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HP8591E input attenuator problem

Question asked by n9llo on Apr 13, 2008
Latest reply on Jun 27, 2008 by MikeM

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I seem to have a problem with the input attenuator. The 20db section is intermittant. Sometimes I get 20db sometimes its all over the place. Sometimes it passes amplitude cal sometimes fails. The control signals are good. The unit in question is a Wavetek 0955-0453. Has anyone been inside one of these? I have the RF assembly out and on the bench, I suppose I will take the attenuator out and run some tests on it to verify the problem first.

Chris
N9LLO

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jborges3 Apr 16, 2008 12:11 PM
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Hello n9llo,

It sounds like your attenuator is faulty, I recommend you replace it instead of attempting a repair. The Agilent 8591E Service guide states that the input attenuator is not repairable at the component level and should be replaced if defective. 0955-0453 is still available from Agilent if you choose to order one.

It isn't supported, but I've heard of people repairing these assemblies if one of the pads inside is bad, however it sounds like you attenuator has a switching problem. There may be some super tech on the forum somewhere who may have some other ideas for you.

Best regards,
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ze Apr 28, 2008 7:17 PM
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I had a faulty input attenuator in a 8593, and just by running the self tests many times it started working fine again, didn''t even have to open it. Sometimes just a little exercise works. I did open a HP attenuator once and replaced half with another one and managed to close and have it still working with decent response, but it is a job to be done very slowly.

Good luck!
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Dr_joel Apr 28, 2008 10:44 PM
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"sticking" attenuators are common problem. It has two causes:

1) Lubricant sometimes gets "sticky" and acts like glue to keep the sections from moving

2) stuff gets between the contacts, and holds them open.

repeated cycling often fixes the problem. In fact, in the network analyzers, we cycle the attenuators each time we turn it on just to avoid these troubles.
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SteveReeves Jun 23, 2008 10:37 AM
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Another cause of "sticking" attenuators is seen when the metal "C" shell around a section becomes magnetized. The section will easily switch (even manually with your fingers) and tend to stick in the opposite direction.

I have found a very simple fix for this. Loosen the hex screws screws holding the C shell and slide it out. Take a piece of cellophane tape and cover the lower portion of the shell (not the underside) and carefully trim it. This prevents a direct metal-to-metal contact and thus reduce the sticking. Try it ! It's very low-tech, but also very cheap.
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MikeM Aug 21, 2014 6:44 PM
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Hi Chris,

As Joseph mentioned we don't service these attenuators at component level, they should be replaced if they are found to be defective.

While some may have replaced individual pads in other attenuators, such as the 8593 that was mentioned, the attenuator that you are working with in an 8591E is not an Agilent (or HP if older) manufactured part, it is from Wavetek as you mentioned. I also believe that these were typically soldered shut.
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HP8591E input attenuator problem

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