary from 1.0
to 1.5 MHz (Oto 50 kHz Input Frequency). This signal can
then be followed around the feedback loop to find the
faulty components. Use the waveforms supplied with the
A2 board to aid in this process.
7-1 0. AJ Board T rou blesho oti ng.
7-11. This part of Section VII contains test procedures for
the digital control circuitry of the A3 Sweep Board
(Schematic 4).
If
the previous troubleshooting procedures
indicate problems with the normal or adaptive sweep
circuitry, perform these test procedures.
a. Position the 3580A front panel controls to:
SWEEP MODE ..................... REP
Short A3TP1 to the gray jumper wire connected near the
center of the A3 board (Don't remove the gray jumper).
b. Adjust A3R54 (INTEGRATOR BALANCE) to verify
that the output of the Ramp Integrator (A3TP1) can be
adjusted from a positive to negative de voltage. Readjust
A3R54 for 0.000 volts
±
.001 volts.
c. Measure Vsg on the dual FET, A3QI. Both FET's
should have Vsg ..;;; 3 V de.
d. Set switch SI to the test position (UP position).
Verify that CLOCK OUTPUT (A3U8 pin 11) is a TTL
HIGH(;;;. 2.0 V de). Return SI to the normal position.
e. Remove the clock test jumper between Q18 and SI.
Reposition:
SWEEP MODE ................... RESET
f. Connect a logic clip to A3U5. Turn the 3580A
POWER switch OFF then back to ON. The instrument
CBA
should come up in state 000 or 100, where the C, B, and A
state outputs are located on pins 13, 14 and 15 respectively
of A3U5.
If
the instrument comes up in state 000, clock it
to state 100 by momentarily switching A3Sl into, and then
out of the test position. (This process will be called
"clocking Sl" from now on.)
7-1
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