Repair and experiments thread: HP 3458A U2

[saturnin]

I don't think Fluke metrology DMM engineers don't know what it's ADC linearity. I just think it's not told to public directly, as it would not look good versus old proven 3458A. Fluke Primary standards lab have JJA unit, and I'm sure they are more than capable to perform measurements and validation of 0.1ppm-linear ADC. Publication of such data on website though is another question.

FYI. A typical example of type testing linearity on the Fluke 8508A is shown in the following application note from Fluke (page 7):

http://support.fluke.com/Calibration-Sales/download/asset/2114953_a_w.pdf

[quarks]

I do not know why this is causing discussion here, but as an owner of several 8.5 DMMs I have made comparisions between them and the 8508A is by far the most stable instrument and does indeed do not need ACAL. Also it is within 2ppm accurate within only about 2min. For me, this alone makes it my favorite DMM, as I do only run my 10V Ref. 24/7. There are a lot more things which makes the 8508A remarkable and most likely better than any other metrology DMM available.

But of course there are downsides to a 8508A. First of all is the price, which is more in the range of 24k$ (with option1) in the US and above 20k€ in Europe and there is no artifact cal (which makes it even more pricý, because you cannot calibrate it in a homelab, even if you have the very best calibrator i.e. like my Wavetek 4808 or Fluke 5720/5730).

Therefore for hobbiest like us, there is nothing better available then a 3458A, because of its exceptional linearity, artifact cal and ACAL function (which compensates very good for temp changes). So all you need besides a working 3458A is a good enough 10VDC reference and a as stable as you can afford 10K resistor to recalibrate it any time (exception of course is AC calibration with SCAL).

[TiN]

quarks
I think this topic brought up by lack of on-hand experience on 8508A. We see many of us run number of tests with 3458A (memory brings excellent Dr.Frank test data experiments), but I hardly recall any datalogs from Fluke box. Best part of 8508A on paper for me is it's ohms features and ratio abilities if one has Opt1 with rear ports.

[ManateeMafia]

Who has the $$$ to pony up so this can be rented? 

http://www.transcat.com/fluke-8508a-reference-multimeter-for-rent

[TiN]

Alright, back on topic.

Yey, it's alive...Well, it powers on with donor A5. However, it would be too easy to repair, don't get happy too fast. See that ERR?
I guess we lucky again, dreaded ERR 114 haunting us in this box too. Last time that eaten over 200 hours... Not expecting this to be any easier, while still there is a hope that issue somewhere not in U180. But chances are slim. 





It's a balanced rundown convergence, not the multislope rundown convergence one, which I had most issues with.
Any measurement with slow slope speeds fail faster than a second. NPLC 0.001 works, so we know what to do.
ST fails ofcourse, instantly after 10V test. Can't read 10VDC gain/timeouts.





For further tests another donor A3 was used, so we can check other boards first. With that board we can get some readings on input signals, such as 5VDC and 5VAC.





But on 100VAC and 1kVAC ranges it reads junk:



Resistance checks:





Current checks:





Somebody still believed in miracles and was thinking it would be easy 2-evenings fix? 
Can't be so naive. 

[Kleinstein]

The 100 V and 1000 V range not working has at least a common part with the divider. So these faults are likely related. This fault is likely relatively easy to fix, and even if not - still a useful unit without those ranges. So this error can wait to get fixed.

I am afraid with those badly broken units from ebay or similar source, chances are high to find a bad U180, as there seem to be quite some of these boards around. At least now we know where to look for trouble. As far as I remember a more obvious point pointing to trouble with U180 was a drift in the +- reference generated with resistors inside U180. These voltage are a good test-point anyway.

Balanced rundown could also be a more general problem with the convergence - so could still be something else than U180, like the comparators.

[TiN]

Exactly what I'm thinking too, Kleinstein.

Had trigger BRC errors from bad reference +12/-12V voltages on ADC before too when I was messing up with drifty A3 on my first unit, which had no MSRC error. So that's what my hope is, that BRC is due to something else.

I don't worry about high-voltage ranges much right now either. But I don't agree on approach leaving unit half-repaired with faulty ranges. Full function repair or nothing, otherwise why bother?

So the cliff-hanger here is if and when we get ADC working properly. Rest stuff is doable relatively easily.

[TiN]

3458A A5 outguard controller PCBA (P/N 03458-66505 Rev.B, made in 1995) from eBay seller vloutlet13 arrived.
Time to swap NVRAMs on it, upgrade FW to 9.2 and have it installed into meter 
Was it a cheapie? Not quite, I was desperate, so 400$.

[TiN]

You didn't think I forgot, right?



A5 PCBA luckily is the one which I had missing photos, Rev.B. ROM is now single chip on it, rest is almost same as Rev.A. This particular one made in 1995 or so. Good enough.



No criminal on the bottom except minor delamination around RAM pins due to desoldering sick NVRAMs.

ROM is 27C4002 from ST. UV EPROM, yey! I think I'll desolder it, put socket instead and erase with my bodge-UVC lamp setup and write Rev.9 FW over. According to label, it's Rev.7 now.



Can you see firmware bits in that die photo? No? But they are there 



And of course, refresh NVRAMs   
I'll plonk the board into my rusty good 3458A to test, so we can make sure it's good and close A5 issues once and for all.
This will be first time I open 3458A since 24/7 operation from spring 2016. I'll use a chance to blow some dust out.

[TiN]

No problems encountered  .



I think we can use my old A5 in 3458U2 instead for now. Calibration not lost on digital board swap. External LTZ1000 reads 0.01ppm within pre-swap value.

[Nuno_pt]

It's starting to look promising the fixes.

Maybe few parts then first thought.

[TiN]

Em, I think you confused a bit.

This is my good 3458A, not the U2. Just check to make sure that A5 from eBay is good and has no problems. So of course it's self-test passed.
Doesn't mean that we will see this message on 3458-U2 any time soon though.

[TiN]

Alright, seems no major issues with A1 yet, with use of good A3 board as temporary swap.



This project will soon turn into long-waiting one though, to get A3 replacement... I still can use drifter-A3 to do some tinkering though. 

[TiN]

Btw, in case someone wondered what A3 boards are installed in new meters or serviced in.

Here's photo of one from KS site:



Obviously, Keysight ran out of the control gate arrays chips for A3, so they bodged in patch board with ALTERA CPLD with bunch of 3.3V-5V level translators and pair of LDOs on top of the old board footprint. 
Mark my word, in few years from now this A3 board will be even more patched up. 

[ManateeMafia]

There's almost enough room for a Pi Zero. 

Looks like they are battling to get a replacement meter to market before it's too late.

[plesa]

Mark my word, in few years from now this A3 board will be even more patched up. 

For 27 years old instrument it is quite good, I must say. A5 board is already redesigned.
It is good start to design new instrument   With production between 700-1000 units per year the amount of components and investment is still in acceptable level until U180 became obsolete and not available....
I'm still curios how long they are going to support 3458A ( in EU are min 5-7 years from production stop).
The info on website is also good and give opportunity to order 3458A in Europe after RoHS deadline
Notice for European Union Customers: This product is not updated to be EU RoHS compliant. Please contact Keysight Authorized Distributors for quotation and ordering. Keysight will continue service and support to the end of worldwide support life.

[VintageNut]

There's almost enough room for a Pi Zero. 

Looks like they are battling to get a replacement meter to market before it's too late.

If you read the volt-nut email group, one of the participants states that all of the HP brains that designed the 3458A are no longer at KS. 

[saturnin]

Keysight has been working on a successor of 3458A for quite a while and it is a real challenge for them as they mentioned in this webcast (listen from 46:00 to 47:40):

http://www.keysight.com/main/eventDetail.jspx?cc=GB&lc=eng&ckey=2689915&nid=-11143.0.00&id=2689915

[VintageNut]

Keysight has been working on a successor of 3458A for quite a while and it is a real challenge for them as they mentioned in this webcast (listen from 46:00 to 47:40):

http://www.keysight.com/main/eventDetail.jspx?cc=GB&lc=eng&ckey=2689915&nid=-11143.0.00&id=2689915

Thank you for the link. I listened to that segment. I heard them say that they were trying to make a better one and have not been successful yet. I did not hear that they were designing a replacement for the 3458A.

In fact, they never said that they have designed a new up-to-date style instrument that is as good as the 3458A.

[Dr. Frank]

Keysight has been working on a successor of 3458A for quite a while and it is a real challenge for them as they mentioned in this webcast (listen from 46:00 to 47:40):

http://www.keysight.com/main/eventDetail.jspx?cc=GB&lc=eng&ckey=2689915&nid=-11143.0.00&id=2689915

I know that passage very well, guess who this "Frank" was, who posed that question..
My question was about an updated/improved specifications for the existing instrument, as it's known, that many improvements had been done (40k reference for example).
They answered in that manner, I think they did not really catch my intention.

I also was under the impression, that they were NOT working on a successor, and their statements even emphasized my idea, that they in fact do not have budget, brain and knowledge to even make an updated copy of that design.
Very probably, there  is no market at all for such an instrument, not to talk about the R&D cost, that will never be rewarded, even over many years.

I asked Scott Stever directly (former PM for the 34465/470A and engineer on the 3458A), and he simply refused to make any word about plans of re-design... at that instance, I had the very same feeling.

For me as a PTN manager in a big electronics company , it is really a miracle how they are still able to produce that unit with all these ancient component technologies and so many obsolete parts.

Frank

[VintageNut]

Keysight has been working on a successor of 3458A for quite a while and it is a real challenge for them as they mentioned in this webcast (listen from 46:00 to 47:40):

http://www.keysight.com/main/eventDetail.jspx?cc=GB&lc=eng&ckey=2689915&nid=-11143.0.00&id=2689915

I know that passage very well, guess who this "Frank" was, who posed that question..
My question was about an updated/improved specifications for the existing instrument, as it's known, that many improvements had been done (40k reference for example).
They answered in that manner, I think they did not really catch my intention.

I also was under the impression, that they were NOT working on a successor, and their statements even emphasized my idea, that they in fact do not have budget, brain and knowledge to even make an updated copy of that design.
Very probably, there  is no market at all for such an instrument, not to talk about the R&D cost, that will never be rewarded, even over many years.

I asked Scott Stever directly (former PM for the 34465/470A and engineer on the 3458A), and he simply refused to make any word about plans of re-design... at that instance, I had the very same feeling.

For me as a PTN manager in a big electronics company , it is really a miracle how they are still able to produce that unit with all these ancient component technologies and so many obsolete parts.

Frank

I knew that was you. I agree with everything you state except the size of the market. It is a very large market for just that one instrument.

[plesa]

It is a very large market for just that one instrument.

With 700-1000 units per year...?? We will see... But it looks that market for 8.5 DMM is small.

[Dr. Frank]

I knew that was you. I agree with everything you state except the size of the market. It is a very large market for just that one instrument.

That's to be discussed .. let's go:

They usually sold / still sell about 2000 units per year, that's about 20M$ turnover/year.
The BOM cost is quite high, as would be a re-design, with probably improved features, also HW ones.
I guess that it needs a decade to make the return-on-invest.
KS nowadays is completely cost driven, whereas in the 1980ties, the Cold War financed each of such exceptional projects.

So I really doubt that..
Other estimates and opinions, please!

Frank

[dr.diesel]

We'll have to rely on Keithley, <4PPM DMM8510, 

[plesa]

I knew that was you. I agree with everything you state except the size of the market. It is a very large market for just that one instrument.

That's to be discussed .. let's go:

They usually sold / still sell about 2000 units per year, that's about 20M$ turnover/year.
The BOM cost is quite high, as would be a re-design, with probably improved features, also HW ones.
I guess that it needs a decade to make the retrun-on-invest.
KS nowadays is completely cost driven, whereas in the 1980ties, the Cold War financed each of such exceptional projects.

So I really doubt that..
Other estimates and opinions, please!

Frank

I will reduce the amount of units sold per year, based on serial numbers it is less.
If I will be in marketing department I will try to support current 3458A as long as possible. Thats what we can see (A3 piggy back boards, A5 redesign).
That require relatively small amount of money than investing into the completely new product from scratch.
I suppose that everything depends on availability and manufacturing process for U180 ASIC.
In Europe it can be tricky next year, because unit is not RoHS compliant, but we do not know what is not RoHS compliant.
It it is components like VFD, it is possible to make replacement  and make 3458A available in Europe again. Maybe in EU they will sell used units only
But if non RoHS components is for example U180, it can be difficult.

Sorry for off topic.