Fluke 900 - Manual (Page 53)

FLUKE 900 SERVICE MANUAL Troubleshooting
4 Troubleshooting
4.1 Test Result Interpretation
The first step in troubleshooting is to use the poweron self test to establish a result failiue profile.
Select «prt_res» from the debug screen to diunp the detailed results to a printer coimected
to the RS232 port. The listing will consist of general results, flags and failing individual results. If
no printer is available, record the individual results as they ^pear on the display after pressing
«display» "test #" for each failing test number.
The following rules are suggested for interpreting the listed results:
RULEl:
Investigate flag failures before other failed tests. They indicate catastrophic operational failures
and cause a number of other tests to fail. The exception to this rule is when only the following
fiag(s) are present:
Interface Buffer Register ( BYTE 1 b7)
Threshold Calibration ( BYTE 3 b2)
FMASK Calibration ( BYTE 3 b3)
These flags can be caused by many things and it is usually better to begin by investigating other
failing tests first.
RULEl:
If Test 46 fails and the power supply bits of the individual result are set (bits 6,7 of BYTEl),
check the power supply voltages with a voltmeter. A problem here will cause many other failures.
If the voltages are good, then start investigating other failed tests before number 46. The
functions it exercises are complex and not easy to troubleshoot.
RULE3:
If multiple tests or multiple lines are failing, this indicates a control circuit problem. A single line
failing can be caused by a component in the signal path of that channel.
RULE 4:
When multiple tests or lines are failing, use the table that follows in this section to identify the
common circuit blocks. Refer to the theory in Section 2 to crossreference these blocks to the
board schematics. The fault can normally be isolated to the common circuitry. In addition, signal
flow diagrams at the end of this section can be of some help, since they depict the active circuitry
for a number of tests.
For example, if tests 1 and 2 pass on a certain line while tests 3 and 4 fail on the same line, the
Interface Buffer must be good, since the stimulus for tests 1 through 4 comes fiom the Buffer.
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