|
Since Agilent continiously ups the spare part prices and discontinues
parts it has become more and more important to go past normal repair
practices.
Step Attenuators for example can be repaired without any special
tools or cleanroom enviroment !
Lets take a look at the failure modes first, there are a few:
1.) Blown pads
Usually common with spectrum analyzers if a level past the damage
level of the attenuator was applied
2.) Cracked pads, pad has developed a hairline crack due to
mechanical stress !
3.) Improper contact, the contact in between the attenuator and
contact fingers is disturbed.
4.) Stuck solenoid
Quite common if attenuator hasnt been used in awhile
After we remove the attenuator from the instrument the first step is
to obtain the pinout and build us a little test bench consisting of a
powermeter and a signal generator, the good old 8481D or 8484A will
do nicely, if you dont have a sig gen use the 50MHz calibrator output
of the 435 or 436 or similar model, connect the cal output to the
30dB pad connect the sensor and zero and calibrate meter, the meter
will read -30dBm.
Disconnect the sensor from the attenuator and insert the Step
Attenuator, set step attenuator to 0dB, note the level on the
powermeter, now switch in the attenuator sections one by one measure
and note the level, 70dB attenuators are comprised of a 10 20 and
40dB Pad while 110dB Attenuators normally comprise of a 10 20 and two
40dB pads !
check every section individually, you should hear a click as you
enable each section, if you find a bad section note the value it
should have if all sections appear to be good repeat the test at a
higher frequency using a sig gen, if everything appears to be ok at
low frequency then most likely you have attenuator that just needs
cleaning.
Now lets take the attenuator apart, looking at the top you will see a
nut on each SMA connector, remove this nut this will allow for you to
remove the nameplate, under the plate you will see a wealth of allen
screws, remove those but note that the screws close to the SMA
connector are shorter than the other ones.
Now look at the small sideplate, not the one with the ribbon cable
but the other side - there are 4 small allen screws, remove those and
then remove the sideplate, careful not to lose the little wire mesh
here ! now slide out the u shaped cover and remove the top side.
You now have two parts, one beein the bottom side containing the
solenoids and the other one beein the top part containing the
attenuator pads.
First lets inspect the pads, you can measure them with a ohm meter,
they should measure in the vicinity of 50ohms , except of the 10dB
pad which can measure up to 70ohms or more.
Inspect the pads visually, are there any burned or cracked pads ? if
all pads look ok and check out at DC take a surgical swab and
isopropilic alcohol and carefully clean the contacts pads on the
attenuators.
Next look at the contacts, enable all solenoids and observe the
position of the contact tongues, they should be slightly above the
surface of the block, carefully clean the contact tongues with
alcohol, be careful not to bend them.
next put the solenoids back into the 0 position and look at the top
of the solenoids, you will see two little white plastic rods where
those meet the solenoid you should see little rubber rings , there
are 4 of those on each segment, usually over the years they go
briddle and then disappear, with those rings gone the attenuator wont
make contact anymore, you can buy the rings from watchmakers supply
stores as they are beein used for sprocket gaskets !
Now if your gaskets are there put the attenuator back together after
you cleaned everything and it should work now.
If you have a broken or burned pad dont stress over it the pads are
used in all HP attenuators so just find a attenuator on ebay and take
the pad you need out of it, you can also buy pads from agilent
however be prepared to pay $100-150 per
piece
|
Hi Lothar, I have a 8495A manual step attenuator, and though it has the correct attenuations on every step(?), but it needs force to switch the attenuator in different positions, and also the well known "click" cannot be heard, when turning (with some force) the knob. Could you help me with some idea and procedure, as you did with the electronic controlled equivalent ? Thanks George Galambos --- In hp_agilent_equipment@..., "microwaveengineer1968" <microwaveengineer1968@...> wrote:
Since Agilent continiously ups the spare part prices and discontinues
parts it has become more and more important to go past normal repair
practices.
Step Attenuators for example can be repaired without any special
tools or cleanroom enviroment !
Lets take a look at the failure modes first, there are a few:
1.) Blown pads
Usually common with spectrum analyzers if a level past the damage
level of the attenuator was applied
2.) Cracked pads, pad has developed a hairline crack due to
mechanical stress !
3.) Improper contact, the contact in between the attenuator and
contact fingers is disturbed.
4.) Stuck solenoid
Quite common if attenuator hasnt been used in awhile
After we remove the attenuator from the instrument the first step is
to obtain the pinout and build us a little test bench consisting of a
powermeter and a signal generator, the good old 8481D or 8484A will
do nicely, if you dont have a sig gen use the 50MHz calibrator output
of the 435 or 436 or similar model, connect the cal output to the
30dB pad connect the sensor and zero and calibrate meter, the meter
will read -30dBm.
Disconnect the sensor from the attenuator and insert the Step
Attenuator, set step attenuator to 0dB, note the level on the
powermeter, now switch in the attenuator sections one by one measure
and note the level, 70dB attenuators are comprised of a 10 20 and
40dB Pad while 110dB Attenuators normally comprise of a 10 20 and two
40dB pads !
check every section individually, you should hear a click as you
enable each section, if you find a bad section note the value it
should have if all sections appear to be good repeat the test at a
higher frequency using a sig gen, if everything appears to be ok at
low frequency then most likely you have attenuator that just needs
cleaning.
Now lets take the attenuator apart, looking at the top you will see a
nut on each SMA connector, remove this nut this will allow for you to
remove the nameplate, under the plate you will see a wealth of allen
screws, remove those but note that the screws close to the SMA
connector are shorter than the other ones.
Now look at the small sideplate, not the one with the ribbon cable
but the other side - there are 4 small allen screws, remove those and
then remove the sideplate, careful not to lose the little wire mesh
here ! now slide out the u shaped cover and remove the top side.
You now have two parts, one beein the bottom side containing the
solenoids and the other one beein the top part containing the
attenuator pads.
First lets inspect the pads, you can measure them with a ohm meter,
they should measure in the vicinity of 50ohms , except of the 10dB
pad which can measure up to 70ohms or more.
Inspect the pads visually, are there any burned or cracked pads ? if
all pads look ok and check out at DC take a surgical swab and
isopropilic alcohol and carefully clean the contacts pads on the
attenuators.
Next look at the contacts, enable all solenoids and observe the
position of the contact tongues, they should be slightly above the
surface of the block, carefully clean the contact tongues with
alcohol, be careful not to bend them.
next put the solenoids back into the 0 position and look at the top
of the solenoids, you will see two little white plastic rods where
those meet the solenoid you should see little rubber rings , there
are 4 of those on each segment, usually over the years they go
briddle and then disappear, with those rings gone the attenuator wont
make contact anymore, you can buy the rings from watchmakers supply
stores as they are beein used for sprocket gaskets !
Now if your gaskets are there put the attenuator back together after
you cleaned everything and it should work now.
If you have a broken or burned pad dont stress over it the pads are
used in all HP attenuators so just find a attenuator on ebay and take
the pad you need out of it, you can also buy pads from agilent
however be prepared to pay $100-150 per
piece
|
most likely the cam is worn out or the little ball that locks the cam in place is missing g47g <g47g@...> wrote: Hi Lothar, I have a 8495A manual step attenuator, and though it has the correct attenuations on every step(?), but it needs force to switch the attenuator in different positions, and also the well known "click" cannot be heard, when turning (with some force) the knob. Could you help me with some idea and procedure, as you did with the electronic controlled equivalent ? Thanks George Galambos --- In hp_agilent_equipment@..., "microwaveengineer1968" <microwaveengineer1968@...> wrote:
Since Agilent continiously ups the spare part prices and discontinues
parts it has become more and more important to go past normal repair
practices.
Step Attenuators for example can be repaired without any special
tools or cleanroom enviroment !
Lets take a look at the failure modes first, there are a few:
1.) Blown pads
Usually common with spectrum analyzers if a level past the damage
level of the attenuator was applied
2.) Cracked pads, pad has developed a hairline crack due to
mechanical stress !
3.) Improper contact, the contact in between the attenuator and
contact fingers is disturbed.
4.) Stuck solenoid
Quite common if attenuator hasnt been used in awhile
After we remove the attenuator from the instrument the first step is
to obtain the pinout and build us a little test bench consisting of a
powermeter and a signal generator, the good old 8481D or 8484A will
do nicely, if you dont have a sig gen use the 50MHz calibrator output
of the 435 or 436 or similar model, connect the cal output to the
30dB pad connect the sensor and zero and calibrate meter, the meter
will read -30dBm.
Disconnect the sensor from the attenuator and insert the Step
Attenuator, set step attenuator to 0dB, note the level on the
powermeter, now switch in the attenuator sections one by one measure
and note the level, 70dB attenuators are comprised of a 10 20 and
40dB Pad while 110dB Attenuators normally comprise of a 10 20 and two
40dB pads !
check every section individually, you should hear a click as you
enable each section, if you find a bad section note the value it
should have if all sections appear to be good repeat the test at a
higher frequency using a sig gen, if everything appears to be ok at
low frequency then most likely you have attenuator that just needs
cleaning.
Now lets take the attenuator apart, looking at the top you will see a
nut on each SMA connector, remove this nut this will allow for you to
remove the nameplate, under the plate you will see a wealth of allen
screws, remove those but note that the screws close to the SMA
connector are shorter than the other ones.
Now look at the small sideplate, not the one with the ribbon cable
but the other side - there are 4 small allen screws, remove those and
then remove the sideplate, careful not to lose the little wire mesh
here ! now slide out the u shaped cover and remove the top side.
You now have two parts, one beein the bottom side containing the
solenoids and the other one beein the top part containing the
attenuator pads.
First lets inspect the pads, you can measure them with a ohm meter,
they should measure in the vicinity of 50ohms , except of the 10dB
pad which can measure up to 70ohms or more.
Inspect the pads visually, are there any burned or cracked pads ? if
all pads look ok and check out at DC take a surgical swab and
isopropilic alcohol and carefully clean the contacts pads on the
attenuators.
Next look at the contacts, enable all solenoids and observe the
position of the contact tongues, they should be slightly above the
surface of the block, carefully clean the contact tongues with
alcohol, be careful not to bend them.
next put the solenoids back into the 0 position and look at the top
of the solenoids, you will see two little white plastic rods where
those meet the solenoid you should see little rubber rings , there
are 4 of those on each segment, usually over the years they go
briddle and then disappear, with those rings gone the attenuator wont
make contact anymore, you can buy the rings from watchmakers supply
stores as they are beein used for sprocket gaskets !
Now if your gaskets are there put the attenuator back together after
you cleaned everything and it should work now.
If you have a broken or burned pad dont stress over it the pads are
used in all HP attenuators so just find a attenuator on ebay and take
the pad you need out of it, you can also buy pads from agilent
however be prepared to pay $100-150 per
piece
--------------------------------- Get easy, one-click access to your favorites. Make Yahoo! your homepage.
|
Thanks. I'll try to disassemble the unit, then I hope I'll see the reason of the failure. --- In hp_agilent_equipment@..., lothar baier <microwaveengineer1968@...> wrote:
most likely the cam is worn out or the little ball that locks the
cam in place is missing
g47g <g47g@...> wrote: Hi Lothar,
I have a 8495A manual step attenuator, and though it has the correct
attenuations on every step(?), but it needs force to switch the
attenuator in different positions, and also the well known "click"
cannot be heard, when turning (with some force) the knob.
Could you help me with some idea and procedure, as you did with the
electronic controlled equivalent ?
Thanks
George Galambos
--- In hp_agilent_equipment@..., "microwaveengineer1968"
<microwaveengineer1968@> wrote:
Since Agilent continiously ups the spare part prices and discontinues
parts it has become more and more important to go past normal repair
practices.
Step Attenuators for example can be repaired without any special
tools or cleanroom enviroment !
Lets take a look at the failure modes first, there are a few:
1.) Blown pads
Usually common with spectrum analyzers if a level past the damage
level of the attenuator was applied
2.) Cracked pads, pad has developed a hairline crack due to
mechanical stress !
3.) Improper contact, the contact in between the attenuator and
contact fingers is disturbed.
4.) Stuck solenoid
Quite common if attenuator hasnt been used in awhile
After we remove the attenuator from the instrument the first step is
to obtain the pinout and build us a little test bench consisting of a
powermeter and a signal generator, the good old 8481D or 8484A will
do nicely, if you dont have a sig gen use the 50MHz calibrator output
of the 435 or 436 or similar model, connect the cal output to the
30dB pad connect the sensor and zero and calibrate meter, the meter
will read -30dBm.
Disconnect the sensor from the attenuator and insert the Step
Attenuator, set step attenuator to 0dB, note the level on the
powermeter, now switch in the attenuator sections one by one measure
and note the level, 70dB attenuators are comprised of a 10 20 and
40dB Pad while 110dB Attenuators normally comprise of a 10 20 and two
40dB pads !
check every section individually, you should hear a click as you
enable each section, if you find a bad section note the value it
should have if all sections appear to be good repeat the test at a
higher frequency using a sig gen, if everything appears to be ok at
low frequency then most likely you have attenuator that just needs
cleaning.
Now lets take the attenuator apart, looking at the top you will see a
nut on each SMA connector, remove this nut this will allow for you to
remove the nameplate, under the plate you will see a wealth of allen
screws, remove those but note that the screws close to the SMA
connector are shorter than the other ones.
Now look at the small sideplate, not the one with the ribbon cable
but the other side - there are 4 small allen screws, remove those and
then remove the sideplate, careful not to lose the little wire mesh
here ! now slide out the u shaped cover and remove the top side.
You now have two parts, one beein the bottom side containing the
solenoids and the other one beein the top part containing the
attenuator pads.
First lets inspect the pads, you can measure them with a ohm meter,
they should measure in the vicinity of 50ohms , except of the 10dB
pad which can measure up to 70ohms or more.
Inspect the pads visually, are there any burned or cracked pads ? if
all pads look ok and check out at DC take a surgical swab and
isopropilic alcohol and carefully clean the contacts pads on the
attenuators.
Next look at the contacts, enable all solenoids and observe the
position of the contact tongues, they should be slightly above the
surface of the block, carefully clean the contact tongues with
alcohol, be careful not to bend them.
next put the solenoids back into the 0 position and look at the top
of the solenoids, you will see two little white plastic rods where
those meet the solenoid you should see little rubber rings , there
are 4 of those on each segment, usually over the years they go
briddle and then disappear, with those rings gone the attenuator wont
make contact anymore, you can buy the rings from watchmakers supply
stores as they are beein used for sprocket gaskets !
Now if your gaskets are there put the attenuator back together after
you cleaned everything and it should work now.
If you have a broken or burned pad dont stress over it the pads are
used in all HP attenuators so just find a attenuator on ebay and take
the pad you need out of it, you can also buy pads from agilent
however be prepared to pay $100-150 per
piece
---------------------------------
Get easy, one-click access to your favorites. Make Yahoo! your
homepage.
|
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:
toggle quoted message
Show quoted text
Thanks. I'll try to disassemble the unit, then I hope I'll see the
reason of the failure. [snip]
|
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]
|
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
|
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.
toggle quoted message
Show quoted text
--- 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
|
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]
|
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
toggle quoted message
Show quoted text
--- 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.
|
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
toggle quoted message
Show quoted text
--- 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]
|
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
toggle quoted message
Show quoted text
--- 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
|
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
|
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
|
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
|
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.?
|
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.
|
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
?
?
?
?
|
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...
|
Sam Reaves