HP 3457A Service Manual page 201

8-72. General Information
Other than the normal operating configurations, this DMM provides three special configurations. These
are the Self Test, Diagnostic and Autocal modes.
The Self Test mode is designed to provide confidence testing of the instrument. It is a progressive test
of both analog and digital hardware that gives better than 90% confidence of proper hardware opera-
tion. Through interpretation of the self test failure results, most instrument failures can be isolated to
small functional blocks where more traditional troubleshooting techniques can be used to isolate the
failed component.
Diagnostic operation is a subset of self test operation. There are two internal mechanical adjustments
performed by using diagnostics called Diagnostic 4 and Diagnostic 8. Diagnostic 4 is discussed in the
Input Amplifier Offset Adjustment procedure in section 5 and Diagnostic 8 is discussed in the AC
Convertor Frequency Response Adjustment procedure. There are also 3 other diagnostics that are sub-
sets of self tests 1, 2 and 3. They will be discussed in the Self Test paragraphs in this section.
In the Autocal (ACAL) mode, two 10 bit D to A Converters (DAC's) are used in the DMM for correc-
tion of instrument error sources, One DAC is general purpose and is used to supply DC correction vol-
tages to various circuits. The other DAC performs the specialized function of high frequency compen-
sation of the two AC input attenuator circuits. There are six different correction constants generated
when a full Autocal (ACAL) is executed. Three DC constants are produced along with two AC at-
tenuator correction constants. In addition, the internal 10M ohm divider is measured for future use
during ohms measurements above 30M ohms.
8-73. A1 Assembly Failure Indications
If the front panel display remains blank or contains some unintelligible messages and appears to be
"locked up" after the instrument is "turned on", the fault is probably located on the Al assembly
(03457-66501). For this condition, refer to the Self Test information in this section (especially tests 0, |
and 2). If the display is blank, the power cord, fuse and line select switches should be checked to be
certain the instrument is receiving power. Connectors Al-J501, Al-J701 and Al-J702 should be checked
to be sure they are properly and securely connected. If you have a 03457-66511 assembly, refer to sec
tion 8-78 for more information.
If the instrument works properly from the front panel but fails to communicate over the HP-IB. the
problem is due to a faulty Al assembly. Be certain the interface cable is good and that it is securely
connected between the HP 3457A and the controller when testing HP-IB communications.
If the display reads FAILED after the instrument is "turned on" or after a self test, refer to the Self Test
information in this section.
8-74, A2/A3 Assembly Failure Indications
Failures in these assemblies can usually be detected by running the TEST routine. A failure will be in-
dicated by a display of TEST FAILED and the error annunciator flashing. If this occurs, refer to the
Self Test information in this section.
8-75. Self Tests
There are two categories of self tests that can be performed on the DMM assembly. These are the
power-on self test and a keyboard executable self test. When power is applied, a Power-on Self Test is
performed. The Power-on Self Test is an abbreviated version of the Self Test executed with the TEST
command.
HP 3457A Multimeter
8-36