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8640B won't switch to highest +20 dBm range

 

I just purchased a pretty clean 8640B signal generator, but it has a couple of little problems. I already fixed a loose set screw down inside on the option 001 variable audio oscillator and will be adjusting and calibrating the audio oscillator tomorrow.
?
It also has an 003 option and 2232A serial prefix.
?
But I am having a problem with the RF output step attenuator where it won't switch to the highest +20 dBm range, but will switch 1 step below the lowest -130 dBm setting, though that causes the output meter level to drop to zero.?
?
The upper ranges check as perfectly calibrated to a fairly new digital oscilloscope and within a dB or so to a TinySA ULTRA spectrum analyzer. It appears that someone has had the attenuator housing open as evidenced buy an original HP paper sticker that has been sliced along a seam.
?
It seems an odd situation, but does anyone have an idea what is going on? Unless I get a better clue, I plan to pull the attenuator out and open it up tomorrow.?
?
Thanks
 

Here is a weird idea: Has the power amp been bypassed or partly failed? I have worked on a few of these and never saw this. When you say wont switch: is the attenuator knob not set right, not sure I understand.? J. Kruth

In a message dated 7/15/2024 7:28:59 PM Eastern Standard Time, david.hostetler@... writes:
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I just purchased a pretty clean 8640B signal generator, but it has a couple of little problems. I already fixed a loose set screw down inside on the option 001 variable audio oscillator and will be adjusting and calibrating the audio oscillator tomorrow.
?
It also has an 003 option and 2232A serial prefix.
?
But I am having a problem with the RF output step attenuator where it won't switch to the highest +20 dBm range, but will switch 1 step below the lowest -130 dBm setting, though that causes the output meter level to drop to zero.?
?
The upper ranges check as perfectly calibrated to a fairly new digital oscilloscope and within a dB or so to a TinySA ULTRA spectrum analyzer. It appears that someone has had the attenuator housing open as evidenced buy an original HP paper sticker that has been sliced along a seam.
?
It seems an odd situation, but does anyone have an idea what is going on? Unless I get a better clue, I plan to pull the attenuator out and open it up tomorrow.?
?
Thanks
 

Hi:
You can test the attenuator within the instrument. you can connect a SMA cable to attenuator input, check the level at N output connector .

Test the attenuation correct or not. + 20dBm had a switch control to the final AMP circuit, check the service manual.

Regard
Tony Cheung
JUL 16 2024
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On Tuesday, July 16, 2024 at 07:28:59 AM GMT+8, Dave W6OQ via groups.io <david.hostetler@...> wrote:


I just purchased a pretty clean 8640B signal generator, but it has a couple of little problems. I already fixed a loose set screw down inside on the option 001 variable audio oscillator and will be adjusting and calibrating the audio oscillator tomorrow.
?
It also has an 003 option and 2232A serial prefix.
?
But I am having a problem with the RF output step attenuator where it won't switch to the highest +20 dBm range, but will switch 1 step below the lowest -130 dBm setting, though that causes the output meter level to drop to zero.?
?
The upper ranges check as perfectly calibrated to a fairly new digital oscilloscope and within a dB or so to a TinySA ULTRA spectrum analyzer. It appears that someone has had the attenuator housing open as evidenced buy an original HP paper sticker that has been sliced along a seam.
?
It seems an odd situation, but does anyone have an idea what is going on? Unless I get a better clue, I plan to pull the attenuator out and open it up tomorrow.?
?
Thanks
 

?
I had a problem on mine many years ago and found a bad reed relay, though my
problem had to do with switching between the high and low halves of the frequency
bands. There is a board with a bunch of reed relays rather deep inside, and I
wonder if they also used some of them for switching attenuator ranges. Might
be worth checking the schematic and see if there are any on the attenuator pages.
?
John K0GCJ
 

Hello Dave,
Your diagnosis suggests the attenuator knob and switch is out by one detent.
73 de Brian, VK2GCE


----- Original Message -----

To:
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Sent:
Mon, 15 Jul 2024 15:48:36 -0700
Subject:
[HP-Agilent-Keysight-equipment] 8640B won't switch to highest +20 dBm range


I just purchased a pretty clean 8640B signal generator, but it has a couple of little problems. I already fixed a loose set screw down inside on the option 001 variable audio oscillator and will be adjusting and calibrating the audio oscillator tomorrow.
?
It also has an 003 option and 2232A serial prefix.
?
But I am having a problem with the RF output step attenuator where it won't switch to the highest +20 dBm range, but will switch 1 step below the lowest -130 dBm setting, though that causes the output meter level to drop to zero.?
?
The upper ranges check as perfectly calibrated to a fairly new digital oscilloscope and within a dB or so to a TinySA ULTRA spectrum analyzer. It appears that someone has had the attenuator housing open as evidenced buy an original HP paper sticker that has been sliced along a seam.
?
It seems an odd situation, but does anyone have an idea what is going on? Unless I get a better clue, I plan to pull the attenuator out and open it up tomorrow.?
?
Thanks
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