Repair : HP 3245A precision DC/AC source

[TiN]

Well, making precision +/-100V 4-quadrant amplifier is a task, half a step before actual SMU . Sorta what I have in mind doing for PA stage of my neverending project. That's also one of reasons why I got 3245A in first place, as reference to some extent.

Fan control...I'm not ready to open that pandora box yet. As this is looking onto weeks and weeks of careful testing and retesting to make sure those ppm-level values are correct. But I'd love to be corrected.
Obvious weak points of 3458A from fan would be tempco of current sense and current source range resistors and networks, perhaps front end input amplifier. Also we don't know if there is any firmware-implemented tempco correction in this aspect, assuming constant fan airflow, as in ADC...

[alanambrose]

>>> OK will add a count of readings to ignore at the beginning and also a count of readings to average.

B...x this dumb forum software lost my post....here's the abbreviated version. DCV only, AZERO on, 1s dwell between changing source and making first reading.

# ignored        # averaged       nplc          cal headroom %

       0                       1                100                  85
       1                       1                100                  85
       1                       5                100                  74
       1                     10                100                  74
       1                     10                  10                  89
       1                     30                  10                  85
       1                   100                  10                  83         
       1                       1              1000                  71           

(actually I'll post this and add the other results as they arrive)

Headroom of 90% means device is 10x better than spec, 100% means perfect device, 0% means on spec (on average over tests). This is with the averaging being done in software rather than in the device.

So, with this data at least, the benefit is marginal except for 10 samples of 10 nplc (rather than 1 of 100 nplc as in the cal manual). Looking at the detail, the barrier to a much tighter spec seems to be the low voltage offset - sometimes 10uV which throws off the low voltage sourcing. As the cal algorithm is a black box (e.g. it doesn't seem easy for the user to just adjust the low voltage offset) I'm not sure where to go from here.

I guess you could wrap an optimisation algorithm around it and let it run for days but....

My simple test set-up (below) - no low emf stuff. Will release this version as soon as I have tested it. This is suggesting to me TiN that your LTZ mod is having a good effect - I see the LM399 has ~15x noise of LTZ1000 so maybe that's it.

>>> we don't know if there is any firmware-implemented tempco correction

Well it doesn't seem to work too well if there is

[TiN]

Hm, interesting.

Probably does not matter, but I have 3245 and 3458 in different racks, not on top of each other. Also I did not use any fancy cables either, regular 45cm BNC -> BNC-BNC male-male -> 45cm self-made BNC to Copper gold-plated spadelug coax cable.

[PartialDischarge]

So how many are we with the nice 3458 3245 combo? 3?
Good news is that mines have no hardware errors. They need a good sanitization, new nvrams, new line filters, maybe new caps and a fresh cal.
Started with the first.

Feet are missing, will look for 3D models for the printer....

[TiN]

Why bother with printer? There are plenty on evil bay.

CalMachine about to join party too, he just missing 3458  .

[TheSteve]

I have a 3458A for CalMachine

[rastro]

Feet are missing, will look for 3D models for the printer....

You can pick feet up 8 for $8.00.
http://www.ebay.com/itm/HP-Agilent-Keysight-5041-8801-Cobb-Grey-Replacement-Feet-Set-Of-Eight-/401400063912?epid=15002971843&hash=item5d754ee7a8:g:VFYAAOSwuLZY2tCA

[CalMachine]

I have a 3458A for CalMachine

Why bother with printer? There are plenty on evil bay.

CalMachine about to join party too, he just missing 3458  .

First, I need to get the 3245A in working order!  It's coming with some failures and errors.  I also need to work on one of the Datron 1082s I got... the display was acting wonky and going in and out.  I think it might have been due to static or something, as display would change and react to my hand being close to it.

[PartialDischarge]

CalMachine, if you need comparative measures in the boards of the 3245 for repair, let me know while mines are still open and uncalibrated. 15 days most 

[CalMachine]

CalMachine, if you need comparative measures in the boards of the 3245 for repair, let me know while mines are still open and uncalibrated. 15 days most 

Will do   Thank you much!  The 3245 won't be in my possession until Tuesday, though.

[PartialDischarge]

Just cleaned all dust inside, installed the nvrams in sockets and changed filters for new ones with surge protection, a bit longer than the originals but there's still room. These units are pretty nice except for the display that has gone down in luminosity albeit still perfectly visible.

[Zucca]

Boom!

One more in the club!

I just got a HP 3245A with High Voltage OPT for 866,49 EUR delivered. TEA TEA TEA. List price was 1200€ 

eBay auction: #192335067589

Oh well, so crazy!

Now I have to get a HP3458A....

[nikonoid]

Nice! Congrats! I also got 3245a with high voltage option. It got mechanical damage in shipping, so it was only $140. I will put repair photos here, when I get to do the repair.

Any recommendations for replacement EMI filter brand/type for 3245a and 3458a? Does it make any difference? Thanks.


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[Zucca]

Very well!

Well I hope the transport damage didn't compromise the circuity inside.

What $140? It was a XMAS present to you?

And of course everybody will now post they got a 3245A for almost nothing... 

Let´s keep in touch! Well I need to finish some more project before to restore this puppy.

[nikonoid]

I guess I just got "lucky" with damage. I reseated a cable and got it to work. It is a bit out of spec but otherwise. If I was to get all damaged mechanical parts from keysight it will be about $400-$500, making it a bit less of a good deal.

I am fairly handy and have right tools. I am planning to do some sheet metal work and attempt to glue plastic before paying money to Keysight.

I am also planning to change emi filter, fan, and electrolytics.

In a same boat with you, I also need to finish few things before starting this one. Let's definitely start at in touch.



Sent from my iPhone using Tapatalk

[PartialDischarge]

Any recommendations for replacement EMI filter brand/type for 3245a and 3458a? Does it make any difference? Thanks.

Anyone you like, I hope schaffner has learned from the past by now, I used this one from mouser FN9222UZ-3-06 with surge protection, cause I live in a thunderstorm-prone area.

[View[+]Finder]

Based on the excellent writeup and video by TiN xdevs, I found a used HP3245A on eBay (where else?) for about the same $$ as was mentioned in the post. It arrived in better physical condition than expected, but was way out of calibration. Having to calibrate the old way with a DMM and manual input of voltage makes one appreciate the value-added in the 3458A calibration method. After my usual internal inspection and dust removal (no IPA this time) the 3245 was ready for warm-up and calibration.

The end result is that my 3245A has passed all the 'tests' and is in line with all the performance measures. One troublsome spot--perhaps due to the state of earlier cals (there had been 14)--there was a glitch related to Step 45. My first time the 'voltage' indicated -.004 so that's what I entered, but after that Step 46 and 47 were out of line with the example in the book and the calibration was not accepted. (What a PITA: I can go for coffee while the 3458 chugs along on the volts cal)

Without wasting too much time on precision, I started another cal and used the 'book value' for Step 45. It worked, but not as well as possible. My next cal was done with care on volts only and I recorded the entries on paper. I used .0001 for the Step 45 in lieu of the slightly negative 'suggestion' from the 3245, just wanting to see if that would give better results. It did; much better.

The final was a full cal and all voltages were fed to the 3458 (NPLC 200) and to my 34465 DMM set up to collect a histogram of readings at 1 PLC. Both meters were reading the same voltage from the 3245 and the 34465 was set on 'High Z' so as not to load things down. Each run of the histograms captured over 1000 obs and sometime several times that. By observation, each histogram was checked for skewness, kurtosis and bi-modality and restarted if needed. With a stable and reliable histogram, the consistency of mean and standard deviation were used to indicate the end of the run. The mean value of voltage was used as the input to the 'CAL VALUE' on the 3245. This was usually close to the value displayed on the 3458, but when different, the 34465 'mean' was used. Current calibration was done with the 34465 alone using the same process as above.

The 'histogram' method improved a bit on the 'straight from 3458' as suggested in the 3245 cal manual. Performance results that were near the edge of the range were now close to the center in all cases.

[View[+]Finder]

Has anyone done any investigation /experimentation around the 3245's frequency generator? There doesn't seem to be any way to calibrate, so I assume there is a crystal oscillator running the show. For example at 300kHz dialed in on the 3245 and measured on a HP5316B counter (with 10kHz Rh reference) it shows 300.0035E3. The 3458A shows the same. On the o'scope there seems to be an occasional glitch maybe from a higher frequency.

Not a big deal, but if anyone has more info . . ..

Probably well within the specs for an instrument of that age.

Thanks

[Samogon]

Are you accepting new members?

I have got 3245A with startup error "92 Bus Source issue"
Measured all voltages on A6 (PSU) all voltages are good except 15V at J15 shows 21V. Measured P2 connector pins 1 and 2 give 17VAC as i understand transformer output too high. In order to have 15VDC after bridge rectifier and filter capacitor we need to have 10VAC input.
Line set to 120VAC. And what i suppose to think? Transformer? This unregulated 21V goes to backplane A2 and there distributed to source A1. I thinking to place voltage regulator between A6 (PSU J15) and A2(Back plane).
What do you think?
BTW i have supplied 15V to A2 from lab supply and it did not fix an error. So i assume A1 is damaged.

[TiN]

Isolated voltages on A1 generated by separate switching supply, so higher input voltage does not matter much I think.

Check BP error signal generation circuitry on backplane.
IMG

[Samogon]

Ok removed both source cards and here we are BBQ
Installed only CH1 card and we are alive, no errors, selftest passed.
So at least i have one good card and one toasted, this is much easier to repair since they are identical, so i even can do offline component comparison.
Not bad outcome.

[TiN]

Sweet, now pimp it with LTZ!

[nikonoid]

Samogon, congrats on having one channel working. Second should be fairly easy.

I have the 3245a version with 10x output (100V).

Even without LTZ mine is fairly good at 10V (give or take few ppm). Now 10x output is off by quite a bit +28ppm.  I cannot find a way to adjust that. The zero for 10x output is adjustable with a cal pot on a side.

Would anyone know if there a good way to adjust magnitude of 10x output?

[Samogon]

I have Fluke 732A on the way, so i dont see reasons except curiosity  for LTZ. I rather would like to get x10 card. If i get  x10 i would get rid of Tek TM506 with TG506 sinse i need 50V square wave 1kHz

[Samogon]

So far i have found K3 relay is stuck in open not latched, and mosfet Q901 short as i expected due to our burnt friend C900.
Something catastrophic happened.