agilent 3458A multimeter value

[TiN]

This thread motivates me to dig into my Keithley's trying fix some
Reversing schematics. Layout is not reverse-friendly at all 

[eurofox]

This thread motivates me to dig into my Keithley's trying fix some
Reversing schematics. Layout is not reverse-friendly at all 

You are right, I get adicted to it and this particular instrument is quite unique, was designed 25 years ago and nothing really to replace it.

From time to time I buy from ebay defective instrument at very low cost and fix them.

[eurofox]

Hello Vot Nuts,

Today I got the 2 missing NVRAM .... after 2 long weeks waiting 

The good news is  it is working 

And a few other picture from inside the instrument like requested.

[eurofox]

Some more pictures

[quarks]

congratulations 

[Dr. Frank]

Calibrate and have fun! 

Frank

[ManateeMafia]

Congratulations.

Not a bad deal, a scope for a 3458A. It doesn't get much better than that.

Your zener reference could take a few weeks now to get stable. If you calibrate it now, you should compare it against your 10V reference every day until the readings remain fairly constant.

It took several weeks before my meter would stay close to zero with the inputs shorted with a copper wire across the inputs. I ran ACAL ALL a couple of times a day for several weeks, and I could see the zero drift less with each passing week. Temperature is also a big factor too. This thing is very sensitive to temp changes, even by a change of 1 deg. C

[eurofox]

The scope is an Agilent 500Mhz combi scope with all probes like new. I bought it because it was a good deal, I already have 4 scopes.

If I could not get the instrument working it was a very bad deal, I can say that the deal is fair for a working instrument.

I still have minor problems discovered with testing it, the keyboard key's 1234 are not responsive, 2 not responsive at all.

I'm afraid they use keys with carbon on the rubber key making a short on the pcb, maybe I'm wrong but will have to check it, but I suppose that Agilent can supply this kind of spare part.

eurofox

[Dr. Frank]

Your zener reference could take a few weeks now to get stable. If you calibrate it now, you should compare it against your 10V reference every day until the readings remain fairly constant.

It took several weeks before my meter would stay close to zero with the inputs shorted with a copper wire across the inputs. I ran ACAL ALL a couple of times a day for several weeks, and I could see the zero drift less with each passing week. Temperature is also a big factor too. This thing is very sensitive to temp changes, even by a change of 1 deg. C

That's absolutely not right, or not in that extreme, sorry.

The LTZ reference itself is stable within a few minutes. Afterwards it may drift a few tenths of ppm, or less. That's how my two external LTZ1000 behave @ 45°C.
For the 3458A it's hard to tell, how the LTZ behaves at 95°C, because normally you cannot measure the internal ref from outside, and the intial drift is determined totally by the gain resistors drift.

The 3458A as a whole only needs those 2..4h hours of warming up, 12..15°C max. difference of internal vs. room temperature.
Take care, that the difference is not greater, otherwise clean the fan filter. And put it on desk top, not in a rack for best metrological performance.

I always shut off the 3458A after a session.
When I power on again, it takes about 2h, and perhaps (not necessarily) an AUTOCAL, and then the instrument is back to a few 10nV zero reading, and Full Scale reading to tenths of ppm.
That does not take weeks, that's absolutely not correct!
Even after weeks of being shut off.

For precision measurements, half a day of stabilization is used.
Afterwards, Autocal is only necessary if Rt changes more than 1°C.

But you can measure such small effects only, if you have absolutely stable RT over a longer period of time, and if you have a source with equal or less drift than the internal one.
A Fluke 721A is not sufficient.
LM399H is minimum requirement, better another LTZ1000 or oven stabilized SZA263 (Fluke 732, 5440, 5720, 7000 etc.) reference is required.
Also a high quality short is required, either good laboratory cables, or a clean copper wire.

If the instrument is not rock stable under the described conditions, it would be faulty.

How long the Geller ref takes to stabilize, I cannot tell. But weeks would be too long, to give a reliable reading,  I think.

Frank

[ManateeMafia]

I should have been more specific. I was referring to service note 3458A-18A, where the reference may revert back to its pre-aged state if left off for extended periods.

http://literature.agilent.com/litweb/pdf/3458A-18A.pdf

The meter that I repaired came to me as a "for parts only" deal along with a second unit in much worse shape. I was able to piece together one good one out of two, but they sat for about 9 months in my possession before I  worked on them. I went through the calibration procedure using a 10V reference and 10K resistor since the NVRAMs were replaced.

I compared the fixed meter to a third that sat for about 6 months. There was a difference between the two meters. There possibly may be an unknown issue with the repaired meter, but it seemed to drift from zero a lot farther in the beginning and now it is pretty steady day to day. I leave it on 24/7 with the inputs shorted and have been patiently waiting to get a proper calibration from Agilent. I have a few other projects I am working on and my list of to-dos is getting longer.

Perhaps this service note does not apply, I am not certain, but I thought it may be at least somewhat relevant if it is unknown how long the meter sat before it was repaired.

[Dr. Frank]

I should have been more specific. I was referring to service note 3458A-18A, where the reference may revert back to its pre-aged state if left off for extended periods.

http://literature.agilent.com/litweb/pdf/3458A-18A.pdf

The meter that I repaired came to me as a "for parts only" deal along with a second unit in much worse shape. I was able to piece together one good one out of two, but they sat for about 9 months in my possession before I  worked on them. I went through the calibration procedure using a 10V reference and 10K resistor since the NVRAMs were replaced.

I compared the fixed meter to a third that sat for about 6 months. There was a difference between the two meters. There possibly may be an unknown issue with the repaired meter, but it seemed to drift from zero a lot farther in the beginning and now it is pretty steady day to day. I leave it on 24/7 with the inputs shorted and have been patiently waiting to get a proper calibration from Agilent. I have a few other projects I am working on and my list of to-dos is getting longer.

Perhaps this service note does not apply, I am not certain, but I thought it may be at least somewhat relevant if it is unknown how long the meter sat before it was repaired.

Service note 18A describes faulty references in agilent instruments (serial number beginning with "US....."), produced  just before 2007. You should find out very easily from instrument serial numbers, or PCB date codes, if that applies to your repaired instrument, or its diverse assemblies.

I don't know, which parameter you have compared against the other working 3458A, as your description is rather vague again.

As I already stated:

If zero reading and Full Scale reading against a known good reference are not rock stable after 4h warming up under stable environmental conditions, your repaired instrument still is faulty, quite obviously.

Frank

[TiN]

Congratz.

I see MV106 quite popular, lol That's all because Dave videos. 

[eurofox]

Hi Volt Nuts,

I got finally my voltage reference from Geller Lab and could calibrate the unit. I’m very happy with it. 
After final calibration when I measure the reference I get from 9,999999 to 10,000001 VDC. 
It is not too bad I think, because it is calibrate with the same reference it is what I can expect if the instrument is working well. 

I just have the keyboard to fix, I did not open it but due to the nature of the key’s I expect that it is a system like in the TV remote control where carbon is used and make a short on the PCB.

I order some repair kit with carbon.

If someone got experience with this kind of problem advice and comments are welcome.

eurofox

[Dr. Frank]

Hi Volt Nuts,

I got finally my voltage reference from Geller Lab and could calibrate the unit. I’m very happy with it. 
After final calibration when I measure the reference I get from 9,999999 to 10,000001 VDC. 
It is not too bad I think, because it is calibrate with the same reference it is what I can expect if the instrument is working well. 

If someone got experience with this kind of problem advice and comments are welcome.

eurofox

Instead of 7 1/2 Digits, you should arrange the 3458A to display/measure 8 1/2 Digits, i.e. NDIG 8, NPLC 100, and then report the stability of the Geller ref .
A good ref should be stable to a few parts on the very last digit.

Anyhow, congrats again, and have fun.

I think, the front including keypad is available as spare part from agilent, and does not cost that much.

But first inspect, if that is really the problem, perhaps a cleaning of keys and PCB is sufficinet, if a liquid had been poured over.

Frank

[eurofox]

Hello Volt Nuts,

Update of repair of my HP3458A

I got the carbon glue yesterday, in fact I order "Keypad fix" and "Wire glue" and they are both very similar, produced by the same company.

I did some test on paper and gummy and test the flatness and the resistance, I’m very surprised that this stuff is conducting very well.
Finally I decided to use the “Wire glue” and it is anyway indicated that it can be used to repair gummy keys like keys from a remote control as well.

After removing the front panel (tricky) and opening the keyboard, cleaning all keys on both side the PCB and the gummy part I add a very thin coating of carbon glue on all keys not only the few “bad” keys.

All keys are working now perfectly. 

I add extra RAM for option 1. 

The instrument is working well now without errors anymore. 

I have decided to send it to Agilent to calibrate it correctly, DC and resistance is ok after calibration with a DC reference and a 10k resistor but AC is not really accurate anymore compared to my 6 ½ digits that is calibrated.

This ways I will have a rock solid AC/DC/Resistor reference in my lab because of the age of the instrument it will not drift much anymore.

On ebay the prices are getting up all the time from US$3000 to more than US$6000, it is a good investment

I’m working on a 10V DC reference based on the LTZ1000A, I’m just curious to compare it to the Geller Lab module.

eurofox

[rjyousey]

We have a nice 3458a for $3850 usd with opt 001 and 002, it was recently checked by a high end cal and repair lab, sold and returned because with a blown current fuse.  We have since replaced the fuse and retested the unit.  908-328-3663

[eurofox]

My 3458A is on he's way for calibration in Agilent lab.

I'm curious to check the Geller Lab reference compared to the new calibration.

I will be able to check and correct my own calibration tools 

eurofox

[texaspyro]

A local contract assembly house was shutting down their operations and yesterday there was a liquidation auction.  One lot was a new-ish Agilent 3458A (option 002) that has been kept under a maintenance contract.   It passed self-tests and ACAL.   I had a nice talk with their lead tech and he gave me the history.  $2000 later and it's mine (I didn't really need a fourth one, so I low-bid it... will wonders never cease).  I also got a HP-58503B GPSDO.

They also had a second 3458A in a lot of 50 pieces of test equipment in their "to-be-repaired / calibrated" cage.   It had a sticker on it "Do not use, readings inaccurate". I bid $500 on the lot, but it went for $1500.  There was a lot of nice stuff in that lot (and some crap)... I should have bid more.  I had a guy lined up who was willing to load and remove all the equipment in exchange for anything I did not want to keep.