Electronics > Repair
Repair : HP 3245A precision DC/AC source
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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  ;D.
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