Agilent Technologies 46A, 45A, 54835A To troubleshoot attenuator failures, Attenuator Click Test

Chapter 5: Troubleshooting

To troubleshoot attenuator failures

To troubleshoot attenuator failures

The best method for troubleshooting attenuator assembly failures is to swap the suspected one with a known good one. This discussion will help you determine whether the attenuator or acquisition board is causing a problem.

The attenuator assembly consists of attenuators and a preamplifier for two channels. The attenuator assembly contains the following:

•A relay for selecting input resistance (50 Ω or 1 MΩ)

•Two switchable attenuators (1:1/5:1 and 1:1/10:1) which can be cascaded to provide attenuation ranges of 1:1, 5:1, 10:1, and 50:1 in the 50 Ω path

•An impedance conversion circuit in the 1 MΩ path

•A programmable preamplifier and multiplexer for 1x and 2x gain

Defective attenuators can cause a variety of symptoms.

•Wrong input resistance

•Low bandwidth/slow rise time

•Signal distortion

•Calibration failures

•Self-test failures

Firmware Calibration should also be done after attenuator replacement (see chapter 4, “Calibrating and Adjusting”).

Attenuator Click Test

The solenoids for the passive attenuators can be heard switching when the vertical sensitivity is changed. However, the gain calibration will give different switching points to different attenuator assemblies. Individual attenuator assemblies will not necessarily switch at the same sensitivities. Check for switching sounds between the following range changes:

•20 to 50 mV/div

•100 to 200 mV/div

•200 to 500 mV/div

•1.0 to 2.0 V/div

You can hear relays switching when going either direction through the transitions.

You can hear the input path relay when the input resistance is changed. Toggle the input resistance button for each channel.

If either of the click tests fail, the attenuator assembly may be defective.

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