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Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?

 

On Tue, Sep 3, 2024 at 09:02 AM, Tom Lee wrote:
it's hard to see how a few microamps of forward current could cause an increase in reverse leakage current.
yes... agreed... it's 'hard to see' ... it's an obvious typo... and obviously wrong.
since... reverse leakage current (as it is well known... and shown... in data sheets) increases exponentially with temperature... and not small forward current.
Though... if someone in the group can show that "a few uA of forward current [can] cause an increase in reverse leakage current," at least one person is interested.
Such a discovery could cause a revolution in generating topics for scientific research.
Hypotheses for research might be based on the uncharitable interpretations of obvious, and unintentional mistakes, in forum posts and comments... or not.
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Re: Keysight customer support policy

 

Back when they were still Agilent, I bought a loaded E4404b Spectrum analyzer Around $50 US. No problem. A few years later I needed to replace
the Dallas battery/memory chip. I ordered one from their website. Thinking 'no problem' since it took my credit card. Nope, a week later I get an email
saying they won't sell to me unless my email domain matches a company name with the same domain. No gmail. After a couple of back and forths, I
ordered it from Digikey (less money even). Still they send me a few emails each week trying to sell me new equipment. Go figure.
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Russ
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Re: Keysight customer support policy

 

If you are *not* a large corporate client you can pretty much give up on it.? A fairly long discussion was here:
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While keysight no doubt has what, to them, are valid reasons to completely abandon and non corporate customer I personally feel that this is quite short sighted of them especially considering that there are many. many alternatives that have equal if not better performance - with excellent customer service for *all* buyers and all at a fraction of the cost.? Even in the corporate world, the smaller entities seem to be increasingly marginalized over the larger clients.? In the above post I believe that I mentioned someone who was very much ignored by Keysight over multiple occasions when trying to work out an issue with a piece of equipment that they bought for their personal use; unfortunately for Keysight, they also happened to be very influential with the equipment requirements for a rather large project and Keysight was dropped in favor of other vendors.? To the best of my knowledge that has, to date, cost Keysight well into the 8 figures.? For a company as large as Keysight that might not exactly be a case of shooting yourself in the foot but it should at least count as dropping a hammer on your toe.
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While I absolutely love restoring and using my vintage HP equipment, all my new stuff is from Keithley, Tektronix, Siglent and so forth and I couldn't be happier or more satisfied with it's performance.
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Hal
Re: Keysight customer support policy

 

Thanks!
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No, I don't have a web page yet, only an empty domain. I'm afraid I may get work if I set it up ;-)
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The sensor:
Yes, that was my first thought. DIY. Try to find a donor or see if it can be fixed one way or the other.
However, as it's working, I'm reluctant to do "advanced surgery".
What you suggest sounds not too bad, so I will try. I'm not afraid of screw driver marks or residue.
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The question to Keysight was to get an idea what it might cost to fix it the official way. Sometimes it can really be worth it, but I feel not too welcome.
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It sounds very plausible what you describe, and much in line with my own experience with few exceptions.
Re: 8497K attenuator overhaul

 

On Tue, Sep 3, 2024 at 11:54 AM, pianovt wrote:
No o-rings in the manual attenuator.
yes .. my bad - I looked at the wrong picture!
Re: 8497K attenuator overhaul

 

On Tue, Sep 3, 2024 at 11:40 AM, vk2bea wrote:
I was right about the camshaft on the manual attenuator (and it does have o-rings)
No o-rings in the manual attenuator.
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Vladan
Re: 8497K attenuator overhaul

 

That looks a little odd .. with the 'SMA' male threads on the outside.
I figured there must be thread locker if it is an adapter.
Re: 8497K attenuator overhaul

 

I was right about the camshaft on the manual attenuator (and it does have o-rings) ...
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BTW I should have said SMA male to N female adapter.
Re: 8497K attenuator overhaul

 

The attached picture is not of a 8497K, but I think you can see what the connector looks like on the inside end. You will have to remove the N-connector in order to get to the socket head screws under the connector body. The N connector transitions to SMA which then screws into the attenuator housing. The problem is Locktite. The inner part of the N connector is retained in the stainless body with Locktite, and the SMA end is also retained with Locktite in the attenuator body. It will not feel nice while you are unscrewing the connector. Usually, the smaller thread (SMA) will breal loose, but it in theory it could happen that the thread in the connector releases first. I doubt it will.
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In other words, removing the N connector is equivalent to removing the SMA connector on an attenuator that has SMA connectors. The difference is, you don't have to remove the SMA in order to replace the rings on an attenuator with SMAs.
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Vladan

IMG_9696.JPG

Re: 8497K attenuator overhaul

 

I am assuming that the design is the same as the SMA type that I overhauled from the spectrum analyzer. (I think reasonable).
I'm not sure the same would apply with the mechanical version but they may have replaced the solenoids with cams. (just speculating)
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Between the N F/M and the faceplace on my unit I can see what looks like a nut. It's possible that this is built as an SMA attenuator with the addition of SMA F/M to N F/M adapters. I haven't seen such adapters elsewhere but if that is a nut, there would be no other way to disassemble the unit other than to unscrew the N to SMA adapter (to get at the nut).
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Michael
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Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?

 

¿ªÔÆÌåÓý

Hi Tom ¨C

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I admire your restraint and diplomatic prowess. I do not think I would be able to come close to your exemplar demeanor. Knowing not only this group, but many others, there are always answers. Usually too many, with few if any correct. They also go on endlessly. Your students must be pleased and honored to have you. Best Regards ¨C Mike ?

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Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

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-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Tom Lee
Sent: Tuesday, September 3, 2024 12:02 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?

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I suppose almost anything is possible, but it's hard to see how a few microamps of forward current could cause an increase in reverse leakage current. Knowing this group, however, someone will chime in with a possible mechanism, I'm sure!

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Schottkys are particularly sensitive to reverse breakdown -- even for very brief instants, so diode engineers often add a guard-ring around the Schottky to produce a protective PN junction diode in parallel with the Schottky. The junction diode is designed to break down first and protect the Schottky. It may be that early Schottkys did not use this arrangement, so perhaps that's what HP was reacting to. Or not.

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--Tom

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--

Prof. Thomas H. Lee

Allen Ctr., Rm. 205

420 Via Palou Mall

Stanford University

Stanford, CA 94305-4070

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Virus-free.
Re: 8497K attenuator overhaul

 

These things have o-rings to replace? I didn't know!
I just ordered a fistful of silicone o-rings from 'The O-Ring Store' for the attenuators in my 8648C sig gens, plus a bunch extras for future use.
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I also have an 8494B with manual knob, should I look into servicing it too? (It is an N-type like yours).
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Jared
Re: Keysight customer support policy

 

Hello Bo,
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I think you are confronting two non-technical problems, in addition to the technical one regarding the connector.
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My guess is that Keysight is trying to deal with regulations regarding EU right to repair law(s) as they apply to consumers. They do this by limiting themselves to business-to-business (B2B) transactions only.
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The other problem is that Keysight is going the way of most other companies in treating employees and customers as ¡°resources¡±. In other words, while they still make some excellent products, things are not as they used to be. I don¡¯t see them reverting to the old days. The company is now much more of a pressure cooker. The current CEO has a sales background, so you can expect him to ¡°monetize¡± everything he can think of. You may be fighting an uphill battle dealing with the system, so consider tightening the connector by yourself.
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As to the technical problem, it sounds like you may need to open the plastic case and tighten the connector where it meets the main body. I don¡¯t have an E4413A. However the plastic housing looks similar in design to older sensors, which can be pried open for repair without destroying the plastic. It is difficult to do this without leaving some prying marks in the plastic, but it can be done if you pick the perfect srewdriver. Once you remove the plastic shell, there should be two flats on the connector body for a wrench. I don't think there is a need to open the metal housing, but I have never worked on an E4413A. That¡¯s my guess as to what needs to done. Maybe there is a picture somewhere on the web showing the sensor without the plastic housing.
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To see how the plastic housing can be opened, download the manual for a 8481 or 8482 sensor. The older manuals contain the instructions. Do not remove the two labels on the side of the plastic housing, there is no need to do that. If you have some questions, send me an email.
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Alternatively, submit your inquiry to Keysight via a business address.
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Vladan
Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?

 

I suppose almost anything is possible, but it's hard to see how a few microamps of forward current could cause an increase in reverse leakage current. Knowing this group, however, someone will chime in with a possible mechanism, I'm sure!

Schottkys are particularly sensitive to reverse breakdown -- even for very brief instants, so diode engineers often add a guard-ring around the Schottky to produce a protective PN junction diode in parallel with the Schottky. The junction diode is designed to break down first and protect the Schottky. It may be that early Schottkys did not use this arrangement, so perhaps that's what HP was reacting to. Or not.



--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

On 9/2/2024 6:11 PM, Edward Prest wrote:
Is this failure is related to having a few uA running through the metal junction for decades?
Personally, if it took 30+ years to get so leaky, then I would still replace it with a new schottky - and a new battery.
Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?

 

On Mon, Sep 2, 2024 at 06:11 PM, Edward Prest wrote:
if it took 30+ years to get so leaky, then I would still replace it with a new schottky - and a new battery.?
I agree.
I'm not an 'expert' but 'experts' maybe don't know what really goes on at a fab (or what prayers the engineers say, during the fabrication process.)
Maybe materials are 'better' and 'clean rooms' are cleaner too.
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Anyway to hold back against a cell (or battery) discharging into the charging circuit... perhaps a BAT42 (or BAT 43) ... which has about 0.3 V drop, at 10 mA forward voltage, and about 100 nA at 10 volts reverse voltage, at 25 C.? Maybe those would do.
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Reverse leakage current increases exponentially with current. So maybe it's not a good idea to cook these things.
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And yes...how many of these fine instruments... with SRAM battery backup problems... are going to be in use... even 10 years from now... especially, by the person whose problem this originally was.
Re: HP 141T Power Supply Help Needed

 

Hi guys,

Good points here. What happens when you place a cap with zero ESR

at the output of a linear power supply is that you intrude on the phase margin

and the loop becomes unstable. This can easily be verified by running an

LTspice simulation.

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The remedy would be to add a small series resistor to the cap. I have seen this

done in the hp8640B signal generator power supply - a long time ago.

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What is worth noting is that the output cap is part of the load and not part of the loop.

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G?ran
Re: Keysight customer support policy

 

On Tue, 3 Sept 2024 at 11:35, Bo in Finland via <bfredr=[email protected]> wrote:
<clip>

Our support team forwarded your inquiry to the contact center in Finland.

Kindly note that Keysight products are designed, manufactured and tested for professional and industrial use. They are not designed or tested for use by Consumers and therefore we are not able to supply them or provide service for them in case you are a private individual.

In case you work for a company, kindly provide us the company name and address as well as your company email address and we can continue working with your inquiry.

<clip>

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Anyone with ideas about one (the sensor) or the other (bypass the policy-barrier)?

I'm happy to give the details Keysight ask for once I get in contact with a real and friendly person.

Obviously the sensor is more interesting now, but I have one other Agilent component to ask about.


You work as a freelance consultant. It might help to have a web page you can point them to.
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Keysight customer support policy

 

Hi group,
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I tried asking Keysight support for possibility to repair or buy spare parts for a HP E4413A 26.5 GHz power sensor and giving the serial number and my full name.
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The sensor works fine, but the 3.5mm connector is suspect.
Both the center pin and the ground connection can easily be rotated.
Not sure this is a standard feature or potential problem so I asked support.
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However, I seem to end up at a AI-generated door guard asking me to register whatever reply I give.
I don't find it very meaningful to start registering before I even know if I have a problem or not.
At first I think I got in contact with the US support, but after few unfruitful trials they sent me to the Finnish representative repeating the :
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<clip>

Our support team forwarded your inquiry to the contact center in Finland.

Kindly note that Keysight products are designed, manufactured and tested for professional and industrial use. They are not designed or tested for use by Consumers and therefore we are not able to supply them or provide service for them in case you are a private individual.

In case you work for a company, kindly provide us the company name and address as well as your company email address and we can continue working with your inquiry.

<clip>

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Yes, I'm a retired professional with long experience dealing with/buying from HP and Agilent, and with my own quite inactive design company, but how to ask a fair question without filling my "shoe-number" first?

I value privacy and respect.

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Anyone with ideas about one (the sensor) or the other (bypass the policy-barrier)?

I'm happy to give the details Keysight ask for once I get in contact with a real and friendly person.

Obviously the sensor is more interesting now, but I have one other Agilent component to ask about.

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Thanks!

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Re: Crystal detector with 10dB attenuator in series - is it for matching purposes?

 

Excellent answers, thanks all.
Re: HP 141T Power Supply Help Needed

 

To amplify your comment, many times older linear supplies,
when they are brute force recapped, with the best, long life,
low esr caps you can find, will become beacons of chaotic
oscillation.

I put a low ESR ceramic capacitor in the feedback loop of a unity
gain OPAMP circuit the other day, and was amazed that it went
totally unstable. It was an older LM301 variety, where the
response characteristics of the opamp are a blank slate until
the designer adds in the stability network. The designer's
efforts were wiped out by my ceramic capacitor replacement
for his 1uf back-to-back emulation of a non-polar electrolytic.

Sometimes the modern best replacement is not suitable for use
in an older instrument.

-Chuck Harris


On Mon, 2 Sep 2024 22:40:20 +0100 "Dave_G0WBX via groups.io"
<g8kbvdave@...> wrote:
Hi.

It's just a generic term (damping is another) to slow down the
response of a loop, to prevent it going unstable.

Not an uncommon issue in some linear PSU's like those -12.6V or -100V
regulator topologies that are not "conventionally" laid out.

Unless you 'scope the thing, you often don't know it's gone unstable,
other than some passive parts sometimes cook for no obvious reason.?
(That R49 for example!? See Mike's comment in another mail.)

It is also not uncommon, when modern transistors are used to replace
older failed parts (that are not available any more) and the new
device has "a lot" more gain at HF than the originals, that regulator
or other control loops suddenly become "unruly" under some operating
conditions.

Sometimes a low value "Base Stopper" resistor (a few Ohms, or a
ferrite bead) in series with the new device's Base connection can
restore sanity!

Take care.

Dave B.
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