Service manual

Signature Analysis

Note: You cannot use signature analysis to troubleshoot units with the following serial numbers:

Agilent 6050A: 3714A05433 and up; US37140101 and up.

Agilent 6051A: 3714A00711 and up; US37140101 and up.

The easiest and most efficient method of troubleshooting microprocessor based instruments is signature analysis (SA). The

SA technique is similar to signal tracing with an oscilloscope in linear circuits. Part of the microcomputer memory is

dedicated to signature analysis and a known bit stream is generated to stimulate as many nodes as possible within the circuit.

However, because it is virtually impossible to analyze a bit stream with an oscilloscope, a signature analyzer is used to

compress the bit stream into a four character signature. By comparing signatures of the IC under test to the correct

signatures for each node, faults can usually be isolated to one or two components.

Signature analysis tests are provided for most of the digital circuits in the primary and secondary circuits of the Electronic

Load. There are six primary SA tests given in Tables 3-4 through 3-9, and five secondary tests given in Tables 3-10 through

3-14. Refer to "Firmware Revisions" for information about the valid firmware revisions for the signature analysis tables.

References are made to the appropriate SA test table from the troubleshooting flow charts or procedures. The following

general rules apply to signature analysis testing of the primary and secondary circuits.

1. Be sure to use the correct test setup connections for the specific test. See "Test Setup for Signature Analysis".

2. Note the signatures for Vcc ( + 5V) and common on the IC being examined. If an incorrect signature is the same as that

of Vcc or common, that pin (or point in the circuit) is probably shorted to Vcc or ground.

3. If two pins have identical signatures, they are probably shorted together.

4. If two signatures are similar, it is only a coincidence.

5. If a signature is incorrect at an input pin, but is correct at its source (output of previous IC), check for printed circuit

track or soldering problems.

6. An incorrect signature at an output could be caused by a faulty component producing the output. It can also be caused

by an input short circuit in another component on the board.

Firmware Revisions

The primary ROM chip (U205) and the secondary microprocessor chip (U301) are identified with labels that specify the

revision of the Electronic Load's firmware.

The signatures given in Primary SA Tables 3-4 through 3-9 are valid for ROM chip U205 firmware revision "Rev A.01.01''.

You can also identify the revision of the U205 firmware using the *IDN? query in the program listed below.

10 DIM L$[40]

20 OUTPUT 705;"*IDN?"

30 ENTER 705; L$

40 DISP L$

50 END

The computer will display the Electronic Load mainframe's model number and the firmware revision of the U205 primary

ROM chip: ''Agilent-Technologies, 6050A, 0,A.01.01".

The signatures given in Secondary SA Tables 3-10 through 3-14 are valid for secondary microprocessor chip U301 revision

"Rev A.02.01" . Note that the U301 revision is only identified by the label; it cannot be read back using the *IDN? query.