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Vladan and the group -

Wow! That is one fancy piece of miniature mechanical manufacturing. Like a Swiss watch. Beautiful. Crazy. Amazing.

Unfortunately, the 40 dB attenuator is indeed open at one end. And it is nothing like a few simple resistors. It is a beautiful glass contraption about 5 mm by 10 mm with gold and resistive elements plated in a fancy pattern.

Any ideas how I can get a new one?

It is open on the input end. It would appear that someone set the SA for 40dB attenuation and then attached it to some high power source. Apparently, the perpetrator failed to read the manual where it explains (multiple times) that the input limit is 30 dBm AT ALL ATTENUATOR SETTINGS!

Actually, I am kind of surprised that this delicate device can even take 30 dBm. Maybe it really can't....

Thanks!

Jim





At 09:16 PM 12/30/2012, you 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 <mailto:hp_agilent_equipment%40yahoogroups.com>hp_agilent_equipment@..., 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@..., 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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