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DIY: Repair of HP Step Attenuators

 

Here’s a YouTube video I found when I was repairing the attenuator in my 8902a. ?I followed his procedure and used the same watch repair o ring kit from Amazon (under $10 shipped).

 

Hi Don I searched as you described but didn't find your repair procedure. What is the message number please? Thanks Jason NJ7K?
 

Thanks
Just ordered 50 ? orings.? I have 2 Attenuators to repair.
 

How many of what size/type would be needed to replace all the ones used in an 8566B stack? I'd be interested in buying a set to refurbish my spec an when it becomes necessary.

DaveD
KC0WJN


On Wed, Mar 26, 2025 at 15:29 John Griessen via <john=[email protected]> wrote:
On 3/26/25 10:18, Don Bitters via wrote:
> you will find a detailed step by step procedure with HPAK part nos. and Apple Rubber part nos. for the o-rings.

Is anyone going to be buying 0-rings now?? I'd like to do a group order since I now have an old, mostly working 8566B SA.
These can be mailed around in letters for $.73...
 

On 3/26/25 10:18, Don Bitters via groups.io wrote:
you will find a detailed step by step procedure with HPAK part nos. and Apple Rubber part nos. for the o-rings.
Is anyone going to be buying 0-rings now? I'd like to do a group order since I now have an old, mostly working 8566B SA.
These can be mailed around in letters for $.73...
 

I used 0.5mm CS X 1.0mm ID 70 durometer from theoringstore.com on an attenuator from my HP 8560A
?
?
They are 0.22ea. with a $5.00 minumum order and shipping runs $9.95 so you will have to order 22 to meet their order requirement.
?
I'd order extra and store them in an airtight bag. They are really tiny!
?
Sam
W3OHM
?
?
?
?
 

I have done over a hundred repairs of the 3332xA/B style attenuators. In the file listing in this site you will find a detailed step by step procedure with HPAK part nos. and Apple Rubber part nos. for the o-rings.
You may search the files by my name, or HP 8566 attenuator repair, HP attenuator repair, any of which should find the file.
The short of it is with the attenuator lid off and the contacts in the up (closed) position push the push rod toward the ball opening in the contact slot and lift the contact off from the push rod, when you have them all disconnected pull the solenoid down to the open position. Then you can push the push rods out of the solenoid slots replace the rubber o-rings and put them back into place, reversing the above procedure.

Don Bitters
 

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The original o-rings were 1.0mm ID,2.2mm OD for a cross section of 0.6mm.

None of the ones listed are exactly the correct size.?
 

There's good older threads that go into some detail on this. I repaired one set a few years ago, posting here, and I recall the "surgery" aspect of the project. Mechanically, maybe one of the more demanding projects in this type of work. I used watch o-rings, but there are more appropriate materials and sources of o-rings for this specific purpose.?

I was also able to find a very good video of the procedure on youtube, and I think there are several others available.?

Good luck with the project.?

Radu.?


On Tue, Mar 25, 2025, 11:40 AM ROBERT LEVY via <boblevy4321=[email protected]> wrote:
HiI just disassembled my hp8648 attenuator 33322-60011.
I found the little rubber orings have broke.
I need to know exactly how to disconnect the rods that the orings are on from the contact, without breaking anything.
Thank you to ? Microwaveengineer1968??? for an excellent write up.
?
I found this link to the orings ? ?
?
Thank you
Bob
 

Which size should I select on that page?
I have stuck attenuator sections in three different instruments, seems to be a common problem.
?
Marko Cebokli
 

HiI just disassembled my hp8648 attenuator 33322-60011.
I found the little rubber orings have broke.
I need to know exactly how to disconnect the rods that the orings are on from the contact, without breaking anything.
Thank you to ? Microwaveengineer1968??? for an excellent write up.
?
I found this link to the orings ? ?
?
Thank you
Bob
 

On 12/29/2012 12:51 AM, ffierling wrote:

The drive voltage is nominal under load.

Are you suggesting I compare the coil resistance to a known good
device? By what mechanism would the coil resistance increase - metal
fatigue?

Fred
bad connection(s) to the solenoid winding?

--doug
 

The drive voltage is nominal under load.

Are you suggesting I compare the coil resistance to a known good device? By what mechanism would the coil resistance increase - metal fatigue?

Fred

--- In hp_agilent_equipment@..., Bob Albert <bob91343@...> wrote:

Measure the coil resistance and drive voltage.? It may be that the drive is weak and it's not getting enough coil current, either due to coil resistance increase or drive signal decrease.

Bob

--- On Fri, 12/28/12, ffierling <fff@...> wrote:

From: ffierling <fff@...>
Subject: [hp_agilent_equipment] Re: DIY: Repair of HP Step Attenuators
To: hp_agilent_equipment@...
Date: Friday, December 28, 2012, 2:56 PM

All,

I wonder: I have a sticky microwave relay in an HP 8593A. If the relay has been closed (ie for LOWBAND) for about five minutes and is opened, it won't close again unless it's had a chance to cool down (about 10 minutes at room temp). I can get it to close immediately with freeze-spray. Could this possibly be magnetization? Aside from a sticky relay pivot, how else can such relays fail?

Fred

--- In hp_agilent_equipment@..., "i5spo" <piero.soldi@> wrote:
maybe you have one cell stuck, due to magnetization of the small actuator... Can be locked to the ceiling of attenuator case.


------------------------------------

Yahoo! Groups Links
Bob Albert
 

Measure the coil resistance and drive voltage.? It may be that the drive is weak and it's not getting enough coil current, either due to coil resistance increase or drive signal decrease.

Bob

--- On Fri, 12/28/12, ffierling <fff@...> wrote:

From: ffierling <fff@...>
Subject: [hp_agilent_equipment] Re: DIY: Repair of HP Step Attenuators
To: hp_agilent_equipment@...
Date: Friday, December 28, 2012, 2:56 PM

All,

I wonder: I have a sticky microwave relay in an HP 8593A. If the relay has been closed (ie for LOWBAND) for about five minutes and is opened, it won't close again unless it's had a chance to cool down (about 10 minutes at room temp). I can get it to close immediately with freeze-spray. Could this possibly be magnetization? Aside from a sticky relay pivot, how else can such relays fail?

Fred

--- In hp_agilent_equipment@..., "i5spo" <piero.soldi@...> wrote:
maybe you have one cell stuck, due to magnetization of the small actuator... Can be locked to the ceiling of attenuator case.


------------------------------------

Yahoo! Groups Links





[Non-text portions of this message have been removed]
 

All,

I wonder: I have a sticky microwave relay in an HP 8593A. If the relay has been closed (ie for LOWBAND) for about five minutes and is opened, it won't close again unless it's had a chance to cool down (about 10 minutes at room temp). I can get it to close immediately with freeze-spray. Could this possibly be magnetization? Aside from a sticky relay pivot, how else can such relays fail?

Fred

--- In hp_agilent_equipment@..., "i5spo" <piero.soldi@...> wrote:
maybe you have one cell stuck, due to magnetization of the small actuator... Can be locked to the ceiling of attenuator case.
Steve Reeves
 

I've used a piece of clear tape on the inside edges of the c-frame - works great.

Steve

Sent from my iPod

On Dec 28, 2012, at 2:00 PM, "i5spo" <piero.soldi@...> wrote:



Hi Jarmo,

maybe you have one cell stuck, due to magnetization of the small actuator... Can be locked to the ceiling of attenuator case.
This appened to a good friend of mine, Art iw7jwy.

So the 20 dB cell is always on. Try to do a calibration of S.A.
If it fails, open and check the small 20 dB relay actuator.
A simple repair is to glue a mall tab of mylar inside, on the roof of attenuator, over the sluggish relay actuator.

HTH, Piero.

--- In hp_agilent_equipment@..., "Jarmo" <jarmoblo@...> wrote:

Thanks a lot of this.

I just managed to get a 8568B that attenuator has some problems with the 20dB step.

These instructions encourage me to open the attenuator and clean the pads with isopropyl alcohol. Now it works fine.

I didn't made a testped for it i just cold moved carefully the solenoids and checked with dg8saq vnwa the attenuator pads. I'm not sure is the solenoid stuck or is it actually a contact failure.

The instructions how to disaasemble the attenuator was very accurate and easy to follow.

BR, Jarmo

[Non-text portions of this message have been removed]
i5spo
 

Hi Jarmo,

maybe you have one cell stuck, due to magnetization of the small actuator... Can be locked to the ceiling of attenuator case.
This appened to a good friend of mine, Art iw7jwy.

So the 20 dB cell is always on. Try to do a calibration of S.A.
If it fails, open and check the small 20 dB relay actuator.
A simple repair is to glue a mall tab of mylar inside, on the roof of attenuator, over the sluggish relay actuator.

HTH, Piero.

--- In hp_agilent_equipment@..., "Jarmo" <jarmoblo@...> wrote:

Thanks a lot of this.

I just managed to get a 8568B that attenuator has some problems with the 20dB step.

These instructions encourage me to open the attenuator and clean the pads with isopropyl alcohol. Now it works fine.

I didn't made a testped for it i just cold moved carefully the solenoids and checked with dg8saq vnwa the attenuator pads. I'm not sure is the solenoid stuck or is it actually a contact failure.

The instructions how to disaasemble the attenuator was very accurate and easy to follow.

BR, Jarmo
 

Thanks a lot of this.

I just managed to get a 8568B that attenuator has some problems with the 20dB step.

These instructions encourage me to open the attenuator and clean the pads with isopropyl alcohol. Now it works fine.

I didn't made a testped for it i just cold moved carefully the solenoids and checked with dg8saq vnwa the attenuator pads. I'm not sure is the solenoid stuck or is it actually a contact failure.

The instructions how to disaasemble the attenuator was very accurate and easy to follow.

BR, Jarmo
 

Thanks John!

Best
George

--- In hp_agilent_equipment@..., J Forster <jfor@...> wrote:

FWIW, do it over a tray w/ turned up edges. I just spent over an
hour chasing
small bits of an assembly because I ignored that precaution.

Best,
-John



g47g wrote:

Thanks. I'll try to disassemble the unit, then I hope I'll see the
reason of the failure. [snip]
J Forster
 

FWIW, do it over a tray w/ turned up edges. I just spent over an hour chasing
small bits of an assembly because I ignored that precaution.

Best,
-John



g47g wrote:

Thanks. I'll try to disassemble the unit, then I hope I'll see the
reason of the failure. [snip]

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