Swapping Attenuators; Attenuator Connectivity Test - Agilent Technologies 54835A Service Manual

Swapping Attenuators

Attenuator swapping is the best method of finding a faulty attenuator. All input channels of the
Infiniium oscilloscope use identical attenuator assemblies. The attenuators for channels 1/2 and
3/4 have been manufactured into assemblies to enhance sampling performance. This
troubleshooting method provides fast trouble isolation because it is unlikely that multiple
channels will experience the same attenuator failure.
Swap suspected and good attenuators, and rerun the tests. The good attenuator can be a
separate, known good part, or the attenuator assembly for the other channels of the oscilloscope.
If the swap test reveals a faulty attenuator assembly, then install a new attenuator assembly to
replace the faulty one, and return the swapped attenuator assembly to its original channels.
Following this procedure will maintain the integrity of the attenuator actuation counters.
The attenuator actuation counter is maintained by the oscilloscope software to keep track of the
number of times an individual attenuator has switched. Each attenuator is capable of 2 million
or more actuations (switches of contacts) before the reliability of the contacts begins to degrade.
This provides useful preventative maintenance information for keeping the Infiniium oscilloscope
in peak measurement condition. If you replace or permanently swap an attenuator, you may need
to reset the attenuator counter. See "To reset the attenuator contact counter" on page 6-30.

Attenuator Connectivity Test

The attenuator assembly scales incoming signals so that the acquisition system can accurately
digitize the signal. The Click Test verifies that the relays for switching input resistance and the
passive attenuators are working. This connectivity test provides a qualitative assessment of
attenuator operation.
Connect the Aux Out signal from the front panel to the Channel 1 input using a 50 Ω
1
BNC cable.
Press the Default Setup key, then the Autoscale key.
2
The connected channel should display the 715 Hz square wave of the Aux Out signal
3
in both the 50 Ω and 1 M Ω path. If the waveform is not found, or is not stable horizontally
and vertically, the attenuator's internal connectivity is suspect. Swap the attenuator
assembly with a new or known good assembly (see "Swapping Attenuators").
Repeat steps 1 through 3 for the remaining input channels.
4
If swapping attenuators into malfunctioning channels does not correct the problem, perform the
procedure in "To run the self-calibration" in chapter 4. Then repeat the above procedure for the
malfunctioning channels.
Chapter 5: Troubleshooting
To troubleshoot attenuator failures
5–57