Author Topic: Repair worklog : Old rusty HP 3458A (Read 258677 times)

VK5RC · « **Reply #525 on:** March 08, 2016, 09:22:45 am »

How about temperature management of the biological in the room? 30C for a human is too hot for a work environment. Cool the room, the human and the 3458.
A few bits of test gear , a PC will add to thermal stress for all. (HIHI)

alanambrose · « **Reply #526 on:** March 08, 2016, 09:56:19 am »

Actually I don't think the filter does that bad a job. My ~25 year old meters are very clean inside. There could be scope for a more intelligent fan control though to reduce the overall meter tempco - I'm getting +-0.3 ppm/K (see image below).

TiN - was the LTZ ref that you put in the 3245a conditioned already? - I read in a 3458a service note that Agilent would recondition A9 boards by powering them up for for 6 weeks if they had been in the parts bin for too long. My drifty 3458a seems to have sorted itself out after leaving it on for 5 weeks already and updating the 8051 to V ,2.

MM - maybe this is worth trying for your drifty 3458a?

Note in the graphic below that the regression model (using all 3 factors - the biggest being tempco) gives a predicted reading very close to the actual reading - a fairly useful characterisation if you wanted to intelligently trim the 3458a.

A.

TiN · « **Reply #527 on:** March 08, 2016, 10:03:20 am »

Well, yes, filter does the job, just need to be cleaned periodically. It's not really an issue for stock 3458A's with their scorching A9's, but could be a problem for ones at lower thermostat point.

I had 3245A running for month or so 24/7 prior that measurement. I'll have to redo it again next time.

MM's meter (opt2) got sorted out as well, after about 2 weeks running, so that info about right.

P.s. i'm travelling atm, and with Murphy's law same time ISP borked IP mapping, so can't link any data just yet, sorry.

Dr. Frank · « **Reply #528 on:** March 08, 2016, 10:28:54 am »

Quote from: alanambrose on March 08, 2016, 09:56:19 am

TiN - was the LTZ ref that you put in the 3245a conditioned already? - I read in a 3458a service note that Agilent would recondition A9 boards by powering them up for for 6 weeks if they had been in the parts bin for too long. My drifty 3458a seems to have sorted itself out after leaving it on for 5 weeks already and updating the 8051 to V ,2.

This effect only applies to the original HP references, running at 90°C.
As discussed in the Super-LTZ1000 blog, the LTZ probably encounters hysteresis effects at elevated temperatures, maybe higher than 70°C.

So, any pimped 3458A reference (100k in parallel to the 15k), or any DIY LTZ1000, running at 45..65°C, won't have this problem.

Keysight copied this problem into their 34470A reference, btw.

Frank

TiN · « **Reply #529 on:** March 08, 2016, 10:35:37 am »

I still think that was a deliberate decision to favor industrial environment specs with +50 ambient and tight rack fill. During my repairs on K2001 I had RTD on current shunt not far from A/D and with chassis closed it gets to ~62C, and that's just unit sitting on the shelf.

Dr. Frank · « **Reply #530 on:** March 08, 2016, 10:59:18 am »

Quote from: TiN on March 08, 2016, 10:35:37 am

I still think that was a deliberate decision to favor industrial environment specs with +50 ambient and tight rack fill. During my repairs on K2001 I had RTD on current shunt not far from A/D and with chassis closed it gets to ~62C, and that's just unit sitting on the shelf.

That's correct, calculation is: T(oven) = 55°C (Tamb)+ 10°C (A-version) + 13°C (Temp. rise inside 3458A) +10°C (Temp. rise in a rack) + 5°C (regulation margin).

Anyhow, the 3458A was originally promoted as a Metrology grade instrument, so they could have offered a metrology version with limited ambient temperature range of 15..35°C, like 732Bs and 8508As, and they could have used the non-A version, giving a max. oven temperature of 65°C, avoiding a lot of problems and making the reference much cheaper.

In the 34470A, the inner temperature is at least 10°C lower than in the 3458A, so they could have used an LTZ1000 at about 75°C, at 2ppm/yr. stability, quite easily.

But they just did not think new, obviously, they just copied.

Frank

plesa · « **Reply #531 on:** March 10, 2016, 07:14:41 pm »

TiN donated the ASIC from drifting A3 board for extreme teardown.
Chip is now naked and ready for following actions.
Please post your areas of interest.

TiN · « **Reply #532 on:** March 10, 2016, 07:38:06 pm »

Mm, minor correction, it's ASIC with Error 114, multislope convergence errors, the from first A/D board.

Looking forward for the photo p0rn

Perhaps analog IC design guru's can tell us more once hires pics done.

chinapp · « **Reply #533 on:** May 01, 2016, 02:31:04 pm »

is there any news of the ASIC research? i am keep watching ... $:=\$

plesa · « **Reply #534 on:** May 13, 2016, 05:27:09 am »

Quote from: chinapp on May 01, 2016, 02:31:04 pm

is there any news of the ASIC research? i am keep watching ... $:=\$

Yep, it is in pipeline with LM399, MAB399 reference and waiting for LT-FLU. Stay tunned.

Someone interested, it looks like A1 board missing
http://www.ebay.com/itm/HP-Agilent-3458A-Digital-Multimeter-For-Parts-Only-As-Is-/162067493629?hash=item25bbf9b2fd:g:dCMAAOSwWntXM1Zr

TiN · « **Reply #535 on:** May 13, 2016, 12:21:06 pm »

Yah, now it will skyrocket in price

no second 3458 for tin...

plesa · « **Reply #536 on:** May 13, 2016, 06:18:02 pm »

Quote from: TiN on May 13, 2016, 12:21:06 pm

Yah, now it will skyrocket in price no second 3458 for tin...

We will see, A1 board isnt cheap at all. Look that meter is in good shape, if we can call it meter without A1:)

TiN · « **Reply #537 on:** May 18, 2016, 04:20:27 pm »

Someone won it for rather high price at 1.6K. Perhaps EEVblog effect of posting a link here. If buyer have good A1 board and ready for some gamble it's still can be a worthy win, but these are big if's. Hopefully we may see a thread about it here or elsewhere.

TiN · « **Reply #538 on:** August 05, 2016, 06:32:53 pm »

Rusty 3458 found it's glory. Ebay seller stolen my photo for the listing: http://www.ebay.com/itm/HP-Agilent-3458A-Digital-Multimeter-8-8-5-Digit-DMM-/262563138089?hash=item3d21fb8a29:g:AqsAAOSwnQhXo1zD

Drawback of not having watermarks all over the photos.

pelule · « **Reply #539 on:** August 05, 2016, 07:24:33 pm »

As your pictures are high resolution and good quality, it may happen, if one searches for a pictures of a specifc gear on the web.

And it tell's a lot regarding the quality of the gear offered...

But please do not stop your style of publishing

- a bunch of interest her.
PeLuLe

Monittosan · « **Reply #540 on:** August 07, 2016, 11:56:56 pm »

Quote from: TiN on August 05, 2016, 06:32:53 pm

Rusty 3458 found it's glory. Ebay seller stolen my photo for the listing: http://www.ebay.com/itm/HP-Agilent-3458A-Digital-Multimeter-8-8-5-Digit-DMM-/262563138089?hash=item3d21fb8a29:g:AqsAAOSwnQhXo1zD

Drawback of not having watermarks all over the photos.

His sold 4 of them in the past. I guess they where all from that lot?

TiN · « **Reply #541 on:** October 18, 2016, 12:31:50 pm »

Hmm, what's going on here...

Nuno_pt · « **Reply #542 on:** October 18, 2016, 12:34:27 pm »

Hmm, it smells like RAM/EEPROM's replacement.

ElektroQuark · « **Reply #543 on:** October 18, 2016, 02:10:04 pm »

A DIP14 swimming in an DIP 28.
Waiting for the "teardown"...

TiN · « **Reply #544 on:** October 18, 2016, 02:44:50 pm »

No, these are fresh new parts

SeanB · « **Reply #545 on:** October 18, 2016, 07:28:16 pm »

DIP14 is the small CMOS memory controller made by Dallas, which is the heart of all those timekeeper and RAM modules. It is just there on one side of the PCB inside, with the other side having the 6116LP3 RAM and the RTC chip and then stacked over all this the small lithium primary cell and the backup cell if fitted. The chip does the power off function, switching Vcc and keeping all the enable pins in a correct state when power falls, so the RAM will not draw excess power during standby.

VK5RC · « **Reply #546 on:** October 18, 2016, 11:37:53 pm »

My 2 guesses
1Are you about to do some experimentation looking at the effect of different timing of the different models of dallas nvram?
I recall when looking for a replacement for mine, the original was hard to find, ended up getting a few 'close' ones, I don't recall the part numbers now.
2 You are about to grind off the top and get to the lithium connections?
Robert

TiN · « **Reply #547 on:** October 19, 2016, 04:21:31 am »

No and no. You guys such savages

.

One local taiwanese volt-nut contacted me few days ago. After some challenging discussion with great help of google translate, it was determined that he has some nice gear, including a RAM-sick 3458A. So hopefully next month we will have a chance to meet and look on his 3458A, and perhaps get my 4920M calibrated. This is my best shot right now for AC calibration.

klaus11 · « **Reply #548 on:** October 19, 2016, 05:32:25 am »

A little help please, I need to know if this new firmware upgrade lose calibration data. From a very early version up to 8.2 example.

Dr. Frank · « **Reply #549 on:** October 19, 2016, 05:42:51 am »

Quote from: klaus11 on October 19, 2016, 05:32:25 am

A little help please, I need to know if this new firmware upgrade lose calibration data. From a very early version up to 8.2 example.

No.

Frank


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Author Topic: Repair worklog : Old rusty HP 3458A (Read 258677 times)

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