Teardown, Repair & Upgrade of an Agilent 3458A 8.5 Digit Digital Multimeter

[Hugoneus]

You can watch the video here: [48 Minutes]
youtu.be/1yWjT6b1wWI

The Signal Path
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[Dr. Frank]

Hi Shahriar,

Very nice fault finding and repair.
Welcome in the 3458A club... and maybe you're turning into a volt-nut also.

How did these initial calibration errors vanish?
Have you successfully copied the content of the CAL RAM, or did you do any kind of provisional calibration?

7ppm difference to your 7510A is very good, already.
There's sort of a calibration sticker on the 3458A, with Jan 2018, or so, maybe calibration was still valid, or 1 year old, only.
So the 3458A might be less uncertain, than your 7510A, meanwhile.

Frank

[Hugoneus]

...
Very nice fault finding and repair.
Welcome in the 3458A club... and maybe you're turning into a volt-nut also.
...

My next repair is about a GPS assisted OCXO 10MHz reference and its comparison with a Rubidium source. My 'nut' related problems are growing! Wait, that doesn't sound right... 

Somebody save me... 

[Dr. Frank]

...
Very nice fault finding and repair.
Welcome in the 3458A club... and maybe you're turning into a volt-nut also.
...

My next repair is about a GPS assisted OCXO 10MHz reference and its comparison with a Rubidium source. My 'nut' related problems are growing! Wait, that doesn't sound right... 

Somebody save me... 

Well, too late, obviously..

I'm curious, how you will do the comparison, and which uncertainty of the Rb standard you'll achieve.

By chance, I'm just preparing  some photos of my old lab @ university (1989 vintage 3458A) , and my actual basement lab.
There'll also be a picture, which shows a Rb / GPSDO comparison, but how NOT to do the calibration, in fact.. 

Frank

[TiN]

I wish video be longer  . Also one thing to consider (but too late, because you already got meter calibrated) is to reduce oven temperature of the LTZ reference, to get better annual drift for the meter. But likely you don't care that much if it's 2ppm/year or 8ppm/year, unless you run meter 24/7 doing measurements, like some of us here.

How did these initial calibration errors vanish?
Have you successfully copied the content of the CAL RAM, or did you do any kind of provisional calibration?

He mentioned that Alltest did sponsor partially for pro calibration, so I'd assume meter was sent to cal lab at some point after the fix.

..3245A and improve reference on it..

I wonder where Shahriar got that idea to pimp HP 3245A from, he-he. This source is quite interesting, only drawback of it is lack of resolution (not accuracy).

[Hugoneus]

I wonder where Shahriar got that idea to pimp HP 3245A from, he-he. This source is quite interesting, only drawback of it is lack of resolution (not accuracy).

Yup! And a few other additions if time allows.

[Kleinstein]

With such an old reference / meter, I would not change the temperature.

The lack of dirt inside can be in part due to the air filter many other instrument are not using. There is also a chance the meter was used in a clean environment.

With a meter that was not on for a long time, one should check the input filter first, before powering up: There is a chance it might blow the first time you power it up.

[TiN]

It may also blow up later during operation as well, so that would be urgent candidate for replacement too. Thanks for reminder. 

[Kosmic]

So in the video Shahriar is saying that precision electronic should not be touched with bare hands.

What is the rules of thumbs about that? What can you and can't touch with your bare hands? I guess every circuit that is high impedance should be kept relatively clean.

[TheSteve]

Shahriar, is there a reason you chose to use battery backed memory for the memory upgrade?

[guido]

Great video as always.

I was only wondering about the IC sockets you are using. Not the round ´turned pin' type, but regular cheaper sockets. I would not use those in such an instrument. Actually i would only use those for 'disposable' test PCBs.

[coromonadalix]

to touch bare hand sensible electronics is a no no, the skin oil  etc .. may create problems, i use nitrile gloves ...  when at my job i touch a ultra clean gold plated pcb with no added parts on it, it leaves residues i have to clean the pcb with special cleaner to be sure there is no contaminant, because it may interfere with the solder paste we apply with silkscreen.

[chickenHeadKnob]

I wish video be longer  . Also one thing to consider (but too late, because you already got meter calibrated) is to reduce oven temperature of the LTZ reference, to get better annual drift for the meter. But likely you don't care that much if it's 2ppm/year or 8ppm/year, unless you run meter 24/7 doing measurements, like some of us here.

He mentioned that Alltest did sponsor partially for pro calibration, so I'd assume meter was sent to cal lab at some point after the fix.

Isn't alltest that company in New Jersey with the shady practices? I don't think I would buy any "for parts" unit from them. Their deal with Shahriar looks like a clever marketing ploy to get a new round of gullible buyers. They could have gifted him with a special unit which would make it appear fixing them is much easier that it usually turns out to be.

[BravoV]

So in the video Shahriar is saying that precision electronic should not be touched with bare hands.

What is the rules of thumbs about that? What can you and can't touch with your bare hands? I guess every circuit that is high impedance should be kept relatively clean.

What about the burst of mist of saliva as he speaks probably in front of the board during the video shoot ?

To proof it, just stand quite near a window glass and speak normally, you will easily see specks or tiny spots spread at the clear glass.

[Samogon]

I wish video be longer  . Also one thing to consider (but too late, because you already got meter calibrated) is to reduce oven temperature of the LTZ reference, to get better annual drift for the meter. But likely you don't care that much if it's 2ppm/year or 8ppm/year, unless you run meter 24/7 doing measurements, like some of us here.

He mentioned that Alltest did sponsor partially for pro calibration, so I'd assume meter was sent to cal lab at some point after the fix.

Isn't alltest that company in New Jersey with the shady practices? I don't think I would buy any "for parts" unit from them. Their deal with Shahriar looks like a clever marketing ploy to get a new round of gullible buyers. They could have gifted him with a special unit which would make it appear fixing them is much easier that it usually turns out to be.

Yes they are.
But for easy repair i would not be so confident, it is always looks pretty simple to follow experienced guide. And when it gets in your hands, you can easily spend tens of hours in wain.

[Kosmic]

I wish video be longer  . Also one thing to consider (but too late, because you already got meter calibrated) is to reduce oven temperature of the LTZ reference, to get better annual drift for the meter. But likely you don't care that much if it's 2ppm/year or 8ppm/year, unless you run meter 24/7 doing measurements, like some of us here.

He mentioned that Alltest did sponsor partially for pro calibration, so I'd assume meter was sent to cal lab at some point after the fix.

Isn't alltest that company in New Jersey with the shady practices? I don't think I would buy any "for parts" unit from them. Their deal with Shahriar looks like a clever marketing ploy to get a new round of gullible buyers. They could have gifted him with a special unit which would make it appear fixing them is much easier that it usually turns out to be.

Yes they are.
But for easy repair i would not be so confident, it is always looks pretty simple to follow experienced guide. And when it gets in your hands, you can easily spend tens of hours in wain.

I bought a power meter "as-is" from them some time ago and it wasn't that bad. Shipping was a bit high but the description of the item was accurate

From what I saw from their ebay listing they tend to add a lot of details (they do more than power-up test). But shipping is always expensive (to Canada at least).

but yeah, there's always an inherent risk when buying broken/as-is equipment.

[lukier]

Isn't alltest that company in New Jersey with the shady practices? I don't think I would buy any "for parts" unit from them. Their deal with Shahriar looks like a clever marketing ploy to get a new round of gullible buyers. They could have gifted him with a special unit which would make it appear fixing them is much easier that it usually turns out to be.

Yup, it seems an old 3458A is very cheap way for them to improve their public image.

I never really bought anything from them because most stuff they list are not a bargain by a long shot and they have completely random shipping costs.
I was seriously considering buying some LeCroy WaveLink active probe tips, 3 pcs for $300 or something similar, but the shipping to the UK was $450.26 (these things are very lightweight, probably 200g for the lot).
When I asked about why the shipping cost is so outrageous they've said they can ship with USPS and asked me to buy it now and they will revise the shipping costs later (and they didn't say to what amount). It all sounded very dodgy so I gave up. Why not list the shipping cost to the UK properly in the first place or do things via eBay and not some later revise gentleman's agreements, or even better, use eBay's Global Shipping scheme. Very strange company indeed.

[HighVoltage]

Hello Shahriar
You found that fault very fast, respect !

Very nice video again, thanks for sharing!

[Hugoneus]

If you have issues with AllTest’s shipping you should let them know. As far as I can see, that seems to be the biggest complaint.

Also note that I asked for a broken instrument. They could also send me a working one. But I think a repair is a more interesting video.

[lukier]

If you have issues with AllTest’s shipping you should let them know. As far as I can see, that seems to be the biggest complaint.

Their eBay listing policy is quite odd, some people here on the forum had much bigger problems than just exorbitant/random shipping costs. As I've said, even without the shipping quirks, their prices are often not very attractive for a hobbyist anyway.

As importing from the US can be expensive and/or problematic I have much lower bid threshold for uncertain sellers/listings, especially if the price is not a real bargain and the seller doesn't offer Global Shipping Programme.

Also note that I asked for a broken instrument. They could also send me a working one. But I think a repair is a more interesting video.

Sure, the video is great (I don't click on thumbs-up very often ), nice repair and you got lucky it is not the infamous drifty ADC problem which is pretty much game over. Hope to see some interesting experiments with this meter

[dr.diesel]

Isn't alltest that company in New Jersey with the shady practices? I don't think I would buy any "for parts" unit from them. Their deal with Shahriar looks like a clever marketing ploy to get a new round of gullible buyers. They could have gifted him with a special unit which would make it appear fixing them is much easier that it usually turns out to be.

Yup,

https://www.eevblog.com/forum/metrology/datron-4910-on*bay/msg1128954/#msg1128954

[mbless]

Isn't alltest that company in New Jersey with the shady practices? I don't think I would buy any "for parts" unit from them. Their deal with Shahriar looks like a clever marketing ploy to get a new round of gullible buyers. They could have gifted him with a special unit which would make it appear fixing them is much easier that it usually turns out to be.

Yup,

https://www.eevblog.com/forum/metrology/datron-4910-on*bay/msg1128954/#msg1128954

Oh wow, so Alltest is express_test on ebay?

Concerning TSP, does anybody know what the little 5V reference is that Shahriar uses?

[dr.diesel]

Concerning TSP, does anybody know what the little 5V reference is that Shahriar uses?

One of these variants:

http://www.voltagestandard.com/DMMCheck_Plus.html

[plesa]

Wauu respect for such fast repair. My convergence error ended up with A3 board replacement.

[BU508A]

Shahriar,

thank you very much for this interesting video.   

You can watch the video here: [48 Minutes]
youtu.be/1yWjT6b1wWI

I would have been really appreciated, if the video had another 12 minutes or more, so it could be sponsored by Patreon. It'll be really worth it imo.

 

Looking forward to your next video.

Thanks,

Andreas