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Service
Model 8901B
Catastrophic Failures
Begin troubleshooting catastrophic failures by performing the troubleshooting checks on Service Sheet
BD1. The simple procedures there
take
only a few minutes and will quickly differentiate a control
(digital) problem from a hardware (analog) problem. The checks give cross-references to the detailed
block diagrams (Service Sheets BD2 to BD5) which then direct you to the necessary schematic.
The troubleshooting information found on all service sheets consists of a series of performance checks.
The purpose of the checks is not to identify which circuit or component has failed but rather to verify
whether the assembly or circuit
is
operating correctly. Information on the possible cause of failure is
given in the form of hints whenever they can be given reliably. The limits given in the troubleshooting
checks are rather loose to facilitate the use of general-purpose equipment (usually an oscilloscope). If
a slightly out-of-tolerance condition is suspected, the test can usually be run more rigorously paying
greater attention to measurement accuracy.
Troubleshooting on the block diagram level normally utilizes User and Service Special h c t i o n s , while
troubleshooting on the schematic level often utilizes Direct Control Special Functions. Direct Control
Special F'unctions will require some study of their operation before using them for the first time.
8A-6
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