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----- Original Message -----
From: Steve Krull
To: hp_agilent_equipment@...
Sent: Monday, December 31, 2012 3:21 PM
Subject: Re: [hp_agilent_equipment] Re: DIY: Repair of HP 8568B Step Attenuators - another question...



Thanks Karl - I've emailed them to see if they will sell in small
quantities.

Steve K.

On 12/31/2012 12:46 PM, Karl wrote:
>
>
> Ran across these guys while designing a gas analyzer. They make
> all kinds of 0-Rings.
>
>
>
> Karl
>
> --- In hp_agilent_equipment@...
> <mailto:hp_agilent_equipment%40yahoogroups.com>, Steve Krull
> <Steve-Krull@...> wrote:
> >
> > I've got an attenuator for an 8672A that suffers from failed
> O-rings. In
> > this case it appears someone used something nasty to try to clean the
> > spring contacts and attenuator pads and whatever was used dripped down
> > the nylon plungers and turned all the O-rings to a mushy black paste.
> > Not a single survivor. Agilent no longer stocks them but provides the
> > dimensions and material type so I just need to research a source.
> >
> > Steve
> >
> >
> > On 12/30/2012 10:16 PM, pianovt wrote:
> > >
> > > Hi Jim,
> > >
> > > Do not unscrew the solenoids on the top, at least not for now. To see
> > > what's happening, you will have to open the lower part where the RF
> > > action is.
> > >
> > > The two SMA connectors have hex-nuts. Remove them. There is thin name
> > > plate that you can now remove. It covers the whole area between the
> > > SMA connectors. It probably has a few glue spots on its other
> side, so
> > > carefully pry it off without bending the it. Now, you will see a
> bunch
> > > of socket cap screws. When you remove them, you will be able to
> > > carefully separate the parts and gain access to the attenuator pads
> > > and plungers. The rubber O-rings are on the tiny nylon plungers that
> > > are attached to the gold plated spring contacts. I think there are
> two
> > > rings on each plunger, one on the RF side and one on the solenoid
> side.
> > >
> > > Vladan
> > >
> > > --- In hp_agilent_equipment@...
> <mailto:hp_agilent_equipment%40yahoogroups.com>
> > > <mailto:hp_agilent_equipment%40yahoogroups.com>, Jim Schatzman
> > > <james.schatzman@> wrote:
> > > >
> > > > Vladan-
> > > >
> > > > I got the cover off without trouble. By testing I note that when
> the
> > > middle (40 dB) switch is triggered, the output turns off completely.
> > > As far as I can determine, the plunger is actuated correctly. Moving
> > > it manually also results in the loss of output. The other two
> switches
> > > (10 and 20 dB) work fine.
> > > >
> > > > I suppose that either the switch contacts are failing or the 40 dB
> > > resistor is open. Apparently both switches and resistors are inside
> > > the two-piece machined steel block. All the RF path seems to be
> > > inside. It would appear that I need to get this apart, but I am not
> > > sure how to. There are quite a few screws attaching the solenoids to
> > > the steel block, but I am not seeing what is holding the steel block
> > > together.
> > > >
> > > > This attenuator has a PC board with several chips on it. I have
> > > noticed before that HP seems to have adopted the philosophy that if 2
> > > chips are good, then 20 must be better. It is a surprisingly
> > > complicated device.
> > > >
> > > > Any advice??
> > > >
> > > > Thanks!
> > > >
> > > > Jim
> > > >
> > > >
> > > >
> > > > At 08:45 PM 12/30/2012, you wrote:
> > > > >
> > > > >
> > > > >Jim,
> > > > >
> > > > >You will have to pull out the front panel. There are a few
> > > flat-head screws along the front frame (top and bottom, maybe even
> > > sides - don't remember any more). Once you remove them, the front
> > > panel pulls out of the front frame, though it still has a couple of
> > > umbilicals attached. From there, you will see how to get the
> > > attenuator out.
> > > > >
> > > > >The most common failure has to do with the tiny rubber O-rings on
> > > the plungers. This is all delicate magnifier work. Do not succumb to
> > > the "magnetized housing" myth of repair. The attenuator depends on
> > > magnets for latching. It's just that when the O-ring fails and either
> > > splits or falls off, the mechanism shifts closer to the magnet and
> the
> > > force of magnetic attraction increases. At that point, the solenoid
> > > (which has nothing wrong with it) no longer can pull the parts away
> > > from the magnet (which also has nothing wrong with it). This is when
> > > some people decide that demagnetizing everything will fix things. If
> > > you have the patience, study the design, it's interesting. The goal
> > > was to use current only when switching a stage is required and then
> > > interrupt all current to the coils as soon as the task is
> accomplished.
> > > > >
> > > > >You open the attenuator by removing one of the end caps and
> sliding
> > > the U-shaped steel cover off. It comes off relatively easily. Don't
> > > try to remove it by prying with screwdrivers.
> > > > >
> > > > >There are two versions of the attenuators. The older ones are all
> > > electro-mechanical, the newer ones have a p.c. board with some ICs on
> > > them.
> > > > >
> > > > >Good luck, they can be fixed, but the work requires some patience
> > > and you may have to order no O-rings from Agilent.
> > > > >
> > > > >Vladan
> > > > >
> > > > >--- In
> > >
> <mailto:hp_agilent_equipment%40yahoogroups.com>hp_agilent_equipment@...
> <mailto:hp_agilent_equipment%40yahoogroups.com>
> > > <mailto:hp_agilent_equipment%40yahoogroups.com>, Jim Schatzman
> > > <james.schatzman@> wrote:
> > > > >>
> > > > >> All-
> > > > >>
> > > > >> O.k., I have an 8568B with a bad attenuator (40dB and below are
> > > dead).
> > > > >>
> > > > >> My big question is - how do you get access to the attenuator to
> > > take it apart and clean/repair? It seems to be really buried under a
> > > maze of stuff...
> > > > >>
> > > > >> Thanks!
> > > > >>
> > > > >> Jim
> > > > >>
> > > > >>
> > > > >>
> > > > >> At 01:44 PM 12/27/2012, you 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
> > > > >> >
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