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HP8595E spectrum Analyzer: readings at -40dB and CAL SIGNAL NOT FOUND
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auato:
very interesting your pictures. Thank you! Fortunately or unfortunately the o-rings problem doesn't seem to be my case. They look intact.


--- Quote from: DavidAlfa on December 12, 2023, 09:34:35 am ---You can easily check the attenuator without fully disassemblying it, only remove the coax connections and measure resistance with the DMM between input and output.

--- End quote ---
and if I check with a DMM between input and output the resistance is always high (with both the relay positions)
MarkL:

--- Quote from: auato on December 20, 2023, 07:12:11 pm ---very interesting your pictures. Thank you! Fortunately or unfortunately the o-rings problem doesn't seem to be my case. They look intact.


--- Quote from: DavidAlfa on December 12, 2023, 09:34:35 am ---You can easily check the attenuator without fully disassemblying it, only remove the coax connections and measure resistance with the DMM between input and output.

--- End quote ---
and if I check with a DMM between input and output the resistance is always high (with both the relay positions)

--- End quote ---
Don't forget the first attenuator stage, on the opposite end of the ribbon, is a DC blocking capacitor.  So, with this in circuit you won't see any DC resistance.

In combination with the faulty 40db thru position, if you flip all the actuators in the same direction at the same time (all in or all out), you won't have any DC resistance from end to end.

It seems fairly certain there is an issue in the cavity: dirty contact, broken contact, broken nylon pin, etc.  But before digging into it, I would reconnect the ribbon cable to the 8595E one more time and again exercise the actuators: 1) You should be able to identify which one is the 40dB step and 2) Verify the 40dB actuator has the *full* range of motion like the others (nothing is sticking or lopsided).

From your photos everything looks ok from the bottom.  Figuring out which one is the 40dB step will at least allow you to focus on the right set of contacts inside the cavity.
auato:
Guys, I don't know what happened but now everything looks OK. There is probably still something mysterious. Now as you can see from the photo, the attenuator is still outside and the HP8595E only controls the relay contacts. The attenuation steps are OK and represented as in the photo. 
frankly I still don't know what to do. I was not so keen on getting my hands inside that attenuator with those tiny mechanisms. Maybe it's dirty inside and I recall that I only sprayed some compressed air on it. In any case I studied what to do watching some videos on YT on how to operate with this stuff and if the problem will appear again, I will proceed with a disassembly of it. I could wait a few more days and then proceed with the assembly. First, however, I would like to replace that 10 ohm resistor R80 in the photo that I clumsily smoked on the analog board A7. Anyway I will keep you updated. In the meantime, Merry Christmas to all of you and thanks again
MarkL:
Well, glad it's working.  But unexplained, it will of course come back at the most inopportune time.

Thanks for documenting the attenuator dB step positions.
rf-loop:
@auato

It is possible there have been some small piece of what ever inside attenuator relay side.
But in more worst case there can be some other problem inside attenuator cave. I do not list all what are somehow possible.

I think your some one previous images was not from your attenuator but similar (because it is partially disassembled and bit weird way, perhaps just for image...who knows). I have used this image (part of it) here.





There need always carefully look these positions are clean (marked red arrows). These metal surfaces need be free from some small garbage and also these surfaces of nylon pins, so that it can move perfectly full amount. (I have seen many times example small piece of old brittle O-ring rubber on these surfaces, sometimes these are like attached there and need carefully remove if they exist and if still do not yet want do whole renew work (there is two methods for take nylon needles out from contact strips in cave - very risky "lottery" way  or very safe but lot of more "watchmaker" work. (example I use always dust free air room and and magnifier (microscope in my case dye to my after "best before" aged eyes )

Btw, in some pictures in this thread can see some attenuators where can see bit weird contact strips and also really weird contact strips positions... without further explanations and other images can not tell what are these and why... there is one image where strips are positions I have never seen when nylon needles have removed... really weird. (but because it is not your attenuator ... no need think more these)

If you use compressed air to inside attenuator cave. Be very careful because these thin contact strips. They are fragile. Some times also old glue can brittle (they are glued in perfect positions). Also air need be real clean and oil free, and still it can do more bad than good because some particles attached to the surfaces inside may detach and then remain in contact. The low contact pressure contact is to some extent "self-cleaning", however, because there is a small slip when the contact is made... gold alloy against gold alloy.

If the cavity of the attenuator and the end flanges have never been opened, it is quite unlikely that there is debris there. The holes of the nylon needles have quite a small clearance, so normally no debris gets in there.
But what have I ever found. Rarely. Some kind of "oil" or "grease". It is put in when the witches are made. There, at the point of contact between the nylon needles and the contact strips. Usually it is a very small dose. And it must never come into contact with the surface. Sometimes the attenuators run very hot (production test use, for example, is very tough, the user's HP didn't even give them a warranty for that use).
In such a situation, the fat may heat up and drain, especially if there has been a bit too much of it there. Grease between the contact surface does not prevent contact. But then the typical problem is that during the SelfCal / Self Check phase the contact is created a little too slowly and it fails or sometimes even gives the wrong value (capasitive contact just before galvanic)

Merry Christmas!
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