HP8595E spectrum Analyzer: readings at -40dB and CAL SIGNAL NOT FOUND

[auato]

Hi,
After a long disuse period I turn it on and after a while it turns off definetively. Once the PSU has been fixed, it runs again but measures almost 40dB less. If I try to calibrate it or try the CONF TEST, it returns "CAL signal not found".

-checked the voltages (all LEDs on PSU are on) and I have TP403=+5.14V,  TP404=+12.10V,  TP401=+14.94V,  TP402=-15.00V but I am not able to find where I can check +24Vdc (it looks that 8590A service manual doesn't mention any 24Vdc rail);
-checked the output calibration signal with another SA and it is OK (300MHz @-20dBm);
-the backup battery still seems to be good (3.01V);
-at the top left, the year has two question marks (attached video);
-in the attached photo I don't remember whether the connector with a purple thin wire starting from the PSU is connected somewhere ;
-if CAL AMPTD runs after entering the deep debug mode (Frequency --> -37Hz) the calibration starts but when it is into the EMI-test part it goes into a loop and no longer exits until I abort the procedure.

But what happened to it?

https://youtu.be/CKte98jvFmI?si=KDvNotXRYJM_psud

edited: I would like to measure +24Vdc

[MarkL]

I would try to characterize the problem a little more.

The first thing I would try is different attenuator settings.  You might have a bad step in your attenuator.

Do you have a signal generator to test the high band (2.9GHz - 6.5GHz)?  Could be a problem with just the low band.

You could try defaulting the calibration constants using the procedure in the Assembly Service Guide.  See "If the analyzer displays a low signal level" on page 234.

On the date/time issue, can you set the date to a sane value, and after unplugging the analyzer for a minute then plugging it back in, does it it keep time?  How long was your "long disuse period"?

I'm not sure if the goofy year could point to possible NVRAM corruption, but it's something to keep in mind.

I'm not seeing a +24V supply on the schematic.  Is there one?

According to the Assembly Service Guide, the purple wire supplies -24V to the A7 analog control board on 8592L and 8593E analyzers.  (I believe it's used to extend the YIG tuning range for those models.)  On the 8595E, it doesn't go anywhere and just terminates in a 3-pin housing that's left hanging.

[DavidAlfa]

You definitely should have 24V, or the switches won't work, just check how the attenuator clearly says 24V, if missing it would explain it all.

Once you have the 24V tested working, if the signal keeps failing:
The attenuator block has four elements (-5, -10, -20, -40dB) and makes a combination of them in series and/or bypassed.
If one of them is burned, you'll get an open circuit.
So try finding a signal by manually setting attenuation to -5, -10, -20 and -40dB.
It's pretty easy to disassemble, but there're a lot of screws behind the cover, where the sma connectors are.
This is it:


One 8592 had that one burned, other had a burned transistor array which activated a rf switch, whose coil was completely roasted, can't remember what it was for.
It was a latching switch, so it only needed a small pulse to change, but the switch contact had fallen (Plastic rivets...), so my guessing is the system did not detect it switching and kept energyzing the coil until it overheated, then everything burned down in a chain.

[MarkL]

You definitely should have 24V, or the switches won't work, just check how the attenuator clearly says 24V, if missing it would explain it all.
...

The label doesn't mean there's a 24V supply.  The attenuator is supplied with +/-15V on J5 pins 3 and 10.  See schematic snippet below.

But the point remains it could still be a bad attenuator step.  I think we both agree on that.

[DavidAlfa]

The label means the coils in the attenuator are meant for 24V, thus the logic tells it'll be powered at that voltage.
These are also available in 5 and 15V versions IIRC.

Or maybe someone replaced the attenuator block with a wrong one?
There're also 5 and 15V versions, so it's strange HP mounted a 24V part there.
Wether HP used them like this, I don't know.

[rf-loop]

HP8594E, 8595E... etc  Attenuator is 24V version ( 33321-60036 ) It have dc bloc, 10, 20 and 40dB attenuator chips

A long time ago I repaired many of these spectrum analyzer attenuators. When it's done well, renovated equals new. But then it is not even opened on a dusty table. Namely, you can't get dust out of there if it gets there or least it is difficult. The dust-sensitive area is the coaxial attenuator tunnel. The outside where the relays are is a normal dirty area.
 Nylon pins and contact strips are very easily damaged, especially the end that is in the attenuator tunnel moving contacts. (the glue on the contact strips may also break and repositioning is the work of a "watchmaker" if you intend to get it in such condition that it has the same specs as new) Most common problems have been burned  attenuator chip (some burned atten chip also visible in @DavidAlfa image) ( and/or) O-rings crumbled broken. The size and material must be correct. I myself have used some Seiko O-rings (spare parts for watches) which in the end cost... yes, quality costs.. The attenuator have 16 0-rings.
For change O-rings work is best to do in right order what is most safe.
In all cases keep all kind of oil far away from these low pressure contact surfaces. They must be absolutely dry and clean. Material is such that it does not require lubrication, even though the surfaces slide just a little bit when contact is made. Instead, there must be a microscopic amount of lubrication at the end of the nylon pin, which must not spread to the contact surfaces under any circumstances, not even when the attenuator changes at a high rate without pause 24/7/365 in some automatic production test line.

[Bicurico]

That was a nice reading, rf-loop. Thank you.

Makes me better understand why these devices were so incredibly expensive.

[auato]

First of all, thank you all for the replies received so far.
I haven't disassembled anything yet. I just did a few more tests that I want to share with you before disassembling the parts.
I performed some measurements having a good signal generator (R&S SMJ100) and another Rigol spectrum analyzer (but with a maximum band of 1.5GHz). What I have noticed is that from 300MHz up to 2GHz, with a signal of 0dBm, generated br SMJ100, I always have a reading of approximately -38dBm (at the default attenuation of 10dB but also at -20 and -30dB but if I move the attenuation from - 40dB up to -70 it becomes a value approximately +2dBm or in any case slightly positive). From 3 to 6GHz I have a reading around -44 / -45dBm which is stable in the various attenuation steps -10, -20 and -30 and which becomes -3 or around -5dBm in the attenuation steps starting from -40dB onwards. The summay is in the picture.

[MarkL]

The label means the coils in the attenuator are meant for 24V, thus the logic tells it'll be powered at that voltage.

Yes, that's not a bad assumption, but it's not the case here.  The attenuator is powered with 30VDC from J5-3 and J5-10 (+/-15V).  There's no ground or other power connections on J5.  The switching is done by pulling the desired input pin to -15V (look at the driver).

The attenuators on both of my 8595E are labeled with "24V".  I've measured the voltages shown on the schematic and they are correct (30VDC supplied as +/-15V).

My point is that there is no +24V supply in the 859xE units for the OP to worry about checking, which was one of the initial questions.

[MarkL]

First of all, thank you all for the replies received so far.
I haven't disassembled anything yet. I just did a few more tests that I want to share with you before disassembling the parts.
I performed some measurements having a good signal generator (R&S SMJ100) and another Rigol spectrum analyzer (but with a maximum band of 1.5GHz). What I have noticed is that from 300MHz up to 2GHz, with a signal of 0dBm, generated br SMJ100, I always have a reading of approximately -38dBm (at the default attenuation of 10dB but also at -20 and -30dB but if I move the attenuation from - 40dB up to -70 it becomes a value approximately +2dBm or in any case slightly positive). From 3 to 6GHz I have a reading around -44 / -45dBm which is stable in the various attenuation steps -10, -20 and -30 and which becomes -3 or around -5dBm in the attenuation steps starting from -40dB onwards. The summay is in the picture.

Hmmm... that's very interesting.  A problem with the 40dB thru path?

Try turning off correction (under CAL --> CORRECT ON/OFF).

[MarkL]

One other thing that might be worthwhile is to look at your calibration constants (CAL --> Service Diag --> DISPLAY CAL DATA) to see if anything is way off.  Typical values are described on page 584, and/or share here.  The cal data and correction constants are stored in NVRAM, and the only reason I bring this up is the unexplained weird (corrupted?) date.

If CORRECT OFF gives you pretty much the same results as before, meaning approx 40dB down when the 40dB attenuator step is supposed to be out, I would say it's time to isolate the attenuator and take a closer look at what it's doing.  The other dB differences you're seeing are relatively much smaller in magnitude, and I wouldn't worry about them yet.  Successful self-calibration might take care of them.

Since you have a signal source and another SA, I would connect the source to the 8595E input (say 300MHz @ 0dBm), and the other SA to watch the signal coming out of the 8595E attenuator.  The attenuator output is the SMA connector on the top (on the end with the ribbon cable).

You can then exercise the attenuator like you did before and watch the changes in output amplitude.

If you get bad behavior with the 40dB step, I wouldn't jump to disassemble the attenuator just yet.  I would confirm that the 40dB step control input is working.  There is a section in the Assembly Repair Guide on what to expect from the control signals on page 291 and table 6-11.

[MarkL]

And also, if you haven't done it already, backup your correction constants using the procedure described in Chapter 3 in the Assembly Repair Guide.  If something goes wrong and you lose the NVRAM, or your battery dies unexpectedly, you'll be much happier.

[auato]

I'm having trouble extracting the assembly to which the attenuator is attached. In meantime I share with you that CAL --> CORRECT OFF does not produce any change and and calibration constants appear as below. I'll update you when I get the attenuator out the assembly... now I have a coaxial that is pulled like a string and I don't understand where it is hooked up and what else I have to dismantle

[DavidAlfa]

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.
Adjust the attenuation level with the knob, from 0dB all the way to -75 or the max. it allows, if it measures open circuit at some point it's very likely you have a bad element.

That's how I got the definitive hint before opening it, the module either bypasses (shorts) or leaves the elements in series, there's no way to create an open circuit except by broken elements.

[rf-loop]

I'm having trouble extracting the assembly to which the attenuator is attached. In meantime I share with you that CAL --> CORRECT OFF does not produce any change and and calibration constants appear as below. I'll update you when I get the attenuator out the assembly... now I have a coaxial that is pulled like a string and I don't understand where it is hooked up and what else I have to dismantle

Are you serious you do not have service manual. There is all explained including disassembly and assembly procedures.

For take attenuator out... you need take rf frontend out first and after then all is more easy. It is very easy when do it just right way. And note that some filters and some other components are mechanically fragile even when they do not looks like fragile and then also care ESD and repeating again: ESD!  Also I recommend keep your tools and fingers out from YTO YIG tuned oscillator except is absolutely necessary.

And then... never enter any DC after attenuator...
(or DC to RF input when DC bloc is turned off...)

You can find a lot of instructions here as well, if you look carefully at what is there to apply.
https://xdevs.com/doc/HP_Agilent_Keysight/08590-90316.pdf

Also due to its age it is wise to check and replace battery. (and even when service manual do not ask to use support battery.. I have always done it with support battery (but it need also take care how to use it)  for keep Mr Murphy outside from my work bench)

There is also somewhere available full CLIP for these (I have only original paper versions, whole repair service set, long time ago purchased from HP/Agilent)

[MarkL]

So sorry you went through the trouble of trying to remove the RF section, and if I said something that implied to do it.  As you are discovering, it's an involved procedure.  I was trying to leave that as a last resort and eliminate all other possibilities first.

More explicitly, and perhaps you can still do this, disconnect the hard coax going to the top of the attenuator (that's the attenuator out) and run an SMA jumper from the attenuator to your Rigol SA.  The attenuator and whole RF section can stay in place.  Then apply your signal generator to the 8595E input and exercise the attenuator as previously described.  See photo.

As for taking the RF section out, it's likely your attenuator is bad and you will have to do this anyway, but my advice would be to take a lot of photos during the disassembly so you will have a record of the cable routing.  (Be thankful you don't have the tracking generator in there too; it's like sausage getting it back together.)

In addition to the instructions in the Assembly Repair Guide (link above from rf-loop), I've also found that removing the screws holding the front panel in place (qty 5 on the sides) and pulling the front panel forward an inch or two will give you a little more working room.  Be sure to disconnect the hard line coax going to the front panel N connector before moving the front panel.

[MarkL]

I would also reinforce rf-loop's concern about DC on the input, and NOT use a DMM to check the resistance.

In order to do a DC resistance check, you need to disable the DC block in the attenuator which is on by default in the 8595E (under AMPLITUDE --> COUPLE DC).  But by doing so you would expose the RF input stages to a DC voltage from the DMM, and possibly damage components there.  Don't do it.

If you really wanted to do a resistance check, disconnect the attenuator output from the RF section (as in the above photo), and put a 50 ohm terminator on the attenuator output.  But because you have a signal generator and another SA, a signal test as previously described is a better confidence test.

EDIT: Doing a resistance check from the front connector is not what DavidAlfa was describing, but since we already had one misunderstanding I want to make sure the point about DC is clear.

[DavidAlfa]

I said doing so between the input and output of the attenuator, which means both sma connectors removed, completely isolated from the analyzer RF input, so no risk of any kind.

[MarkL]

Thanks for posting the CAL DATA DISPLAY.  I'm not an expert on every number in here, but nothing jumps out at me that says the calibration data is invalid.  The AMPLITUDE table looks ok.

The last frequency and amplitude cal is showing as August 11, 2013.  Is that about right?  Has this unit been unused for 10 years?

[MarkL]

I said doing so between the input and output of the attenuator, which means both sma connectors removed, completely isolated from the analyzer RF input.

Yes, I did not mean to say your check was erroneous.  I already edited my post after realizing it could have been interpreted that way.

[DavidAlfa]

Modern DMMs will source pretty low currents, last one I measured did 2mA, was a supercheap meter.
That would put 100mV, 200uW (-7dBm) on the 50Ohm RF input.
I guess good DMMs will provide way lower current.
Would that small DC signal be able to cause any real damage?

[rf-loop]

I said doing so between the input and output of the attenuator, which means both sma connectors removed, completely isolated from the analyzer RF input, so no risk of any kind.

Yes, of course this is a safe way.

However, I wanted to point this out because I have too often seen when something is done slightly different from the instructions, even if just out of curiosity. If by chance such danger factors were not known.

 

[MarkL]

...
There is also somewhere available full CLIP for these (I have only original paper versions, whole repair service set, long time ago purchased from HP/Agilent)

For reference, there is this one that's been copied far and wide, still available from Keysight's server:

  https://www.keysight.com/us/en/assets/9018-05708/user-manuals/9018-05708.pdf

CLIP part number 5963-2951.

It's titled "8590A Component Level Information Packet" (CLIP) on the opening page, but it's actually a CLIP for 859xE/L/C units.  There are nuances for specific E/L/C models and serial number ranges that will appear in other CLIPs, but everything is so similar it doesn't usually matter.

If you ever need to find the exact right CLIP, there is a table on page 521 (Table 12-2) in the Assembly Repair Guide that lists the CLIP part number for specific models and serial number ranges.

[auato]

Hello guys, thank you for the valuable advice you've been giving me. I would like to update you on the test you recommended (especially from @MarkL), which involves directly connecting the attenuator output to a second analyzer and injecting a well known amplitude signal from an external generator. I injected 300MHz at +15dB and here are the results below and in the video:

Att 10dB

-43dBm

Att 20dB

-52dBm

Att 30dB

-60dBm

Att 40dB

-33dBm

Att 50dB

-43dBm

Att 60dB

-53dBm

Att 70dB

-60dBm



https://youtu.be/8tmC3t8NghE?si=OeWIvvGoLs2DWhDO

With attenuation at 40dB, I get the highest reading (-33dBm from +15dBm).
It seems clear that there is something wrong with the attenuator. If I want to exclude the rigid connection and the N connector upstream of the attenuator I would just have to proceed to disassemble the attenuator and try to get my hands on it 

[rf-loop]

Hello guys, thank you for the valuable advice you've been giving me. I would like to update you on the test you recommended (especially from @MarkL), which involves directly connecting the attenuator output to a second analyzer and injecting a well known amplitude signal from an external generator. I injected 300MHz at +15dB and here are the results below and in the video:

Att 10dB

-43dBm

Att 20dB

-52dBm

Att 30dB

-60dBm

Att 40dB

-33dBm

Att 50dB

-43dBm

Att 60dB

-53dBm

Att 70dB

-60dBm



https://youtu.be/8tmC3t8NghE?si=OeWIvvGoLs2DWhDO

With attenuation at 40dB, I get the highest reading (-33dBm from +15dBm).
It seems clear that there is something wrong with the attenuator. If I want to exclude the rigid connection and the N connector upstream of the attenuator I would just have to proceed to disassemble the attenuator and try to get my hands on it 

Once the attenuator is removed and it is on your desk.

Carefully remove the second end piece (4 screws)
Don't open anything else yet!

There is a metal mesh between the end piece and the frame. Note its positioning. also be careful that no dirty / dust of any kind gets into the exposed attenuator cavity.

After the end piece is removed, pull out the aluminum protective case. You can then fasten the end piece back in place (even if only with a couple of screws, just a light finger-tightness) It is also good to be in its place if repair work go forward to next step after detect O rings condition. 

Now that the side of the relays is exposed, you can see the nylon pins that control the attenuator contacts. Each one is on the moving plate of the relay and there are black O-rings. Check carefully whether all O-rings are completely intact. At this stage, you can also move each relay by hand and it will stay in the position you press because of the magnet. In this case, you can see better that all the O rings are in order and that the pins move through their full range of motion. Move every relay and check every single O-ring when nylon pin moves when you turn relay in and out.

I have a 50% prediction that the 40dB attenuator bypass position will not work.
Let's hope problem is O-rings... and nothing else.

Do not disassemble or proceed further until this is resolved.
If the O-rings have a typical defect, next you need the right O-rings and information on how to change them so that the risk of further damage is minimal. It requires the skills and precision of a fine mechanic work. Those nylon pins and contact strips inside attenuator cavity and their fastenings in the attenuator cavity are quite easily damaged, as are the attenuator chips. There are also screws that should not be turned if you want the attenuator's properties to remain correct throughout its frequency range (and those things are not compensated by selfcalibration). Before you get there, you have to do a few things in the right order.