5 
b 
t 
4-1 
INTRODUCTION 
Section 
IV 
SECTION 
IV 
SYSTEM 
TROUBLESHOOTING 
4-2  This  section contains 
a 
diagnostic  procedure 
for determining the faulty instrument in the 3721A/ 
3720A  System  when 
a 
system  failure  occurs. 
Before troubleshooting the System,  check that the 
3721A is  functioning correctly by carrying out the 
Performance  Check  given  in  Section  Ill of  the 
3721A  Service  Manual.  Although  covering  most 
faults  likely  to  occur  in  practice,  the  System 
troubleshooting procedure 
is 
not  intended 
as 
an 
infallible method for  every  possible trouble.  For 
faults not covered here please contact your nearest 
Hewlett-Packard Service Office. Addresses are given 
at 
the back of this manual. 
4-3 
USING TROUBLESHOOTING SECTION 
4-4  Paragraph  4-12  gives  the  settings  for  the 
controls on the 3721A and 3720A required before 
starting to troubleshoot the System. Except where 
indicated  in the  appropriate Flow, these  settings 
should be maintained throughout the troubleshoot- 
ing procedure. 
4-5  When  there 
is 
a 
fault  in the System  and the 
problem area is unknown, start 
at 
Flow A and work 
through to Flow D to isolate the faulty instrument. 
When  the  problem  area  is  known  refer  to  the 
appropriate  Flow. Table 4-1 
lists 
the Flow charts. 
Table 4-1 
Flow 
charts 
Flow 
Problem Area 
A  Control faults 
B 
Display Sensitivity faults 
C 
Data Transfer faults 
D  Other Transferred Signals faults 
NOTE: 
When  there 
is 
a 
fault in the System and 
it 
occurs 
only 
when  displaying  Modulus,  Log Mod 
and/or  Phase,  then  the  fault 
is 
in  the  3720A. 
4-6  When  carrying  out  System  troubleshooting 
the rear panel connector wiring details are available 
for reference in Section 
V 
of this manual. 
4-7  Once  the fault  has  been  localised to one  of 
the instruments refer to Table 4-2 for the approp- 
riate action to be taken. 
Table 4-2  3721 A/3720A 
System 
repair procedure 
Faulty 
Instrument 
Action 
3721A Correlator 
1554914 Interface Accessory 
(Assembly and Cable) 
3720A Spectrum Display 
Refer to 3721A Service Manual 
Refer to 15549A Operating and Service Manual 
Return 3720A to your nearest Hewlett-Packard Service 
Office for repair 
4- 
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