Author Topic: Agilent 3458A Repair  (Read 6957 times)

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Offline IanJ

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Agilent 3458A Repair
« on: July 09, 2018, 08:42:33 am »
Hi all,

I broke a major rule with this purchase. I was contacted out of the blue from somebody I didn't know who said they were selling a 3458A located 1000's of miles from me overseas. Normally one would run a mile but I decided to humour the guy and asked for photos, then more photos and more of an explanation.

They said they had powered it up with the AC selector in the wrong position and blew up the power supply. It's fixed now apparently and one of the photos he did send me showed it powered up, "ISOLATOR FAILURE" on the display. They said one of the optic cables melted during the power supply issue. Internal photos I received showed the cable missing.
The story of the power supply failure looked like it might be true as some of the rectifier diodes looked like they had recently been changed out.

So I kinda knew there was no way I was buying it, even if faulty, drifty etc etc it would still be worth a lot................and I couldn't/wouldn't insult them by offering a pittance, but eventually they gave me a price.......600 USD (£452).
They wanted payment by PayPal and after a good lot of checking including contacting PayPal direct I understood I was completely covered as the buyer even if a bunch of bricks in a box arrived..........so I went ahead and bought it!

It arrived today, here's some pics. NB. I have fitted a replacement fibre cable already (I purchased from AB ahead of today).

The only thing I see it's missing is the rear fuse holder.

So now I am hoping for guidance from you guys on how to proceed with power up........I don't know much about 3458A internals, just the basics (I do have my own HP 3458A).
I am thinking power up with the psu outputs pulled etc etc........but please give me some guidance.

PS. I do have the bottom shield and covers, just removed for the pics.

Ian.











« Last Edit: July 09, 2018, 08:47:11 am by IanJ »
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #1 on: July 09, 2018, 09:48:55 am »
 :-+ Sounds like the very story of my first rusty friend : https://xdevs.com/fix/hp3458a/.
You looking at 400$ for transformer. Even then at 600$ this deal is "buy first, ask questions later".

If you feeling it's too much for you, I can help you to get rid of the meter, even pay double for it. Like TheSteve say, i have no limits to my greed.  >:D

Isolator failure means analog power is missing/broken or CPU cannot communicate with A3 ADC MCU over the fiber. If transformer is melted due to overload, then inguard power could do all kind of fun to the analog boards.

Also it is strange meter, perhaps refurb unit. A6 board is still old, but rest is newer.
« Last Edit: July 09, 2018, 09:50:32 am by TiN »
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Offline zucca

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Re: Agilent 3458A Repair
« Reply #2 on: July 09, 2018, 09:53:31 am »
Congrats, nice Ferrari for your garage.

what's the brown material on the the blue elco cap 35VDC? It looks horrible.



After replacing the dead parts and the paffner AC filter, I would power up that beast slowly with an AC variable trafo, checking temperatures with an infrared camera and current absorbed.
Please consider me not a 3458A  expert, I am trying to use common sense here.
« Last Edit: July 09, 2018, 10:07:23 am by zucca »
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #3 on: July 09, 2018, 10:20:28 am »
Goo on 8200uF blue cap is just from adhesive tape. Now after second look trafo death is most probable, as same protection zeners are cooked on A4 PSU board, as they were on mine.
Easy fix after you get new transformer from Keysight. Somebody also gutted key caps for guard/terminal switch rods, those caps are indeed not original.

And if you did not take ADC A3 cover off, that part is missing too.
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #4 on: July 09, 2018, 05:40:06 pm »
Hi all,

Tests/checks/findings so far:-

1. Earth spade connector on input filter broken - Fixed, it had been soldered on and broken, so just soldered it back.
2. Top shield missing - Has anyone got one for sale PM me.
3. Fuse holder cap missing - RS looks like have the FAU fuseholders so have purchased.
4. Air filter disintegrated on removal/cleaning - Have fixed one up.
5. Transformer secondaries look intact, at least not open circuit, readings per xDevs site so far.
6. R207 - Vishay 80436 VHP101
7. NVRam Snapchat battery date codes = 942 = 2009 Week 42

Hires photos - https://www.dropbox.com/sh/krj8v3jf78fjtp0/AACW4Qkzwr9_5oM_94BtfORqa?dl=0.

No power up yet, I'll leave that till I get the fuse holder cap.

Ian.
« Last Edit: July 09, 2018, 08:15:53 pm by IanJ »
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Offline martinr33

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Re: Agilent 3458A Repair
« Reply #5 on: July 10, 2018, 12:49:29 am »
Once you are confident that the voltages are good - nyou might try switching boards into your working unit, if it is not calibration sealed.

Or - the PSU boards are nothing special, you can disconnect them, and fix them up for the correct voltages. With that done, you can get into the rest of the unit.

The ADC is recent enough that it should not have the drift issues.

There's a cap on how much you want to spend - for $2700, HP will do you a full refurb. Two boards and sundries will run you that. On the other hand, except for the ADC, the boards have common, if obsolete, parts.

One of the neat things about these units is that the processor board gets all its internal connections through a single IDC cable  - and half the wires are grounds. Lots of serial activity here, ripe for a good hack.
 

Offline IanJ

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Re: Agilent 3458A Repair
« Reply #6 on: July 10, 2018, 04:48:13 pm »
Hi all,

So my fuse cap came from RS so was able to power up......here's my findings 5mins in:-

First power up, errors straight away, either one of the following, sometimes appear after a Vdc reading appears on display, sometimes before:
System error 114 multislope rundown convergence
System error 114 balanced rundown convergence

Ignoring the above straight to first PSU checks:

Power Supply checks:-
Outguard Psu (5v) = 5.08V
Outguard C8 =   18.78v
Outguard U200 = not sure where to measure but display works so assume ok
Inguard A1 main pcb (-10v) = -9.79v
Inguard A1 main pcb (+18v) = +18.42v
Inguard A1 main pcb (-18v) = -18.50v
Inguard A1 main pcb (+5v) +4.98v

Did a quick test by applying 10.0000Vdc to input and the reading gave 10.25Vdc

If I run RESET the 3458A I may get some continious readings but then it beeps and stops updating, sometime quickly, sometimes after 10secs or so.

Running TEST I get self test failed at TEST DCV 10V and with "Error 209, Hardware Failure Timeout unable to read A/D 108"

Thermal camera images attached (after 30mins power up), the components in red are warm, to touch, some are quite warm to touch verging hot. Hottest being 43degC.

Ian.
« Last Edit: July 10, 2018, 05:29:19 pm by IanJ »
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #7 on: July 10, 2018, 05:45:59 pm »
Quote
System error 114 multislope rundown convergence
System error 114 balanced rundown convergence

Sorry to hear. Now Keysight is your only friend, with new A3 ADC board (~1300$). Very tiny chance this could be Elantec comparator, but wouldn't have hopes up.
You can indeed confirm that U180 ASIC is bad on A3 by measuring with your working 3458A reference +12, -12V and +5V voltages on A3. Example details here.
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #8 on: July 10, 2018, 06:13:48 pm »
Quote
System error 114 multislope rundown convergence
System error 114 balanced rundown convergence

Sorry to hear. Now Keysight is your only friend, with new A3 ADC board (~1300$). Very tiny chance this could be Elantec comparator, but wouldn't have hopes up.
You can indeed confirm that U180 ASIC is bad on A3 by measuring with your working 3458A reference +12, -12V and +5V voltages on A3. Example details here.

What doesn't look good is the EL2252 dual comparator as it is running quite hot, over 70degC and looking at the spec it's a 70degC IC......Hmmmm!
I will try replacing this first before I hit the schematics/scope and try to understand whats going on. I like the early gut feeling approach first......:-)

Ian.
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Offline quarks

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Re: Agilent 3458A Repair
« Reply #9 on: July 10, 2018, 06:17:56 pm »
Hello Ian,

if you have a second working 3458A you can swap A3 board and see if errors go away.
If more than on board needs to be replaced I would ask Keysight how much a full repair with calibration is.
And then decide if that is a better deal.

Good luck

 

Offline IanJ

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Re: Agilent 3458A Repair
« Reply #10 on: July 10, 2018, 06:19:47 pm »
Hi,

For now I don't want to go near my working 3458A.......it's used most days to test my PDVS2 refs.

I checked the A3 board references and they are spot on. +12v, -12v & +5v.

A few EL2252CM comparators now on order........

Ian.
« Last Edit: July 10, 2018, 06:24:25 pm by IanJ »
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #11 on: July 10, 2018, 06:47:04 pm »
I doubt they are spot on, you cannot say that without doing datalog over few hours. Read my articles, I had same issues before. Absolute value if those reference voltages does not matter, ADC working with charge, not voltage potential. What matters is the stability of those reference levels. Because they are formed by same part of U180 resistor network, drifty faulty u180 usually shows up as change in ref levels. You must use stable ppm-resolution meter to measure those, hence the second 3458. No need to take working instrument apart (!).

And before all that, drift is not the main problem with your U180 anyway. Set NPLC 0.001. Likely it will work fine for long time in fast slope mode ;).
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Online Kleinstein

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Re: Agilent 3458A Repair
« Reply #12 on: July 10, 2018, 06:55:09 pm »
These comparators use quite some power, and if  run from +-15 V they will get hot. The 70 C spec is for the environment, the case will get hotter quite a bit.

For testing U180, the point would be to measure the +12 V,-12 V and maybe the -5V and 7 V reference of the broken DMM. If these voltages (and especially there ratio) shows a significant drift (e.g. more than 1 ppm/week) U180 is likely broken. This test needs some time in between.
I see no real need to measure inside the good 3458, it's more like using the good 3458 to measure those voltages.
 

Offline IanJ

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Re: Agilent 3458A Repair
« Reply #13 on: July 10, 2018, 07:01:41 pm »
I doubt they are spot on, you cannot say that without doing datalog over few hours. Read my articles, I had same issues before. Absolute value if those reference voltages does not matter, ADC working with charge, not voltage potential. What matters is the stability of those reference levels. Because they are formed by same part of U180 resistor network, drifty faulty u180 usually shows up as change in ref levels. You must use stable ppm-resolution meter to measure those, hence the second 3458. No need to take working instrument apart (!).

And before all that, drift is not the main problem with your U180 anyway. Set NPLC 0.001. Likely it will work fine for long time in fast slope mode ;).

Ok, I read you wrong......I thought you were meaning the reference voltages would be dead if A3 board was faulty........I haven't looked at the schematic yet......and yes drift is a key aspect to look at. I am looking forward to getting it up & running and testing this.

For now I am leaving it powered down until I replace the comparitor, I am not happy to see the IC running at over 70degC.

xDevs.com is a magnificent resource, I am in and out of there all the time this past 24hrs....:-)

PS. My long term goal is to get this 3458A up & running then calibrated at Keysight, then sell one of the 3458A's (I don't need two!!!)..........and probably get a 34470A which will suit my day-to-day and workshop layout better.

Ian.
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Offline chuckb

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Re: Agilent 3458A Repair
« Reply #14 on: July 10, 2018, 08:10:33 pm »
https://www.eevblog.com/forum/metrology/repair-old-rusty-hp-3458a/msg808569/#msg808569

On TiNs thermal photographs the comparitor was running around 65 deg C.
 
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #15 on: July 11, 2018, 04:20:08 am »
Yep, those comparators running warm, it's normal. It's unlikely that newer 2252 is fail though.

Quote
PS. My long term goal is to get this 3458A up & running then calibrated at Keysight, then sell one of the 3458A's (I don't need two!!!)..........and probably get a 34470A which will suit my day-to-day and workshop layout better.
Selling sounds like a mistake to me, but who am I to tell :).

If you want to get it calibrated by KS, then whole option sending the box to them for full repair + cal begin to make sense, as you need new ADC anyway, and who knows what else.
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #16 on: July 11, 2018, 10:08:41 am »
Thanks for all your help guys so far, this is fun!

I had an hour this morning so got my isolation transformer and scope set up and started probing A3. The comparator output seems active, normally high then when run test or reset i see some activity.
Plan is to start understanding how it works and take it from there.
Last resort if i am honest is to send to Keysight for repair, i want to explore other avenues first.

Ian.
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Online Kleinstein

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Re: Agilent 3458A Repair
« Reply #17 on: July 11, 2018, 10:48:04 am »
For testing the DMM, there is no absolute need to use an isolation transformer. The inguard part is supposed to be isolated already with a high quality transformer. It would be more like using an isolation tester to check if the transformer is still OK after some possible over-voltage and thus maybe high temperature.

With the shown error messages a drifted U180 hybrid is a very real possibility, which would mean a new ADC board to repair. As TiN noted already a very fast mode might still work. If it does this would also point towards U180 trouble - other faults would likely also effect the fast mode. Looking at the drift of the +-12 V is one of the easiest ways to check.

If it still works in the fast mode, this might be used if the rest (e.g. amps, Ohms ?) still works.
 
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #18 on: July 11, 2018, 12:50:07 pm »
Kleinstein, all functions base of VDC, so from if ADC not converging properly, than none of that will work either.
I'd pretty sure Ian's ADC have FET charge switches in U180 bad as well, so drift test may not even show anything. It's just usual that when U180 goes bad, than whole thing goes haywire, not only resistor network or only FET switches (there are two dies inside U180).

I have three dead A3's , one of which drifty and two have convergence problems. One of these U180's was sent to plesa for SEM imagery, but he's busy/lost it/forgot it  :-DD.
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #19 on: July 11, 2018, 03:05:06 pm »
Set NPLC 0.001. Likely it will work fine for long time in fast slope mode ;).

Seems to run ok continiously with .001 NPLC (VDC & Ohms), then as soon as then set to 0.01 it will run for 10secs or so then stop with a beep.
NB. Cal is way off (but least of problems), 10.0000 Vdc applied, 10.19XXXX reading.

Ian.
« Last Edit: July 11, 2018, 03:08:03 pm by IanJ »
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Re: Agilent 3458A Repair
« Reply #20 on: July 11, 2018, 04:58:54 pm »
Okay, then EL2522 is working fine, and your issue are indeed sick U180. Welcome to "new A3 ADC club".  :-BROKE
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #21 on: July 11, 2018, 05:46:25 pm »
Ok folks........so I am contacting Keysight to get some options and prices. It's a pity they won't sell U180's on their own, would have been fun to replace it.........maybe they have limited qty's.

Do I get a "new A3 ADC club" badge or T-shirt...... ;D

Ian.
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Offline retroware

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Re: Agilent 3458A Repair
« Reply #22 on: July 12, 2018, 12:46:15 am »
Having just joined the 'new A3' club I can pass along my experience.

I purchased a late 1990s vintage 3458 for around $2k. Advertised as passing self test and auto cal which it did indeed do when it arrived.  The first thing I did was:

Monitored it against my relatively stable 731B
Started doing a daily CAL?72 check

Sure enough, the CAL72 value was drifting down at a fairly steady rate of around .75ppm per day. In addition, the 731B voltage was drifting up about the same rate.  Performing an ACAL would immediately drop the measured voltage down to the expected value. Thus, I was fairly sure I had the dreaded drifty A3 disease.
 
So I contacted Keysight and arranged an A3 exchange. The initial cost is $1486 but they supposedly refund $286 if you return the old board.  Good news, free shipping :)

The board was backordered for about 3 weeks, during which I continued to monitor the CAL72 value.  The drift seem to slow a bit and sometimes time flattened out but still, over 3 weeks, was out of spec with regards to the service note.

My new A3 arrived a couple of days ago and was about a 20 minute swap out. The first couple of days of CAL72 numbers are now down in the .05ppm/day range.  In addition, measuring both my 731B and 5440B confirm the stability of both of the those sources and the 3458.  So far, I'm a very happy with the replacement.

I haven't yet sent back the old A3.  In fact, there was no prepaid label or other instruction on how to do so.  Supposedly, I have 30 days to figure it out.

I would really love to know what causes these A3 units to drift.  Mine was drifting pretty darn linearly regardless of whether it was powered on or not. 

 
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #23 on: July 12, 2018, 01:21:31 am »
Quote
I would really love to know what causes these A3 units to drift.  Mine was drifting pretty darn linearly regardless of whether it was powered on or not.

This little guy is the drift reason  >:D. I spend few hundred hours trying to patch a solution to no avail:



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Offline martinr33

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Re: Agilent 3458A Repair
« Reply #24 on: July 12, 2018, 02:26:32 am »
Ian. one thing you should do is run the full autocal, if you have not done so.
 

Offline IanJ

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Re: Agilent 3458A Repair
« Reply #25 on: July 12, 2018, 05:51:30 am »
Ian. one thing you should do is run the full autocal, if you have not done so.

Well, I have tried ACAL DCV a few times and it fails at start.

Ian.
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Offline zucca

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Re: Agilent 3458A Repair
« Reply #26 on: July 12, 2018, 08:12:59 am »
Can't know what you don't love. St. Augustine
Can't love what you don't know. Zucca
 

Offline IanJ

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Re: Agilent 3458A Repair
« Reply #27 on: July 16, 2018, 10:34:55 am »
Hi all,

UPDATE:

I contacted Keysight.

Date of manufacture:- July 2009.

They say A3 boards are for internal repairs only and the 3458A needs sent to them. I am disputing this as their website claims it's orderable and offers trade-in discount...…...As far as I am aware some of you guys have purchased A3 boards from them....correct?

Ian.
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Offline quarks

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Re: Agilent 3458A Repair
« Reply #28 on: July 17, 2018, 02:42:00 pm »
Hello Ian,

I have bought an A3 board from Keysight in Boeblingen Germany a few years ago.
I do not know if they still sell any, but you can try.

good luck

 

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Re: Agilent 3458A Repair
« Reply #29 on: July 17, 2018, 04:51:53 pm »
Hi all,

Got a reply from Keysight UK and they say they are now checking with the parts team in the US to see if I am able to order the A3.

Ian.

UPDATE (18/7/18):
Got quote from Keysight UK......good to go regarding ordering the A3. It's described as a "Tested Fresh Board".

« Last Edit: July 18, 2018, 03:09:34 pm by IanJ »
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Offline retroware

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Re: Agilent 3458A Repair
« Reply #30 on: July 20, 2018, 04:32:19 pm »
As I mentioned in a previous post, I recently went through the A3 exchange process with Keysight.  All in all it was a very pleasant transaction (other than the price!). My old A3 was quite drifty as measured by CAL72.  The new unit is very stable. It has moved a total .015ppm over a two week period.

I hope your experience ends up being similar.
 
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #31 on: September 14, 2018, 02:41:31 pm »
Hi all,

Finally got around to an A3 exchange with Keysight.
Photo below old & new board side by side......and it powered up.

Have fitted the new board and powered up........my errors & lockups have gone, so now requires a bit of testing & CAL. Will leave it powered for a few days before attempting.
PS. ERR shown is because it wants an ACAL........which it's doing. Hopefully all will be fine. It's fine, all ERRs cleared.
I managed to get a bottom shield from Adrian, including the small A3 board cover....so all is there now physically.

Never thought I'd have one 3458A let alone two!, great fun!.......but the plan I guess is to sell this one at some point.

Ian.

« Last Edit: September 14, 2018, 03:21:18 pm by IanJ »
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #32 on: September 14, 2018, 03:34:18 pm »
Selling 3458 is a volt-nut capital crime. Those wrong buttons bothers me too  ;) :)
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #33 on: September 14, 2018, 03:39:47 pm »
Hi all,

Forgot to say......the filter gauze deteriorated/fell apart so am sourcing some new material to cut to size . Does anyone know what mesh size is fitted normally. I am thinking 50 or 100 mesh.

Ian.
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Offline IanJ

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Re: Agilent 3458A Repair
« Reply #34 on: September 14, 2018, 03:52:17 pm »
Those wrong buttons bothers me too

The funny thing is it's not as if it's just the rods that are the wrong size, the aperture is sized accordingly within the front panel itself.......which leaves me wondering either they were changed out at some point from some other model.......or they did indeed make a batch this size.

Can just see in the attached piccy.

Ian.

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Offline TiN

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Re: Agilent 3458A Repair
« Reply #35 on: September 14, 2018, 04:09:17 pm »
Button cap is wrong. It's a separate part.
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Re: Agilent 3458A Repair
« Reply #36 on: September 15, 2018, 01:44:52 pm »
Hi all,

Did a bit more work this afternoon, piccy attached, repaired 3458A at the top.

I have run a quick DCV CAL 0 and CAL 10.00000 using a PDVS2 as source and so far so good. Got caught out for a few mims when CAL 0 was failing, turns out I hadn't disabled the secure jumper on the cpu board.
The new Snaphat batteries I fitted are working fine.......but I did notice (per M.J.Lorton's 3458A) that the new batteries I purchased were date stamped older than the ones fitted.....but changed them out anyways.

The display is slightly brighter on the new one also, my original is an older Feb. 2000 machine after all.

PS. If I can find some button caps........I'll change them  ;)

PPS. I now have an air-con unit in my workshop so the temperature is pretty stable day & night......so will leave both the 3458A's running 24/7 for comparison.

Ian.
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #37 on: September 15, 2018, 02:13:49 pm »
I thought you had original 3458 traceable calibrated at lab?  :-//
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Re: Agilent 3458A Repair
« Reply #38 on: September 16, 2018, 12:16:30 am »
The original machine is from year 2000 but with Keysight panel

通过我的 PRA-AL00 上的 Tapatalk发言

 

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Re: Agilent 3458A Repair
« Reply #39 on: September 16, 2018, 09:13:49 am »
The original machine is from year 2000 but with Keysight panel

通过我的 PRA-AL00 上的 Tapatalk发言

I replaced it with a new front panel.......I still have the original HP one (very old looking).

Ian.
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Re: Agilent 3458A Repair
« Reply #40 on: September 25, 2018, 07:58:35 pm »
Hi all,

Playing with this 3458A and I can't get it to recognize the GPIB connection.

If I plug in the cable then RESET (keypad) on my working 3458A I will get LSTN, and the CONNECTION EXPERT on my PC will recognize address 22.
On this 3458A though when I plug in I get nothing, and I have checked the address is set to 22, and trying CONNECTION EXPERT nothing is listed either.

I did try the procedure per the service note 13A (albeit I think my A5 board is much newer) and the SRQ test passes per the note.

The GPIB connector socket looks good, no corrosion or bend pins etc.

I'm using a new 5mtr GPIB cable, but it does seem to work on my other 3458A......albeit I haven't had a chance to properly test.
I did try an 82357B (clone) and I get nothing there also.

Ideas?

Ian.
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Offline TiN

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Re: Agilent 3458A Repair
« Reply #41 on: September 25, 2018, 08:20:43 pm »
What is response on ID? command? I also always had various issues with Agilent pod, so I stopped using it since long ago. Using NI and Agilent E5810As instead.
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Re: Agilent 3458A Repair
« Reply #42 on: September 25, 2018, 08:37:24 pm »
What is response on ID? command? I also always had various issues with Agilent pod, so I stopped using it since long ago. Using NI and Agilent E5810As instead.

No responce from any command.....as if it was unplugged!......no LSTN on the display at any time.

The usb interfaces are very intermitted for sure, I am mainly using an 82350B PCI card which is miles better (but not perfect).

I just wondered if there was something else I needed to enable or something before I start looking/scoping a hardware fault (160/161 etc?).

Ian.
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Re: Agilent 3458A Repair
« Reply #43 on: September 28, 2018, 02:14:21 pm »
Hi all,

GPIB working now......I replaced both 75ALS160 & 161 transceivers and it's fine now.

I had scoped the I/O and it was dead, but I was seeing some wierd voltage levels on some of the signals. The controller I thought was probably ok because the enable and direction signals from the 9914 looked ok. Digikey had stock.

Pic below after changing out the IC's and clean up.

Ian.
« Last Edit: September 28, 2018, 02:19:03 pm by IanJ »
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Re: Agilent 3458A Repair
« Reply #44 on: September 28, 2018, 02:24:34 pm »
Great, thanks for follow up. I hope my third 3458 does not have dreaded new SMT version of A5.
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Re: Agilent 3458A Repair
« Reply #45 on: September 28, 2018, 03:52:31 pm »
Have seen many 3458a's with broken 160/161's. One of its standard deseases...
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Re: Agilent 3458A Repair
« Reply #46 on: September 29, 2018, 04:08:42 am »
probably the transceivers in my 3457 are not good, after GPIB interface clear the program will lost the instrument after an un-predictable time period.
the only way to get connected again is to issue GPIB interface clear once more, didn't have time to look into deep.  :scared:
 

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Re: Agilent 3458A Repair
« Reply #47 on: October 12, 2018, 03:34:49 pm »
Hi all,

Decided to take some readings from my 3458A's and see where they were, primarily interested in No.2. I have been playing around with some hardware & software to stabilize the workshop temperature 24/7 and can now play with the 3458A's knowing the ambient is stable. At the moment i've recorded 0.5degC change in past 36hrs and will tweak the setpoints to get it better.

No.1 (Feb 2000) = my original unit
No.2 (Jul 2009) = Repaired unit, new A3 board.

No.2 seems to be running a bit warm (factory flat type filter with spacer plate etc installed) compared to No.1 (original cup type filter), so I ran some tests with various materials to see how they compare including removing the metal spacer as it looks like it could restrict airflow.

The best I came up with (apart from no filter!) is a piece of stainless steel filter mesh cut to size and fitted without the plate but with the guard. This brought the temp down to just 1 degC above No.1.

Here's my tests of No.1 & No.2 before abandoning No.2 test to fix the filter issue.

No.1:
CAL? 72
36.4 to 36.7 degC
1-day Drift PPM = 0.0132
.....7-day test on-going.

No.2:
CAL? 72
40.4 to 41.2 degC
1-day Drift PPM = -0.3564
.....abandoned test

PS. Thanks to TiN for the spreadsheet idea (xdevs site), I've now made my own......

Filter removed and choosing mesh size:


App running controlling air-con unit and heater. Based on USB-TnH SHT10 temp probe.


Ian.


« Last Edit: October 12, 2018, 03:36:47 pm by IanJ »
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Re: Agilent 3458A Repair
« Reply #48 on: October 12, 2018, 04:00:41 pm »
A good excuse to buy a thermal camera!
 

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Re: Agilent 3458A Repair
« Reply #49 on: October 12, 2018, 04:11:59 pm »
An obvious point to check would be the power consumption. Different board versions can have different power requirement. Normally the newer parts tend to be lower power - but with all the replacement boards the new A3 might take more.
 

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Re: Agilent 3458A Repair
« Reply #50 on: October 12, 2018, 04:25:52 pm »
Both units back in-situ and powered up for about an hour......much better!
No.1 = 36.1degC
No.2 = 37.5degC

No.2 is stacked above No.1, with a 2" air space between them. There's a 2" air space below No.1 also.

Never thought to break out the C2 when it was in bits.......



Again, thanks to TiN for all the good 3458A stuff on the xdevs site.

Ian.
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Re: Agilent 3458A Repair
« Reply #51 on: October 14, 2018, 06:52:12 pm »
Hi all,

I've never really done any stability tests of my own on my original 3458A (purchased from AP) but thought after fitting the new A3 board to my repaired unit I'd run some tests......and also now that I have the workshop temperature stability properly sorted.
I've also got a PDVS2 hooked up throughout (DC powered) for an additional 10V test just for fun.

It's interesting to see the new A3 board just fitted compared to the one in my original unit.

Learning more about these units every day!

Results so far after 3 days:

Ian.






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Re: Agilent 3458A Repair
« Reply #52 on: October 17, 2018, 08:10:57 pm »
Update:-

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Re: Agilent 3458A Repair
« Reply #53 on: October 18, 2018, 01:02:05 am »
Looking healthy.  :-+
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